THE HANDBOOK ON

SOLIDS CONTROL &WASTE MANAGEMENT

4th EDITIONPublished by Brandt / EPI

1st Edition 19822nd Edition 19853rd Edition 19954th Edition 1996

All rights reserved. No part of this book may be reproduced inany form without permission in writing from the publisher.

Printed in the U.S.A.

iPREFACE

This Handbook was written by the Technical Services staff of Brandt/EPIto provide a basic understanding of effective mechanical removal of drilledsolids and management of drilling wastes. Based on sound theoretical con-cepts, this Handbook is a practical working tool. It is designed for use byanyone needing to optimize drilling efficiency: drilling engineers, supervi-sors, tool pushers, mud engineers, derrick hands, service personnel andothers.

This 4th edition of the Handbook provides updated sections on equip-ment and techniques, and includes new information on waste processingsystems, including downhole injection, solidification/ stabilization, waterclarification, and other site remediation techniques. We would appreciateany suggestions for improving future editions of the Handbook. Pleaseaddress your comments to:

Brandt/EPI Technical GroupP.O. Box 2327Conroe, TX 77305

TEL: (713) 756-4800FAX: (713) 756-8102

Thanks,

Mike MontgomeryManager, Technical GroupBrandt/EPI

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TABLE OF CONTENTS

PAGE1.0 DRILLING MUD AND MUD SOLIDS .....................................................1.1

1.1 Functions of Drilling Mud ............................................................................1.11.2 The Nature of Drilled Solids ........................................................................1.21.3 Properties of Drilling Mud ...........................................................................1.41.4 Types of Drilling Muds.................................................................................1.8

2.0 BENEFITS OF SOLIDS REMOVAL BY MECHANICAL SEPARATION.....2.12.1 Reduced Total Solids ....................................................................................2.12.2 Reduced Dilution Requirements ..................................................................2.2

3.0 MECHANICAL SOLIDS CONTROL AND RELATED EQUIPMENT .........3.13.1 Particle Classification and Cut Point ............................................................3.33.2 Separation by Vibratory Screening ..............................................................3.63.3 Shale Shakers ..............................................................................................3.143.4 Mud Cleaners/Conditioners........................................................................3.213.5 Separation by Settling and Centrifugal Force............................................3.283.6 Sand Trap ....................................................................................................3.293.7 Hydrocyclones ............................................................................................3.303.8 Desanders....................................................................................................3.333.9 Desilters.......................................................................................................3.353.10 Decanting Centrifuge..................................................................................3.383.11 Auxiliary Equipment...................................................................................3.433.12 Unitized Systems.........................................................................................3.483.13 Rig Enhanced Systems................................................................................3.493.14 High Efficiency Solids Removal Systems...................................................3.503.15 Basic Arrangement Guidelines...................................................................3.51

4.0 BRANDT/EPI PRODUCTS AND SERVICES ........................................4.1Company Profile..........................................................................................................4.14.1 Scope of Services..........................................................................................4.14.2 Business Relationship...................................................................................4.14.3 Certification...................................................................................................4.14.4 Personnel Resources.....................................................................................4.2Products and Services .................................................................................................4.24.5 Linear Motion Shakers..................................................................................4.3

ATL-1000 .......................................................................................................4.3ATL-1200 .......................................................................................................4.3LCM-2D .........................................................................................................4.4ATL-CS...........................................................................................................4.4LCM-2D/CM2 ................................................................................................4.5ATL Drying Shaker........................................................................................4.5SDW-25 Drying Shaker.................................................................................4.6ATL-16/2 Mud Conditioner...........................................................................4.6ATL-2800 Mud Conditioner ..........................................................................4.7LCM-2D Mud Conditioner ............................................................................4.7

4.6 Orbital Motion Screen Separators ................................................................4.7Tandem Screen Separator ............................................................................4.7Standard Screen Separator ...........................................................................4.8Mud Cleaners ................................................................................................4.8

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4.7 Screen Panels ................................................................................................4.9BlueHexSM 3HX Screen Panels .....................................................................4.9Pinnacle Screen Panels .............................................................................4.9PT Screen Panels ........................................................................................4.10Hook-Strip Screen Panels...........................................................................4.10

4.8 Hydrocyclone Units ....................................................................................4.10Desanders....................................................................................................4.10Desilters.......................................................................................................4.11

4.9 Centrifuges ..................................................................................................4.11SC-1 Decanting Centrifuge .........................................................................4.11SC-4 Decanting Centrifuge .........................................................................4.12HS 3400 High Speed Decanting Centrifuge ..............................................4.12SC 35HS High Speed Decanting Centrifuge..............................................4.12HS 5200 High Speed Decanting Centrifuge ..............................................4.13Roto-Sep Perforated Rotor Centrifuge .......................................................4.13

4.10 Dewatering Units ........................................................................................4.144.11 Filtration Units ............................................................................................4.144.12 Vacuum Degassers......................................................................................4.154.13 Mud Agitators..............................................................................................4.154.14 Portable Rig Blowers ..................................................................................4.154.15 Integrated Systems......................................................................................4.16

Closed Loop Processing Systems ...............................................................4.16Coiled Tubing (CT) Processing Systems....................................................4.17Trenchless Technology Processing Systems..............................................4.17Live Oil Systems..........................................................................................4.17

4.16 Remediation Management Services ...........................................................4.174.17 Technical & Engineering Services..............................................................4.18

APPENDICESGlossary .....................................................................................................................A.2Mud Solids CalculationsStandard Calculations..................................................................................................B.1Field Calculations to Determine Total Solids Discharge...........................................B.4Field Calculations to Determine High and Low Gravity Solids Discharge ..............B.5Solids Control Performance Evaluation .....................................................................B.6Method for Comparison of Cyclone Efficiency .......................................................B.10Mud Engineering DataConversion Constants and Formulas..........................................................................C.1Density of Common Materials ....................................................................................C.2Hole Capacities ...........................................................................................................C.3Pounds per Hour Drilled Solids Fast Rates ..........................................................C.4Pounds per Hour Drilled Solids Slow Rates .........................................................C.5Solids Content Chart ...................................................................................................C.6Equipment SelectionPre-well Project Checklist...........................................................................................D.1Screen Cloth Comparisons .........................................................................................D.2Brandt/EPI Equipment Specifications........................................................................D.3Selecting Size and Number of Agitators ....................................................................D.7Brandt/EPI Sales & Service Locations ....................................................................D.8

1.1

1.0 DRILLING MUD AND MUD SOLIDS

Mud is the common name fordrilling fluid. While it is outside thescope of this handbook to offer adetailed discussion of drilling fluids,a brief outline of the general char-acteristics of drilling mud isincluded to establish the basic rela-tionships between drilling mud andsolids control.

Similarly, any discussion of solidscontrol would be incomplete with-out establishing an understandingof the nature of mud solids theirsize, shape and composition.

1.1 FUNCTIONS OF DRILLING FLUID

The mud system in a drillingoperation performs many importantfunctions. Among these are: 1. Carry the drilled solids from

the bottom of the hole to thesurface.

2. Support the wall of the hole. 3. Control pressure within the for-

mation being drilled.4. Cool the bit and lubricate the

drill string.5. Clean beneath the bit.6. Suspend cuttings while circula-

tion is interrupted (e.g., duringtrips).

7. Secure accurate informationfrom the well (cuttings sam-ples, electric logs, etc.).

8. Help support the weight of thedrill string.

9. Transmit hydraulic horse-power to the bit.

10. Allow removal of cuttings bythe surface system.

Of the ten functions listed, the fol-lowing are generally consideredmost important:1. Drilling mud moves the forma-

tions solids cut by the drill bitfrom the bottom of the hole tothe surface. Removal of cut-tings from the wellbore isessential in order to continuedrilling.

2. Drilling mud must withstandthe pressure exerted by theformations exposed in thehole. The pressure exerted bythe mud against the formationshelps the driller control thepressure created by the gas, oiland water that are exposedwhile drilling, thus reducingthe potential for costlyblowouts.

3. Drilling mud protects and sup-ports the walls of the wellbore.The mud has a plastering effecton the walls of the hole andhelps prevent the walls fromcaving in, causing an enlargedhole or leading to stuck pipe.

1.2

These problems significantlyincrease drilling expense andtime.

4. Drilling mud cools the bit andlubricates the drill string. Thisfunction is important in drillingbecause it increases the usefullife of bits and the drill string.

Drilling mud is obviously a majorfactor in the success of any drillingprogram, and the key to any effec-tive mud system is good solidscontrol.

1.2 THE NATURE OF DRILLED SOLIDS

Mud solids include particles thatare drilled from the formation,material from the inside surface ofthe hole and materials that areadded to control the chemical andphysical properties of the mud,such as weight material. Drilledsolids particles are created by thecrushing and chipping action ofrotary drill bits. Additional solidsenter the well bore by sloughingfrom the sides of the open hole.

The unit of measurement general-ly used to describe particle size isthe micron (). A micron is onethousandth (0.001) of a millimeter,or approximately 0.00003973 of aninch. To relate this unit of measure-ment in more familiar terms, Figure1-1 provides a list of common itemsand their size in microns.

Although individual mud solidscan range in size from less thanone micron to larger than a humanfist, the average particle size is lessthan 3540 microns, too small to beseen with the human eye.

Note: The various sizes of solidsparticles in a particular drillingmud are referred to as the mudscuttings, sand, silt or clay content.This content is important to remem-ber because solids control practiceswill affect the average particle sizeand the concentration of solids inspecific size ranges which maygreatly affect mud properties anddrilling operations.

Mud solids may be convenientlygrouped according to micron sizerange, but unfortunately not with-out introducing some element ofconfusion. The API Committee onStandardization of Drilling FluidMaterials, in API Bulletin 13C pub-lished in 1974, recommendedcertain terminology for mud solidsparticle size in an attempt to mini-mize this confusion. This newterminology has not yet, however,gained universal acceptance.

Figure 1-1 Micron Size Range of Common Materials

ITEM DIAMETER IN MICRONS

Cement Dust (Portland) 3-100 Talcum Powder 5-50 Red Blood Corpuscles 7.5 Finger Tip Sensitivity 20 Human Sight 35-40 Human Hair 30-200 Cigarette (diameter) 7520 One inch 25,400

1.3

The more commonly used classifi-cations shown in Figure 1-2,cuttings, sand, silt and clay (or col-loidal size) will be used throughoutthis handbook, as they are the mostreadily recognized in the field.These terms will refer to size classi-fication only, not to materialcomposition.

Note: Drilled solids can originatefrom sand, limestone, shale or otherformations, but their classificationin regard to solids control usuallydepends on particle size since theirspecific gravity is assumed to beapproximately 2.6.

It is important to note that com-mercial solids (such as barite orbentonite added for weight and vis-cosity) are also affected by solidscontrol equipment, according tosize. Most barite particles are in thesame size group as silt (274microns); bentonite particles aregrouped with clay (smaller than 2microns).

From the time they enter the welluntil they reach the surface, drilledsolids particles are continuouslyreduced in size by abrasion withother particles and by the grindingaction of the drill pipe.

Abrasiveness of mud solids isdetermined by particle shape andhardness. Drilled solids come invarious shapes such as round, nee-dle shaped, platelets, cubic, etc. Tobe destructive, particles must besharper and harder than the materi-al they are to abrade. Figure 1-3illustrates the degradation of drilledsolids in a mud system. The mainbody of the particle becomes lessabrasive with wear as the mostabrasive corners continue todegrade down through the silt sizeto approximately 1520 microns.

Particles smaller than 1520microns have much less abrasiveeffect on drilling equipment. Bariteparticles, which are not as hard asmost drilled solids, are generallyless abrasive than similarly-sizeddrilled solids. Other weightingmaterials, such as hematite, aregenerally harder and more abrasivethan barite.

Specific surface area, as it relates

Figure 1-2 Common Field Terminology of Particle Size

CLASSIFICATION PARTICLE SIZE(Diameter in Microns)

Cuttings Larger than 500

Sand 74-500

Silt 2-74

Clay Smaller than 2

Figure 1-3 Mechanical Degradation of Drilled Solids

1.4

to various shapes and sizes ofsolids, is another important con-cept. Specific surface area refers tothe surface area per unit of weightor volume. Figure 1-4 lists examplesthat show surface area greatlyincreases per unit of mass: 1) asparticle size decreases, and 2) asparticles become less spherical inshape.

Surface area adsorbs or ties-upwater. The more surface area, themore water adsorbed. As the parti-cle size decreases toward thecolloidal size, the relative effect ofthe water coating increases. Thespecific surface area has a pro-nounced effect on viscosity, asFigure 1-5 illustrates. The higher therelative specific surface area, thegreater is the viscosity. Formations

composed of clays that easily dis-perses into the mud producerelatively more viscosity increase andwill have wetter separations inremoval by equipment than forma-tions that produce larger sized solids.Bentonite disperses easily into col-loidal solids and also absorbs muchmore water than most solids types.Hence bentonite builds viscosity atrelatively low concentrations.Viscosity and other mud propertiesare discussed in Section 1.3 of thisHandbook.

1.3 PROPERTIES OF DRILLING MUD

The ability of a drilling fluid toperform its functions depends onvarious properties of the mud, mostof which are measurable and areaffected by solids control.

DENSITY (MUD WEIGHT)

Density is a measure of the weightof the mud in a given volume, andis frequently referred to as mudweight. The instrument used tomeasure density is the mud balance(see Figure 1-6). The instrumentconsists of a constant volume cupwith a lever arm and rider calibrat-ed to read directly the density ofthe fluid in lbs/gal (water = 8.33lbs/gal) and pressure gradient inpsi/1000 ft (water = 433 psi/1000 ft)or pounds per cubic foot (water =62.4 lbs/ft).

Figure 1-4Effect of Particle Size and Shape on Surface Area

Figure 1-5Effect of Specific Surface Area on Viscosity

EQUIVALENT SPHERICALPARTICLE DIAMETER TYPE SQUARE FEET

(Microns) PARTICLES PER POUND

5.0 Glass Spheres 2,345

5.0 Crushed Quartz 3,435

1.0 Glass Spheres 11,725

1.0 Crushed Quartz 17, 160

0.1 Glass Spheres 117,250

0.1 Crushed Quartz 171,500

1.5

The density of the mud is relatedto the specific gravity of the fluid.Specific gravity is the ratio of amaterials density to the density ofwater. Pure water has a specificgravity of 1.0. A material twice asdense as water would have a spe-cific gravity of 2.0. A material halfas dense as water would have aspecific gravity of 0.5. Low gravitysolids have an average specificgravity of 2.6. The solids are 2.6times the weight of the same vol-ume of water.

VISCOSITY

Viscosity measures the mudsresistance to flow as a liquid and isone of the key physical propertiesof mud. Increasing the amount ofsolids or exposed surface area in amud increases its resistance to flowas a liquid and therefore increases

its viscosity. Viscosity is routinelymeasured with a Marsh Funnel andMud Cup at the drilling site (seeFigure 1-7). The person measuringthe viscosity fills the funnel with asample of mud and allows it to

Figure 1-6 Mud Balance

Figure 1-7 Marsh Funnel and Cup

1.6

flow through the tip of the funnelcontainer while measuring the timein seconds that it takes to fill themud cup to the one quart level.The funnel viscosity recorded is inseconds per quart. Internationally,funnel viscosity is recorded in sec-onds per thousand ccs or secondsper liter.

PLASTIC VISCOSITY

A muds Plastic Viscosity is the por-tion of a muds flow resistancecaused by the mechanical frictionbetween the suspended particlesand by the viscosity of the continu-ous liquid phase. In practical terms,plastic viscosity depends on thesize, shape, and number of parti-cles. For example, as the amount ofdrilled solids in a mud increases,the plastic viscosity also increases.

Plastic viscosity is measured with a

rotational viscometer (Figure 1-8)and is expressed in centipoise(grams per centimeter-second).

YIELD POINT

Yield point is the part of flow resis-tance that measures the positiveand negative inter-particle, orattractive, forces within a mud.Yield point is measured with aviscometer and expressed inlbs/100 ft2. Internationally, yieldpoint is sometimes measured indynes/cm2.

GEL STRENGTH

Gel Strength is a function of amuds inter particle forces and givesan indication of the amount of gela-tion that will occur after circulationceases and the mud remains staticfor a period of time. Typically, gelstrengths are reported for initial and10-second gel strength. A largedeviation of these two figures mayindicate progressive gels, that is,gelation structures that gainstrength over time. Gel strength isalso measured with a viscometerand expressed in lbs/100 ft2.Internationally, gel strength issometimes measured in dynes/cm2.

SOLIDS CONTENT

The solids content is the volumepercentage of the total solids in the

Figure 1-8 Rotational Viscometer (VG Meter)

1.7

mud. To determine the solids con-tent of a mud containing weightmaterial, a mud container in theretort is filled with a measured vol-ume of mud (see Figure 1-9). Themud is then heated to boil off theliquid. The percentage of the liquiddistilled off is measured in a glasscylinder and subtracted from 100%.The difference is the percentage ofsolids by volume contained in thedrilling mud and is recorded as per-centage solids. The total solids fromthe retort and mud weight are usedto calculate the low and high gravi-ty solids content.

If the mud does not contain oil orweight material, such as barite orhematite, the low gravity solids canbe determined without a retort byweighing the mud and referring toa solids content chart.

SAND

Sand is any particle larger than 74

microns when referring to solidscontrol separation. Therefore, thesand content of a mud is simply theamount of solids too large to passthrough a US Test Sieve 200-meshscreen. This is determined with asand content set (see Figure 1-10)by washing a mea-sured amount ofmud through the200-mesh screen inthe kit. Theamount of solidsthat does not passthrough the screenis measured aspercentage by vol-ume and isrecorded as per-cent sand.

FILTRATION

Filtration and wall-cake buildingare actions that the drilling mudcarries out through and on thewalls of the hole. Some formationsallow the liquid in the mud to seepinto them, leaving a layer of mudsolids on the wall of the hole. Thislayer of mud solids is called filtercake or wall-cake. The filter cakebuilds up a barrier and reduces theamount of the liquid that enters theformation and is lost from the mud.This process is referred to as filtra-tion, or fluid loss. The instrumentused to measure the fluid loss dueto filtration is a filter press (seeFigure 1-11).

Figure 1-9 Retort (Mud Still)

Figure 1-10Sand Content Set

1.8

The person using the filter pressplaces a mud sample in the instru-ment on top of a piece of filterpaper and brings the pressure up to100 pounds per square inch. Theamount of fluid flowing from thesample in 30 minutes is measuredin milliliters. The mud filtrationproperty is recorded in units ofcubic centimeters (ccs) or milliliters(ml) per 30 minutes. Examination ofthe filter paper will indicate howthe solids will plaster the wall ofthe hole and affect fluid loss. Thecake thickness is recorded in unitsof 1/32s of an inch.

CHEMICAL PROPERTIES

Chemical Properties is a broadcategory, including measurementsof pH, alkalinity, chlorides, calcium

content, salt content, and otherproperties that affect drilling mudperformance. Some of these chemi-cal properties can be controlledthrough various mud additives thatthicken, thin, precipitate, disperse,emulsify, lubricate or otherwiseadjust the mud depending on spe-cific drilling needs. For example,caustic soda can be added to somesaltwater mud in order to maintaina high pH level; it makes disper-sants more effective and reducescorrosion. Chemical changes suchas these are used to fine tunedrilling muds.

1.4 TYPES OF DRILLING MUDS

Drilling fluids are generally cate-gorized as water-base or oil-base, and as weighted orunweighted muds.

Water-base Muds contain water asthe liquid phase and are used todrill most of the wells in the worldbecause they are relatively simple,expense is usually reasonable, andwater is commonly available inmost places.

Oil-base Mud contains either nat-ural oil or synthetic oil as thecontinuous liquid phase and is usedfor maximum hole protection. Oil-base mud and synthetic oil mud areusually much more expensive thanwater-base mud and therefore areonly used when there is a specific

Figure 1-11 Filter Press

1.9

need, such as to keep the holefrom swelling or caving in, or toreduce friction and prevent stuckpipe in very crooked or high angleholes. Either water-base or oil-basemud can be used as weightedmud.

Weighted Mud refers to any mudwhich has barite or barite substi-tutes added to increase density.These muds normally have a densi-ty greater than 10.0 lbs/gal. Thesolids in weighted mud consist ofdrilled solids from the hole, plusbarite, plus commercial clays addedto control fluid loss and viscosity.

Unweighted Mud refers to anymud which has not had bariteadded. This mud type normally hasa density of less than 10.0 lbs/gal.The solids in unweighted mud con-sist of drilled solids from the hole,plus commercial clays.

Solids control techniques will varyconsiderably depending on the typeof mud being used. For example,with many unweighted water-basemuds, the loss of fluids along withthe drilled solids may be economi-cally insignificant, allowing simplesolids control techniques. In thecase of mud that contains expen-sive chemical additives and/orbarite, especially oil-base mud,sophisticated solids control tech-niques must be utilized to minimizeoverall costs. In addition, environ-mental costs of haul-off and

disposal may require sophisticatedsolids control techniques. Systemrecommendations for specific appli-cations are covered in detail inChapter 4.

Here is a list of the most commonmud types, followed by a briefdescription of each type:I. Water-Base Mud (WBM)

A. Spud MudB. Natural mudC. Chemically-Treated Mud

1. Lightly Treated ChemicalMud

2. Highly Treated ChemicalMud

3. Low Solids Mud4. Polymer Mud5. Calcium Treated Mud

D. Saltwater Mud1. Sea Water Mud2. Saturated Salt Mud

II. Oil-Base Mud (OBM)A. True Oil BaseB. Invert Emulsion C. Synthetic (SBM)

SPUD MUD

Spud Mud is used to start thedrilling of a well and continues tobe used while drilling the first fewhundred feet of hole. Spud mud isusually an unweighted water-basemud, made up of water and naturalsolids from the formation beingdrilled. It may contain some com-mercial clay, added to increaseviscosity and improve wall-cakebuilding properties.

1.10

NATURAL MUD

Natural Mud (sometimes callednative mud) is usually unweight-ed water-base mud which containsmostly drilled solids. Some ben-tonite and small amounts ofchemicals may be used to improvefilter cake quality and help preventhole problems. This mud is oftenthe next mud type used after spudmud. Often, natural mud is used todrill the first few thousand feet ofhole, where only minor hole prob-lems are expected.

CHEMICALLY TREATED MUD

Chemically Treated Mud is water-base mud which contains chemicalsto control physical and chemicalproperties. Bentonite is usuallyadded to help control viscosity andfluid loss. Barite (weight material)may be added to increase density.

This mud is used where moresevere hole problems are expected,in order to prevent these problems.

Lightly Treated Chemical Mud isusually unweighted water-basemud. It is used where minor holeproblems are expected, such assloughing or caving of the walls ofthe hole.

Highly Treated Chemical Mud isusually weighted, water-base mudthat contains larger amounts ofchemicals, bentonite, additives, andbarite to maintain strict control ofviscosity, fluid loss, chemical prop-

erties, and density. Chemical mudsare often treated with lignosul-fonates or lignite and are thereforecommonly called lignosulfonatemud or lignite mud.

These muds are used where mod-erate to severe hole problems areexpected or high down-hole pres-sures occur. Of all the water-basemud types, these are the mostexpensive to maintain. As mud den-sity is increased and potential holeproblems (such as stuck drill pipe)become more of a risk, the removalof drilled solids by mechanicalsolids control equipment becomesincreasingly important.

Low Solids Muds are water-basemud containing less than ten per-cent (10%) drilled solids; 15% is anormal range. Generally speaking,the lower the solids content in themud, the faster the bit will drill.

Low solids muds are usuallyexpensive to maintain because thesolids, chemical, and fluid lossproperties have to be kept veryclose to prescribed levels. It isabsolutely essential that all solidsremoval equipment operate at max-imum effectiveness in order tomaintain the desired low level ofsolids at a reasonable cost.

Polymer Muds are special types oflow solids mud which contain syn-thetic materials, polymers, designedto control viscosity and fluid loss.Polymers are very expensive and

1.11

often difficult to screen when ahigh viscosity fluid is used.

Calcium Treated Muds are specialwater-base muds, usually weighted,which have lime or gypsum added.Calcium Treated Muds are normallyused to prevent shale type forma-tions from swelling or sloughing problems which could lead to stuckpipe or a ruined hole.

SALTWATER MUD

Saltwater Muds contain a highconcentration of salt. They may beweighted or unweighted.

Sea Water Muds contain sea wateras the continuous phase and, usual-ly, only sea water is used fordilution. They may be weighted orunweighted. These muds are usedoffshore and in bay areas wherefresh water is not readily available.

When sea water mud is beingused, only sea water should beused to rinse or wash the screens insolids control equipment.

Saturated Salt Muds (sometimescalled brine fluids) contain as muchsalt as can be dissolved in the waterphase. This mud type is often usedto drill through salt formations sothe fluid will not dissolve the saltformation. If fresh water mud isused, greatly enlarged holes wouldresult, usually leading to hole trou-ble.

It is important to be aware of theuse of salt mud because screen

blinding can occur when salt driesand cakes on the solids controlequipment. Fresh water may beused to clean the screens, but itmust be used very carefullybecause too much fresh water canupset the chemical balance of thismud.

TRUE OIL-BASE MUD

True Oil-base Mud contains aliquid phase with ninety to ninety-five percent (9095%) diesel oil andfive to ten percent (510%) wateremulsified within the oil. Thesemuds often use asphaltic type mate-rials suspended in the liquid forcontrolling viscosity and fluid loss.True oil-base muds provide goodhole protection, especially in shaletype formations, and also increasedrill string lubrication.

INVERT EMULSION MUD

Invert Emulsion Mud is oil-basemud in which the liquid phase issixty to ninety percent (6090%)diesel oil with ten to forty percent(1040%) water emulsified withinthe oil. An invert mud can be for-mulated with mineral oil or otherlow environmental risk oil substi-tutes when needed. In this mud,water and chemicals are used to-gether to control viscosity and fluidloss. Invert emulsion muds providegood hole protection and are themost commonly used oil mud.

1.12

SYNTHETIC OIL MUDS

The term Synthetic-Based Mud,or SBM, describes any oil-base mudthat has a synthesized liquid base.Some common synthetic base fluidsinclude linear alphaolefins (LAO),straight internal olefins (IO), polyal-phaolefins (PAO), vegetable oils,esters, and ethers. This base fluid isthen combined with viscosifiers,weighting material, and other addi-tives to produce a stable, usefuldrilling fluid.

SBMs share several advantageswith traditional oil-base muds,including excellent wellbore stabili-ty, improved drilling rates, goodhole cleaning, excellent cuttingsintegrity, and reduced torque.SBMs also provide additional healthand safety benefits higher flashpoints, lower vapor production, and

reduced eye and respiratory irrita-tion. The major benefit of SBMsover traditional OBMs is thereduced environmental impact ofcuttings and liquid mud. Currently,SBMs and cuttings meet U.S. off-shore environmental requirementsand may be discharged underWBM protocols.

SBMs are expensive, $200400/bbl., depending on the oil/waterratio. Proper solids removal and liq-uid recovery techniques must beused to maintain desired fluid prop-erties and drilling rate, and tocontrol mud maintenance costs.The alternatives to mechanicalsolids control dilution and wholeSBM additions are prohibitivelyexpensive when compared to thecost of proper solids control equip-ment.

2.1

INTRODUCTION

Of all the problems that couldconceivably occur during thedrilling of a well, mud contamina-tion from drilled solids is acertainty. The volume and type ofsolids present in drilling mud exerta considerable influence over mudtreating costs, drilling rates,hydraulics, and the possibility ofdifferential sticking, kicks, and lostreturns. Solids control is one of themost important phases of mud con-trol it is a constant issue, everyday, on every well. If drilled solidscan be removed mechanically, it isalmost always less expensive thantrying to combat them with chemi-cals and dilution.

The primary reason for usingmechanical solids control equip-ment is to remove unwanted drilledsolids particles from the mud inorder to prevent drilling problemsand reduce mud and waste costs,thereby reducing overall drillingcosts. The benefits of solidsremoval by mechanical separationcan best be seen in terms of twooutcomes: 1) reduced total mudsolids and 2) reduced dilutionrequirements.

2.1 REDUCED TOTAL SOLIDS

The presence of large amounts ofdrilled solids in a drilling mud usu-ally spells trouble for the drillingoperation. These solids adverselyaffect the performance characteris-tics of the mud and can lead to amultitude of costly hole problems.

Drilled solids decrease the life ofa mud pumps parts and thus, candecrease drilling efficiency due tolost time for pump repairs.Continued recirculation of drilledsolids produces serious mud prob-lems because recirculated solidswill gradually be reduced in size.The smaller the solids become, themore they negatively influence mudproperties and hydraulic perfor-mance. The greatest impact of thesolids is seen in reduced ROP. Thehigher the drilled solids content,the lower the penetration rate.

If mud solids are not properlycontrolled, the muds density canincrease above its desired weightand the mud can get so thick that itbecomes extremely difficult or evenimpossible to pump.

Since the earliest days of the oil-field, drillers have been trying tocombat high solids content throughthe use of settling pits. However,

2.0 BENEFITS OF SOLIDS REMOVAL BY MECHANICAL SEPARATION

2.2

some drilled solids are so finelyground that they tend to remain insuspension. This results inincreased mud viscosity and gelstrength which, in turn results inlarger particles also remaining insuspension. Thus, the approach ofremoving cuttings through settlingalone is of limited practical value.

Solids control equipment wasdeveloped in order to more effec-tively remove unwanted solids fromdrilling mud. A variety of devices(which will be discussed in detail inChapter 3 of this handbook) areavailable which mechanically sepa-rate the solids particles from theliquid phase of the mud. Thus thedriller, depending on the particularsituation and equipment used, canregulate to a fine degree theamount and size of solids particlesthat are removed or maintained inany given drilling mud.

Such control of mud solids throughmechanical separation allows themud to perform its drilling-relatedfunctions and avoids the downholeproblems caused by excessive solidscontamination. Effective solids con-trol permits viscosity and density to bekept within desired levels, dramati-cally increases the life of pump partsand drill bits, and promotes fasterpenetration all of which decreasethe time and expense of drilling.

2.2 REDUCED DILUTION REQUIREMENTS

A common method of trying tooffset the build-up of drilled solidsis the addition of more liquid. Thisis known as dilution and does notremove cuttings but reduces (ordilutes) their concentration in adrilling mud, thereby reducing thepercent of total solids in the mud.

However, it is important to notethat dilution is expensive. Everybarrel of dilution water (or oil)added requires an additionalamount of chemicals, barite orother materials in order to maintaindesired mud properties. The lowerthe drilled solids content to bemaintained, the greater the dilutionrequired. In the case of an oil-basemud, oil must be used for dilution which can become extremelyexpensive.

It should be noted that chemicaltreatment alone will ultimatelyresult in high solids content anduncontrollable mud properties. Themost effective approach is to usemechanical solids control equip-ment to remove as much of thedrilled solids as possible beforethey are incorporated into the mudsystem and then treat what is leftwith appropriate amounts of chemi-cals and dilution.

Effective solids removal bymechanical separation can maintaina minimum solids level in drilling

2.3

mud and greatly reduce the needfor dilution. Reducing the need todilute the mud can drasticallydecrease the cost of having to pur-chase mud products such as weightmaterial (barite) and chemicals.These materials are expensive mud costs can be 10% of the totalcost of drilling a well.

The Dilution Ratio Chart (Figure2-1) can be used indirectly toapproximate the amount of dilutionthat can be eliminated by use ofsolids removal equipment. Forexample, suppose a drilling engi-neer required that no more than 5%solids were to be maintained in anunweighted mud. The chart showsthat at 5%, each barrel of mudwould contain about 45 pounds ofdrilled solids. If solids controlequipment were removing 1 ton(2000 lbs) of solids per hour, thenthe equipment would save 2000

45 = 44 barrels of dilution per hour.If the chemicals and additives wereworth only $10 per barrel, the mudtreating costs would be reduced byapproximately $440 per hour! Overthe life of a drilling operation, $440per hour adds up to a very signifi-cant cost savings.

The same procedure can be usedto show reduced dilution require-ment in weighted mud. Whenheavily weighted muds (1618lbs/gal) are being used, drillingusually proceeds more slowly andless drilled solids are removed perhour. However, if approximately 5%drilled solids are allowed in themud, then each barrel of mud stillcontains roughly 44 pounds ofdrilled solids.

Therefore, if the solids controlequipment were removing even apencil-sized stream of solids whichwould amount to 44 pounds per

MUD WEIGHT(LBS/GAL)

TO BE MAINTAINED

8.58.68.78.88.99.09.19.29.39.49.59.69.79.89.9

10.0

DRILLED SOLIDS

PERCENT BYVOLUME

1.22.02.73.54.25.05.76.47.28.08.79.4

10.211.011.712.4

POUNDS OF2.6 SPECIFIC GRAVITY

SOLIDS PER BARREL OF MUD

11182532384552596673798693

100107114

BBLS OF WATERREQUIRED TO DILUTE

1 TON SOLIDS ANDMAINTAIN MUD WEIGHT

1821118063534438343027252322201918

Figure 2-1 Dilution Ratio Chart

2.4

hour, then 44 44 = 1 barrel ofdilution saved per hour. With thehigh cost weighted mud (usually aminimum of $30 per barrel), thesolids removal equipment would besaving at least $30 per hour. Overan average operation of 20 hoursper day, this represents a savings ofapproximately $600 per day. If themaximum amount of drilled solidswere reduced to 3%, the cost savingswould double to approximately$1200 per day.

The expense of the dilution liquidis a major factor in considering theadvantages of reduced dilutionrequirements. Oil is obviouslymuch more costly than water, butwater also can be expensive if ithas to be trucked into a remotedrilling location.

The disposal of waste mud canalso be a significant factor in overalldilution costs. Heavy reliance ondilution to control solids contentcan result in the addition of somuch extra liquid that the volumeof mud exceeds the capaci-ty of the active mud pits.When this happens, wholemud (including all of theexpensive additives) mustbe discarded into waste orreserve pits.

Appropriate use of solidscontrol equipment in placeof dilution lessens the vol-ume of the mud system andcan usually eliminate the

discarding of excess mud. The sizeof the active and waste pits them-selves can be reduced due tosmaller capacity requirements.Instead of throwing away valuablemud additives, these can be sal-vaged and returned to the activemud system.

If properly used, solids controlequipment can virtually eliminatewaste liquid mud through a closedmud system. In such a system theliquid phase can be recycled which can be critical in specialapplications such as when usingoil-base or polymer muds, especial-ly offshore, or where environmentalconcerns prohibit disposal of liquidwaste materials. In these cases thecost of hauling the liquid wasteaway for disposal is also avoided.

Solids removal by mechanical sep-aration can achieve the benefits oflow solids content and at the sametime significantly reduce the manycosts associated with dilution.

DRILLED SOLIDS

3.1

INTRODUCTION

The goal of modern solids controlsystems is to reduce overall wellcosts by prompt, efficient removalof drilled solids while minimizingthe loss of liquids. Since the size ofdrilled solids varies greatly fromcuttings larger than one inch indiameter to sub-micron size sev-eral types of equipment may beused depending upon the specificsituation. The fundamental purposefor solids removal equipment is justthat remove drilled solids. Theend result is reduced mud andwaste disposal costs.

To reach this goal, each piece ofequipment will remove a portion ofthe solids, either by screening orcentrifugal force. Each type ofequipment is designed to economi-cally separate particles of aparticular size range from the liq-uid. Also to operate effectively,each type of equipment must besized, installed, operated, and main-tained properly.

The efficiency of the solids con-trol system can be evaluated bycomparing the final volume of mudaccumulated while using the equip-ment to the volume of mud thatwould result if drilled solids werecontrolled only by dilution. The

overall results of solids removal canbe monitored by the use of flowmeters to determine the actual mudvolume built.

The efficiency of solids removalequipment and/or systems used canbe evaluated in two ways: 1) Efficiency of drilled solids

removal, 2) Efficiency of liquid conservation.

The greater percentage of drilledsolids removed, the higher theremoval efficiency. The higher thesolids fraction of the waste stream,the better. Both aspects should beconsidered.

For example, a desilter usuallydoes well at removing solids but atthe cost of significant losses of liq-uid; sometimes 80% of the volumeof the waste stream will be liquid.By contrast, a properly operatingshale shaker or centrifuge typicallyremoves 1 barrel or less of mudwith each barrel of solids. Mostremaining equipment delivers alesser degree of dryness than dothe shakers or centrifuges.

Most solids control systemsinclude several pieces of equipmentconnected in series. Each stage ofprocessing is partly dependentupon the previous equipment func-tioning correctly so as to allow thenext stage to perform its role.

3.0 MECHANICAL SOLIDS CONTROL AND RELATED EQUIPMENT

3.2

Should one piece of equipment fail,the equipment downstream willsoon lose efficiency or fail com-pletely.

The first piece of equipment usedto separate the solids from the mudis usually a vibrating screen orseries of screens. The cuttings thatare larger than the mesh openingsare removed by the screen butcarry an adhered film of mud. Thescreen mesh should be sized toprevent excessive losses of wholemud over the end screen.

The second step is to remove thesand-sized, silt sized and larger clayparticles that were not removed inthe shakers by using hydrocy-clones. Hydrocyclones with a conediameter of 6 to 12 inches arecalled desanders, and hydrocy-clones with a cone diameter of lessthan 6 inches are called desilters.These units should normally besized to process 125% of the maxi-mum flow rate used to drill.

Sometimes a screen is used belowa hydrocyclone to dry-out the

cones discharge to minimize theloss of fluid. The hydrocyclone andvibrating screen device is called amud cleaner or mud conditioner. Ifa location must be pitless, thenthe screens are essential to mini-mize the liquid waste volume.

The final step may be to removethe ultrafine silt and clay-sizedsolids with the use of a decantingcentrifuge. On a weighted mud,two centrifuges may be used inseries: the first to salvage barite, thesecond to remove fine solids andreclaim the valuable liquid phase.

3.1 PARTICLE SIZEAND CUT POINT

Modern drilling rigs may beequipped with many different typesof mechanical solids removaldevices depending on the applica-tion and requirements of a particularproject. Each device has a specificfunction in the solids controlprocess. Equipment commonly uti-lized and the effective removal rangefor each are listed in Figure 3-1.

3.3

CUT POINT

Notice the removal range, or CutPoint, is given as a range of theparticle size removed. Mechanicalsolids control equipment classifiesparticles based on size, shape, anddensity. It is typical to refer to parti-cles as being either larger than thecut point of a device (oversize) or

smaller than the cut point (under-size).

Figure 3-2 shows a typical cutpoint curve. The cut point curverepresents the amount of solids of agiven size that will be classified aseither oversize or undersize.Particles to the right of the cut pointcurve, in the area labeled A, rep-

Figure 3-1 Particle Diameter and Ideal Equipment Placement

3.4

resent the removed, oversize solids.Particles to the left of the curve, inthe area labeled B, represent theundersize solids returned with thewhole mud.

Particular interest is given to threepoints along the cut point curve,the D50, the D16, and the D84. Giventhese three points, the removalcharacteristics of screens, hydrocy-clones, or other devices can becompared.

The D50, or median cut point, isthe point where 50% of a certainsize of solids in the feed stream willbe classified as oversize and 50% asundersize. The D16 and D84 are the

points where 16% and 84%, respec-tively, of the solids in the feedstream will be classified as oversize.These two points are statisticallysignificant because they are onestandard deviation from the D50 in anormal distribution. An ideal clas-sifier (the dashed line) would showvery little difference between theD50, D16 and D84.

Separation Efficiency is a measureof the D50 size relative to the num-ber of undersize particles that areremoved or oversize particles thatare not removed. The higher theseparation efficiency, the lower the

Figure 3-2 Typical Cut Point Curve

3.5

false classification. An example willassist in understanding this concept.

Figure 3-3 shows the cut pointcurves for two screens, each withthe same D50. Curve No.1 is almostvertical with a small tail at eachend. This results in a very sharp,distinct cut point. Almost all parti-cles larger than the cut point arerejected, with very few undersizesolids. Almost all particles smallerthan the cut point are recovered,with very few oversize particlesincluded.

Curve No. 2 is an S-shaped curvewith a large tail at each end. Eventhough the D50 is the same as forCurve No.1, the D16 and D84 are very

different. Many solids larger thanthe D50 are returned with the under-size solids and many solids smallerthan the D50 are discarded with theoversize solids.

If curves number 1 and 2 inFigure 3-3 illustrate typical removalgradients for two different types ofoilfield shale shakers screens, wecan draw conclusions about separa-tion performance. The area betweenthe curves marked A representssolids Screen No.1 removes andScreen No. 2 returns. Likewise, thearea marked B represents solidsrecovered by Screen No.1, but dis-carded by Screen No. 2.

This is not to say that Screen No.1

Figure 3-3 Separation Curve

3.6

is better than Screen No. 2, orvice versa; it simply illustrates thattwo devices with similar cut point(as measured by the D50 alone) mayperform very differently. As anexample, consider solids removalfrom a weighted drilling fluid usingvibrating screens.

An effective solids control pro-gram for weighted mud shouldremove as many undesirable, sand-sized solids as practical, whileretaining most of the desirable, silt-sized barite particles. Referring backto Figure 3-3, Screen No. 2 wouldreturn all the sand in area A thatScreen No.1 would catch, andScreen No. 2 would remove the silt-size material in area B (includingall weighting material) that ScreenNo.1 would recover.

Therefore, in a weighted mud,Screen No. 2 would not perform aswell as Screen No.1. Further, if thearea to the right of both curves(representing total mass solidsremoval) were calculated, ScreenNo.1 could prove superior in termsof mass solids removal.

As shown by this example, it isimportant to view cut point as acontinuous curve, rather than a sin-gle point. This concept is equallytrue with screens, hydrocyclones,centrifuges, or any other separationequipment the relative slope andshape of the cut point curve aremore important than a single pointon the curve.

3.2 SEPARATION BY SCREENING

One method of removing solidsfrom drilling mud is to pass themud onto the surface of a vibratingscreen. Particles smaller than theopenings in the screen passthrough the holes of the screenalong with the liquid phase of themud. Particles too large to passthrough the screen are thereby sep-arated from the mud for disposal.Basically, a screen acts as a gonogo gauge: Either a particle is smallenough to pass through the screenopening or it is not.

The purpose of vibrating thescreen in solids control equipmentis to transport the cuttings off thescreen and increase the liquid han-dling capacity of the screen. Thisvibrating action causes rapid sepa-ration of whole mud from theoversized solids, reducing theamount of mud lost with the solids.

For maximum efficiency, thesolids on the screen surface musttravel in a predetermined pattern spiral, elliptical, orbital or linearmotion in order to increase par-ticle separation efficiency andreduce blockage of the screenopenings. The combined effect ofthe vibration and the screen sur-faces result in the separation andremoval of oversized particles fromdrilling mud.

3.7

SCREENING SURFACES

Screening surfaces used in solidscontrol equipment are generallymade of woven wire screen cloth,in many different sizes and shapes.The following characteristics ofscreen cloth are important in solidscontrol applications.

Screens may be constructed withone or more Layers. Non-layeredscreens have a single layer, fine-mesh, screen cloth (reinforced bycoarser backing cloth) mounted ona screen panel. These screens willhave openings that are regular insize and shape. Layered screenshave two or more fine mesh screencloths, usually of different mesh(reinforced by coarser backingcloth), mounted on a screen panel.These screens will have openingsthat vary greatly in size and shape.

To increase screen life, especiallyin the 120200 mesh range, manu-facturers have incorporated twodesign changes:1) A coarse backing screen to

support fine meshes, and2) Pre-tensioned screen panels.

The most important advance hasbeen the development of preten-sioned screen panels. Similar panelshave been used on mud cleanerssince their introduction, but earliershakers did not possess the engi-neering design to allow their usesuccessfully. With the advent ofmodern, linear-motion shakers, pre-

tensioned screen panels haveextended screen life and justifiedthe use of 200-mesh screens at theflowline. The panels consist of afine screen layer and a coarse back-ing cloth layer bonded to a supportgrid (Figure 3-4). The screen clothsare pulled tight, or tensioned, inboth directions during the fabrica-tion process for proper tension onevery screen. The pre-tensionedpanel is then held in place in thebed of the shaker.

Today, fine screens may be rein-forced with one or more coarsebacking screens. The cloth mayalso be bonded to a thin, perforat-ed metal sheet. This extra backingprotects the fine screen from beingdamaged and provides additionalsupport for heavy solids loads. Thescreens equipped with a perforatedplate may be available with severalsizes options for the perforation toallow improved performance for agiven situation.

Most manufacturers limit them-selves to one support grid opening

Figure 3-4 Pretensioned Screen

3.8

size to reduce inventory and pro-duction costs. The opening size istypically 1 for maximum mechani-cal support. Brandt / EPI providesscreen panels with a variety ofopenings to allow rig personnel tochoose the desired mechanical sup-port and total open area (translatingto more liquid flow), depending onthe application.

Mesh is defined as the number ofopenings per linear inch. Mesh canbe measured by starting at the cen-ter of one wire and counting thenumber of openings to a point oneinch away. Figure 3-5 shows a sam-ple 8 mesh screen. A screencounter is useful in determiningscreen mesh (see Figure 3-6).

SCREEN CLOTH

There are several types of wirecloth used in the manufacture ofoilfield screens. The most commonof these are Market Grade and

Tensile Bolting Cloth. Both of theseare square mesh weaves, differingin the diameter of wire used intheir construction.

Market grade cloths use largerdiameter wires and are more resis-tant to abrasion and prematurewear. Tensile bolting cloths usesmaller diameter wire and have ahigher Conductance. Since screen

Figure 3-5 Eight Mesh Screen

Figure 3-6 Screen counter and Magnified View of Screen mesh

3.9

selection is a compromise betweenscreen life, liquid capacity, and par-ticle separation, both types are inwide use.

OPENING SIZE

Size of Opening is the distancebetween wires in the screen clothand is usually measured in fractionsof an inch or microns. Figure 3-7shows a screen with a 1/2 inchopening.

Screens of the same mesh mayhave different sized openingsdepending on the diameter of thewire used to weave the screencloth. Smaller diameter wire results

in larger screen openings, with larg-er particles passing through thescreen. The larger the diameter ofthe wire, the smaller the particlesthat will pass through the screen.Remember, its the size of the open-ings in a screen, not the meshcount, that determines the size ofthe particles separated by thescreen. Also, normally the larger thediameter of the wire used in theweaving process, the longer thescreen cloth will last.

PERCENT OPEN AREA

Percent Open Area is the amountof the screen surface which is notblocked by wire. The greater thewire diameter of a given meshscreen, the less open spacebetween the wires. For example, a4 mesh screen made of thin wirehas a greater percent of open areathan a 4 mesh screen made of thickwire (see Figure 3-8).

The higher the percent of openarea of a screen the greater its theo-retical throughput. Open area can

Figure 3-7 One-half Inch Opening

Figure 3-8 Percent of Open Area

4 Mesh: .080 Wire46.2% Open Area

4 Mesh: .072 Wire50.7% Open Area

4 Mesh: .063 Wire56.0% Open Area

3.10

be increased for a given mesh byusing smaller diameter wire, but atthe sacrifice of screen life. Thechoice of any particular screen cloththerefore involves a compromisebetween throughput and screen life.

Calculating the percent open areafor layered screens is difficult andinaccurate. This is due to the ran-dom and wide variety of openingspresent. Conductance of a screen isan experimental measure of theflow capacity of a screen. The high-er the conductance of a screen, thegreater its flow capacity.

SHAPE OF OPENING

Shape of Opening is determinedby the screens construction.Screens with the same number ofhorizontal and vertical wires perinch produce square-shaped open-ings and are referred to as SquareMesh screens. Screens with a differ-ent number of horizontal andvertical wires per inch produce

oblong or rectangular shapedopenings and are referred to asRectangular (or Oblong) Meshscreens. This is illustrated in Figure3-9.

Use of a single number in refer-ence to a screen usually impliessquare mesh. For example, 20mesh usually identifies a screenwith 20 openings per inch in eitherdirection. Oblong mesh screens aregenerally labeled with two num-bers. For example, a 60 x 20 screenhas 60 openings per inch in onedirection and 20 openings per inchin the other direction.

It has become common industrialpractice to add the two dimensionsof an oblong mesh screen and referto the sum of the two numbers asthe mesh of the screen.

For example, a 60 x 20 meshscreen is often called an oblong80 mesh. This screen has oblongopenings measuring 1040 x 193microns, much larger than the

Figure 3-9 Shape of Opening

SQUARE MESH OBLONG MESH

3.11

square openings of a square 80mesh screen (177 x 177 microns).The oblong 80 will allow muchlarger, irregularly-shaped particlesto pass through its openings thanthe 80 x 80 square mesh screen.

EQUIVALENT SCREEN MESH

Screen manufacturers now com-pare different types of screenthrough charts, such as the oneshown in Figure 3-10. The oblong-mesh screens listed in the left-handcolumn remove similar sized solidsas the square-mesh screens listed inthe right-hand column. Thesescreens are referred to as equiva-lent. In actual field use, theconductance and screen life of theoblong mesh screens is noticeablyhigher than the equivalent squaremesh screen, but the shape of thecut point curve discussed earlier isnot as sharp or distinct.

In a similar fashion, a layeredscreen will often be designated bya single number, e.g. layered 210mesh. This implies a screen with

openings smaller than a square200 mesh screen (74 x 74microns). However, the actualopening size and shape of a lay-ered screen is a combination of themultiple screen layers and will pro-duce a wide variety of openingsizes and shapes. Therefore, thelayered 210 mesh screen willremove some solids smaller than 74microns, but will also allow someparticles larger than 74 microns topass through the screen openings.

SCREEN PLUGGING AND BLINDING

Screen Plugging and Blinding,while present to some degree onrig shakers fitted with coarserscreens, is most frequently encoun-tered on fine screen shakers. If themesh openings plug with near-sizeparticles or if the openings becomecoated over, the throughput capaci-ty of the screen can be drasticallyreduced and flooding of the screenmay occur.

Plugging can often be controlledby adjusting the vibratory motion ordeck angle, but sometimes requireschanging screens to a coarser orfiner mesh. A coarser screen shouldbe used only as a temporary solu-tion until the particular formationresponsible for near-size particlegeneration is passed. Changing to afiner mesh screen often presents abetter, more permanent solution.

Screen blinding is caused by

OBLONG MESH SQUARE MESH

B-20 S-16B-40 S-30B-60 S-40B-80 S-50

B-100 S-60B-120 S-80

Figure 3-10 Equivalent Screen Sizes

3.12

sticky particles in viscous mud coat-ing over the screen openings or bythe evaporation of water from dis-solved solids or from grease andrequires a screen wash-down tocure. This wash-down may simplybe a high pressure water wash, asolvent (in the case of grease, pipedope or asphalt blinding), or a mildacid soak (in the case of blindingcaused by hard water). Stiff brush-es should not be used to cleanfine screens because of the fragilenature of fine mesh screen cloth.

Screen life of fine mesh screensvaries widely from design todesign, even under the best of con-ditions, because of differences inoperating characteristics. Screen lifecan be maximized by followingthese general precautions: Keep screens clean. Handle screen carefully when

installing. Keep screens properly ten-

sioned. Do not overload screens. Do not operate shakers dry.

SCREEN CAPACITY

Screen Capacity, or the volume ofmud which will pass through ascreen without flooding, varieswidely depending on shaker modeland drilling conditions. Drilling rate,mud type, weight and viscosity, bittype, formation type, screen mesh all affect throughput to some degree.

Drilling rate affects screen capacitybecause increases in drilled solidsloading reduce the effective screenarea available for mud throughput.The mesh of the screen in use is alsodirectly related to shaker capacitybecause, in general (but not always),the finer a screens mesh, the lowerits throughput. Increased viscosity,usually associated with an increasein percent solids by volume and/orincrease in mud weight, has amarkedly adverse effect on screencapacity. As a general rule, for every10% increase in viscosity, there is a25% decrease in throughput capaci-ty. Figure 3-11 shows therelationship of mud weight, viscosity,and screen mesh on shaker capacity.

Mud type also has an effect onscreen capacity. Higher viscositiesgenerally associated with oil-baseand invert emulsion mud usuallyresult in lower screen throughput

Figure 3-11 Shaker Capacity v. Mud Weight, Viscosity, and Screen Mesh

3.13

than would be possible with a water-base mud of the same mud weight.Some mud components such as syn-thetic polymers also have an adverseeffect on screen capacity. As a result,no fine mesh screen can offer a stan-dard throughput for all operatingconditions.

Due to the many factors involvedin drilling conditions, mud charac-teristics and features of certainmodels, capacities on fine screenshakers can range from 50 to 800GPM. Multiple units, most common-ly dual or triple units, can be usedfor higher throughput requirements.Cascade shaker arrangements, withscalping shakers installed upstreamfrom the fine screen shakers, canalso increase throughput.

THREE-DIMENSIONALSCREEN PANELS

To increase screen capacity with-out increasing the size or numberof shale shakers, three-dimensionalscreen panels are available. Thedesign of these 3-D, Pinnacleshaker screens: Provides even distribution of

fluid across the screen surface Eliminates unwanted fluid loss

near the screen edges Improves dryness of solids dis-

charge Allows the use of finer screens

3-D screen panels increase the

usable screen area of a screenpanel by corrugating the screen sur-face, similar to the surface of apleated air filter or oil filter. 3-Dscreen panels are most effectivewhen installed as the submerged,feed-end screen on linear-motionshakers to take full advantage ofthe additional screen area. Past thefluid end point, a three-dimensionalscreen tends to channel thedrilled solids and increases solidsbed depth and the amount of liquidcarried off the screen surface.Using a flat screen at the dischargeend of the shaker eliminates chan-neling, increases cuttings dryness,and decreases fluid loss.

STANDARDIZATION

Standardization of screen clothdesignations has been recommend-ed by the API committee onStandardization of Drilling FluidMaterials, in API RECOMMENDEDPRACTICE 13E (RP13E), THIRDEDITION, MAY 1, 1993. The pur-pose for this practice is to providestandards for screen labeling ofshale shaker screen cloths. The pro-cedures recommended for labelingallow a direct comparison of sepa-ration potential, the ability to passfluid through a screen, and theamount area available for screen-ing.

The API screen labeling includesof the following:

3.14

1. Manufacturers designation;2. Separation Potential and3. Flow Capacity.

The Manufacturers designationcontains the individual companysprocedures for naming theirscreens. It may include the type ofscreen panel, composition andother data required by the manufac-turer.

The API separation potential isreported in the terms of three Cutpoints. The term Cut point is notthe same as the traditional cutpoint. The Cut point allows aranking of a screens separationpotential that can be used to com-pare screen performance. Threevalues (D50, D16, and D84) imply theopening sizes and variation inopening size of the screen.

Flow capacity is the rate at whicha shaker can process mud andsolids. Under constant conditions, ashale shaker has a flow capacitythat depends upon screen conduc-tance and area. The area availablefor screening is the net unblockedarea, in square feet, available forfluid passage through the screenpanel. Conductance defines theease of passage of a fluid through apiece of wire cloth. Conductance iscalculated from the mesh count andwire diameters of the screen.Transmittance is the product ofconductance times panels area.

These designations give the enduser a more accurate assessment ofsolids removal capability and liquidthroughput capacities of competi-tive screens.

3.3 SHALE SHAKERS

The first line of defense for a prop-erly maintained drilling fluid hasbeen, and will continue to be, theshale shaker. Without proper screen-ing of the drilling fluid during thisinitial removal step, reduced effi-ciency and effectiveness of alldownstream solids control equip-ment on the rig is virtually assured.

The shale shaker, in variousforms, has played a prominent rolein oilfield solids control schemesfor several decades. Shakers haveevolved from small, relatively sim-ple devices capable of running onlythe coarsest screens to the modelsof today. Modern, high-perfor-mance shakers of today are able touse 100 mesh and finer screens atthe flowline in most applications.

This evolutionary process hastaken us through three distinct erasof shale shaker technology and per-formance as shown in Figure 3-12.These eras of oilfield screeningdevelopment may be defined bythe types of motion produced bythe machines: Elliptical, unbalanced design Circular, balanced design. Linear, straight-line design

3.15

The unbalanced, elliptical motionmachines have a downward slopeas shown in Figure 3-12, A. Thisslope is required to properly trans-port cuttings across the screen andoff the discharge end. However, thedownward slope reduces fluidretention time and limits the capaci-ty of this design. Optimumscreening with these types of shak-ers is usually in the 3040 mesh(400600 micron) range.

The next generation of machine,introduced into the oilfield in thelate 1960s and early 1970s, pro-duces a balanced, or circular,motion. The consistent, circularvibration allows adequate solids

transport with the basket in a flat,horizontal orientation, as shown inFigure 3-12, B. This design oftenincorporates multiple decks to splitthe solids load and to allow finermesh screens, such as 80100square mesh (150180 micron)screens.

The newest technology produceslinear, or straight-line, motion,Figure 3-12, C. This motion isdeveloped by a pair of eccentricshafts rotating in opposite direc-tions. Linear motion providessuperior cuttings conveyance and isable to operate at an uphill slope toprovide improved liquid retention.Better conveyance and longer fluidretention allow the use of 200square mesh (74 micron) screens.

Today, shale shakers are typicallyseparated into two categories: RigShakers and Fine Screen Shakers.

RIG SHAKERS

The rig shaker is the simpler oftwo types of shale shakers. A rigshaker (also called Primary ShaleShaker or Coarse Screen Shaker)is the most common type of solidscontrol equipment found on drillingrigs. Unless it is replaced by a finescreen shaker, the rig shaker shouldbe the first piece of solids controlequipment that the mud flowsthrough after coming out of thehole. It is usually inexpensive tooperate and simple to maintain.

Figure 3-12 Shale Shakers

3.16

Standard rig shakers generallyhave certain characteristics in com-mon (see Figure 3-13): Single rectangular screening

surface usually about 4 x 5in size. Some designs have uti-lized dual screens, dual decksand dual units in parallel toprovide more efficient solidsseparation and greaterthroughput. Depending on theparticular unit and screen meshused, capacity of rig shakerscan vary from 1001600 GPMor more.

A low-thrust horizontal vibratormechanism, using eccentricweights mounted above, orcentral to, the screen basket.

Vibration supports to isolatethe screen basket from its skid.

Skid with built-in mud box(sometimes called a possumbelly) and a bypass mecha-nism.

Method of tensioning screensections.

Screen sizes commonly used withrig shakers range from 10 to 40mesh. Figure 3-14 shows the parti-cle sizes separated by these meshscreens. In this graph the area tothe left of each line representssolids which are smaller than thatmesh size. These would passthrough the screen and would notbe removed. The area to the rightof each line represents solids thatare larger than the mesh size andwould be removed from the mud.

In Figure 3-14, the area to the

Figure 3-13 Rig Shaker components

MUD TANK(POSSUM BELLY)

LIQUID and FINESOLIDS

DISCHARGECHUTE

MOTOR

BELTGUARD

VIBRATOR ASSEMBLY

COARSE SOLIDS DISCHARGE

SCREEN

BASKETASSEMBLY

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right of the 10 mesh line is con-fined, because it is limited by thesize of the page. In actual usage,this area is unlimited. This meansthat a 10 mesh screen will removeall particles larger than 1910microns it doesnt matter if theyare the size of BBs, marbles orbaseballs they will be removedand discarded by a 10 mesh screen.

Rig shakers are generally ade-quate for top hole drilling and forshallow and intermediate depthholes when backed up by othersolids control equipment. For deep-er holes and when using expensivemud systems, fine screen shakersare preferred.

FINE SCREEN SHAKERS

The fine screen shaker is themore complex and versatile of thetwo types of shale shakers. Fine

screen shakers remove cuttings andother larger solids from drillingmud, but are designed for greatlyimproved vibratory efficiency oversimple rig shakers. They are con-structed to vibrate in such a waythat they can use screens as fine as150200 mesh and still give reason-able screen life.

They are versatile pieces of equip-ment and can operate on all typesof mud. Figure 3-15 shows therange of particle sizes separated bythe screens commonly used withfine screen shakers.

A fine screen shaker can beinstalled on the rig in one of fourways:1. Instead of the conventional rig

shaker for use from top hole tototal depth, if it is of a designcapable of using coarsescreens as well as fine screens.

Figure 3-14 Particle Removal by Rig Shaker Screens

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2. Placed in series with the rigshaker by tapping into the flowline with a Y, thus keepingthe rig shaker available as ascalping shaker.

3. Replacing the rig shaker aftertop hole is completed.

4. Downstream from the rig shak-er to accept fluid after it passesthrough the coarse screenshaker (requires secondarypump).

Because fine screen shakers havea wide variety of designs, they havefew characteristics in common. Thevarious designs are differentiated byscreen orientation and shape,screen tensioning mechanism,placement and type of vibrator andother special features.

Screen Orientation and Shaperefers to the arrangement of the

screen or screens in the unit.Screens are usually rectangular andmay be single screens or multiplescreens placed in series or in paral-lel, as shown in Figure 3-16.

Single deck, single screens (Figure3-16 A & B) are the simplest design,with all mud passing over onescreen of uniform mesh. This typeof shaker requires efficient vibratormechanisms to function properlyunder all possible drilling condi-tions and requires high throughput(Conductance) per square foot ofscreen cloth.

Units with screens placed in par-allel (Figure 3-16 C, D & E) havetwo or more screen sections actingas one large screen so that no cut-tings can fall between them. Allscreen sections should be the samemesh, since the coarsest mesh sec-tion determines the units screeningability.

Figure 3-15 Fine Screen Shaker Particle Separation

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Shakers with screens stacked inseries (Figure 3-16 F) have a coarsescreen above a finer screen, with thefiner screen being the controllingmesh size. The operating theory isthat the top screen will removesome of the cuttings from the mudto take part of the load off the bot-tom screen and thereby increaseoverall screening efficiency.

SCREEN TENSIONING MECHANISMS

Shakers are designed to use eithera hookstrip or a rigid panel screen.Hook strip screens are made with-out a rigid frame and canprematurely fail if installed andallowed to operate with uneventension. The shaker manufacturersinstructions for screen installationshould be followed, but the follow-ing steps may apply: Inspect the supports and ten-

sion rails to be sure they are ingood condition and clean

Position the panel on the deckand inspect the screen to besure it lays flat

Install both rails loosely to thehookstrip

Push one side of the screenagainst the positioning blocks,if present; and fully tighten thescreen against these blocks

Evenly tighten the tension boltson the other side

Torque to the manufacturersrecommended setting

Rigid panel screen installationshould proceed as per the manufac-turers instructions. Panel screenscan usually be installed or replacedmuch quicker than a hookstripscreen since the cloth is alreadypretensioned and the mechanicaldevices lock the panel with muchless manual effort.

Figure 3-16 Shaker Screen Configurations

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VIBRATOR MECHANISMS

Vibrator Mechanisms vary widelyin design and placement and great-ly affect the throughput efficiencyof fine screen shakers. Most mod-ern shakers utilize linear motionvibration with the vibrator mecha-nism mounted above the screenbed. One important advantage oflinear motion is positive con-veyance of cuttings across thescreen surface even when the sur-face is at a positive angle. Thisgenerally allows the use of anuphill sloped screen deck, greatlyincreasing throughput capacity andcuttings dryness.

Most vibrators are electricallyoperated, although a few arehydraulically operated. In someunits the vibration-inducing eccen-tric weights are separated from thedrive motor, while in others theeccentric weights and motor forman integral assembly. In some units,the nature of the vibratory motionscan be easily modified to takeadvantage of specific solids-convey-ing characteristics, but most unitshave a fixed vibratory motion.

MAINTENANCE

Because of their greater complexi-ty and use of finer mesh screens,fine screen shakers generallyrequire more attention than rigshakers. Nonetheless, their moreeffective screening capabilities

more than justify the higher operat-ing cost. This is especially truewhen expensive mud systems areused.

Besides periodic lubrication, finescreen shakers require the sameminimum maintenance as rig shak-ers while making a trip: Wash down screens. Check screen tension. Shut down shaker when not

drilling to extend screen life. Dump and clean possum belly.

In addition, frequent checks mustbe made for screen plugging andblinding, screen flooding and bro-ken screens. All will occur morefrequently on fine screen shakersthan on coarse mesh rig shakers.

GENERAL GUIDELINES

General rules in operating shaleshakers whether coarse screenrig shakers or fine screen shakers which have not already beenmentioned, include the following: Use the finest mesh screen

capable of handling the fullvolume from the flow lineunder the particular drillingconditions. This will reducesolids loading on downstreamhydrocyclones and screens,improving their efficiency.Several screen changes, nor-mally to progressively finermesh screens over the course

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of the hole, are quite common. Large cuttings which settle in

the mud box (possum belly) ofthe shaker should never bedumped into the mud system.(Dump them into the sump orwaste pit.)

Except in extenuating circum-stances (such as the presenceof lost circulating material), allmud should be screened. Thisincludes make-up mud hauledin from other locations.

Unless water sprays areabsolutely necessary to controlscreen blinding, water shouldnot be used on the screen sur-face while drilling. Watersprays tend to wash smallercuttings through the screenwhich would otherwise beremoved by their clinging tolarger particles (piggy-backeffect).

For a more complete analysis ofdifferent types of screens and shak-ers, ask your local Brandt / EPIrepresentative for copies of the lat-est Product Bulletins.

3.4 MUD CLEANERS ANDMUD CONDITIONERS

In many cases, combinations ofvibratory screening and settling/centrifugal force are used togetherto provide an effective separation.The most familiar combination sep-

arator is the Mud Cleaner or MudConditioner (Figure 3-17).

Mud cleaners were developed inthe early 1970s to remove finedrilled solids from weighted mudwithout excessive loss of barite andfluid. They have also proved valu-able tools in closed systems andother dry location applications.These devices use a combination ofdesilting hydrocyclones and veryfine mesh vibrating screens(120400 mesh) to remove finedrilled solids while returning valu-able mud additives and liquids backto the active mud system.

Traditional mud cleaners use mul-tiple 4 or 5 cyclones, mountedover a vibrating screen, and areable to effectively process 400600GPM. The process capacity is limit-ed by screen capacity and its abilityto discard dry solids. With theintroduction of linear motion vibrat-ing screens, the capacity of themud cleaner screen has been great-ly increased. This, in turn, allowsthe use of additional hydrocyclonesand higher, overall process capaci-ties.

The combination of hydrocy-clones and linear-motion vibratingscreens is called a Mud Conditionerto differentiate these machines fromearlier mud cleaners. Mud condi-tioners often combine bothdesander and desilter cones mount-ed above the screen deck to take

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full advantage of the higher processcapacity, usually 10001500 GPM,and reduce the overall size andweight of the unit, when comparedto mud cleaners.

After removal of large cuttingswith a shaker, feed mud is pumpedinto the mud cleaner/conditionershydrocyclones with a centrifugalpump. The overflow from thecyclones is returned to the mudsystem. Instead of simply discardingthe underflow, the solids and liquidexiting the bottom of the cyclonesare directed onto a fine screen.Drilled solids larger than the screenopenings are discarded; the remain-ing solids, including most barite ina weighted system, pass throughthe screen and are returned to themud system.

The cut point and amount of masssolids removed by a mud cleaner/conditioner depends primarily onthe mesh of the fine screen used,Figure 3-18. Since there are manydesigns of mud cleaners/condition-ers available, performance andeconomics will vary with machineand drilling variables.

APPLICATIONS

Mud cleaners/conditioners shouldbe considered in these applications:1. Whenever the application

requires finer screens than theexisting shaker can handle

2. Unweighted OBMFigure 3-17 Mud Cleaners and Mud Conditioners

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3. Expensive polymer systems4. When the cost of water is high5. Unweighted WBM with high

disposal costs and/or environ-mental restrictions

6. When use of lost circulationmaterial requires bypassing theshaker

7. Workover and completion fluid

Mud cleaners/conditioners aresimply a bank of hydrocyclonesmounted over a fine-mesh screen.In many instances (even with mod-ern fine screen shakers), a finerseparation is required than can beprovided with existing shakers. The

question to answer becomes howto achieve the necessary level ofscreening at the lowest cost. Thealternatives are:

1) Add additional similar shakersto handle the flow rate, 2) Replacethe existing shakers with more effi-cient units or 3) Add a mudcleaner/conditioner downstreamfrom the existing shakers.

Any of these may be correct, buta thorough study of the capital cost(the actual cost of new equipment,plus transportation, rig modifica-tions, and installation) and theoperating cost (screens and otherexpendables, plus fuel) is necessary

Figure 3-18 Particle Removal by Mud Cleaner Screens

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to make the proper choice. Also,because of the cut points producedby some modern layered screens,the use of mud cleaner/condition-ers may be indicated downstreamof linear motion shakers.

Salvage of the liquid phase of anunweighted drilling mud often cost-justifies use of a mud cleaner/conditioner when the fluid phase ofthe mud or disposal is expensive.Compared to desanders and desil-ters, whose cyclone underflow maybe as much as 15 bbl/hr or more,mud cleaners/conditioners canachieve efficient solids removalwhile returning most liquid back tothe active mud system. Use of ultra-fine screens (200 to 325 mesh)significantly improves solids controlin any high-value fluid system.

An increasingly important applica-tion of mud cleaners/conditioners isthe removal of drilled solids fromunweighted water-base mud insemi-dry form. This system is com-monly used in areas whereenvironmental restrictions prohibitthe use of earthen reserve pits, andexpensive vacuum truck waste dis-posal from steel pits is thealternative. The mud cleaner/condi-tioner is used to discard drilledsolids in semi-dry form which isclassified as legal landfill in mostareas and is subject to economicaldry-haul disposal techniques (dumptruck or portable waste containers).

When used for this purpose, thescreen underflow from the mudcleaner/conditioner is often divert-ed to a separate steel waste pit forvacuum truck disposal. This mayseem counterproductive, but sincea vacuum truck can only carry alimited amount of sand because ofthe over-the-road weight restric-tions, whenever a vacuum truckmust haul normal full-flow desilterwaste, the waste must be dilutedwith rig water to reduce density.The operator is then billed for thehaulage of a vacuum truck loadcomprised largely of rig water. Onthe other hand, since most of thesolids are removed in semi-dryform by the mud cleaner/condition-er screen, the remaining solids inthe screen underflow are diluteenough to be hauled away withoutwatering them back. Vacuum truckloads often can be reduced to asmall fraction of those requiredwith full-flow desilting.

This approach to dry-solids dis-posal can be carried further byusing a centrifuge with a mudcleaner/conditioner to form aclosed system which eliminatesdiscarding of any fluid. These sys-tems are being used increasingly inareas where liquid mud waste mustbe hauled a significant distance andis subject to a high disposal fee.

In a closed system, underflowfrom the mud cleaner/conditioner

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screen is diverted to a holding tankand then centrifuged, which resultsin disposal of very fine, semi-drysolids and return of liquid to theactive system. Such a system virtu-ally eliminates the need for reservepits, minimizes dilution, eliminatesvacuum truck services for disposalof liquid mud, and meets environ-mental constraints when drillingwithin ecologically sensitive areas.

One special mud cleaner/condi-tioner application is the use of adouble-deck unit for salvage ofcoarse lost circulation material(LCM). Usually when running LCM,the shale shaker is bypassed anddrilled solids build up rapidly in themud, necessitating a high level ofdilution and new mud. Use of atwo-deck mud cleaner/conditionerallows salvage of the LCM whileminimizing the increase in solidscontent.

Within the mud cleaner/condi-tioner, a coarse top screen is usedto pre-screen the mud and removethe lost circulation material. Thismaterial is discharged back into theactive system for recirculationdownhole. The drilled solids, mudadditives and liquid phase passthrough the top screen onto thelower, finer mesh screen, where thedrilled solids are separated out anddiscarded. The cleaned mud thenflows back into the mud systemand is re-blended with the salvaged

lost circulation materials.Another mud cleaner/conditioner

application is the clean up ofworkover and completion fluids. Inorder to reduce costs associatedwith this expensive task, a mudcleaner running one or two ultra-fine screens (200 over 325 mesh)can be used to remove most of thesolids before they reach cartridgetype filters.

This application can significantlyreduce filter replacement costs,reduce downtime in changing fil-ters, and allow larger volumes offluid to be cleaned at a faster rate.

INSTALLATION

Installation of the mudcleaner/conditioner is made down-stream of the shale shaker and thedegasser. The same pump used tofeed the rigs desander or desilter isoften reconnected to feed the mudcleaner/conditioner when weightmaterial is added. (Most mud clean-er/conditioners are designed to alsofunction as desilter on unweightedmud by rerouting the cone under-flow or by removing or blanking offthe screen portion of the unit. Themud cleaner/conditioner may thenbe used to replace or augment therigs desilter during top holedrilling.)

Follow these guidelines wheninstalling mud cleaner/conditionersto allow peak efficiency:

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Size the mud cleaner/condi-tioner cyclones to process110125% of the full circulatingflow rate.

Take the mud cleaner/condi-tioner suction from thecompartment receiving fluidprocessed by the degasser(Weighted Muds).

When using mud conditionersthat have both desander anddesilter cones, use a separatefeed pump for the desandercones and another feed pumpfor the desilter cones. Thedesander cone suction shouldbe from the degasser dischargecompartment. The desiltercone suction should be fromthe desander discharge com-partment.

Keep all lines as short andstraight as possible.

Install a guard screen withapproximate