7 - Lost Circulation_PTM_Handout

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SCOMI OILTOOLS

Global Research & Technology Centre/ GRTC

Training Department

LOST CIRCULATIONLOST CIRCULATIONLOST CIRCULATIONLOST CIRCULATION

SCOMI OILTOOLS

Lost Circulation

• Partial or Total loss of whole drilling fluid to the formation

• Occurs at any depth

• Occurs in almost all types of formation

• One of the major problems in drilling for hydrocarbons

• Associated with high cost and high risk

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Undesirable Effects of Lost Circulation

• Lowering of the mud level in the annulus

• Hydrostatic Pressure < Formation pressure

• Increase in costs

• Fighting Mud Losses

• Loss of Lithological information

• No drilled cutting return to surface

• Stuck Pipe

• Leads to expensive fishing jobs

• Reduced Well Productivity

• LCM entering potential pay zone

• Possibility of Sidetracking

• Possibility of losing the hole

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Types of Lost Circulation Zones

• Four main formation types which losses occur

• Unconsolidated or Highly Permeable (Matrix losses)

• Naturally Fractured

• Induced Fractured

• Cavernous

• Four types of loss rate

• Seepage losses < 25 WBM or 10 OBM bbls/hour

• Partial losses 25 – 100 WBM or 10 – 30 OBM bbls/hour

• Severe losses > 100 WBM or > 30 OBM bbls/hour

• Complete losses No returns to surface

Classification will vary by Operator

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Unconsolidated & High Permeability

Formations

• Horizontal beds at shallow depths

• Formations can be gravel beds, sand,sea shells or combination of these

• Typical losses are slight, but can worsendramatically

• Keep hole full by filling from top

• Cures

• Reduce hydrostatic / Foam Drilling

• Apply proper of LCM types and sizes

• Cement Plugs

SCOMI OILTOOLS

Naturally Fractured Formations

• Usually occur at greater depth

• Either Horizontal or Vertical fractures

• Horizontal fractures usually above 2500 ft

• Vertical fractures usually below 2500 ft

• Fractures more common in areas oftectonic activity

• Commonly associated with limestone,dolomite, chalk, hard sands, hard shale

• Initial losses are often slight

• Cures

• Reduce Hydrostatic / Foam Drilling

• LCM Pills

• Cement Plugs

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Induced Fractured Formation

• Occur at any depth (Horizontal < 2500ft, Vertical > 2500 ft) and any type offormation

• Usually associated with weak beddingplanes

• Often results from sudden surges againstthe formation

• Running casing too quickly

• Pumping too quickly

• Gel Strengths too high

• Mud weight too high

• Losses are normally sudden andcomplete

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Cavernous Formations

• Associated with Limestone and Dolomite• Losses are usually sudden and complete• Pressures are normally subnormal

• Lower than hydrostatic• Most difficult loss zone to cure• Cures

• Case-off zone• Limited success with conventional techniques

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SCOMI OILTOOLS

Mechanics of Lost Circulation

• Hydrostatic pressure exceeds formation pore pressure• Mud is forced into the zone• Mud is lost through the pore spaces in loose sand/gravel

• Unrestricted entry into formations• Cavernous formations• Loss rate will exceed pump rate

• Hydrostatic pressure exceeds formation fracturepressure• Fracture will continue to extend until

• Pressure at fracture tip < Fracture propagationpressure

• The hydrostatic drops below formation fracturepressure

SCOMI OILTOOLS

Mechanics of Lost Circulation

• Vertical Fractures

• Limited in height by boundaries

• LCM tends to settle on low side

• Horizontal Fractures

• Limited height due to overburden

• LCM more likely to succeed

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Preventing Lost Circulation

Well planning and mud program preparation should considerall aspects of avoiding lost circulation:

• Offset well data – did they have losses – why - what LCMworked or did not work

• Casing setting depths for current well• Which contingency LCM to have on rig and onshore asbackup

• What pills to pump and how to spot them• Should LCM pills be premixed – necessary in some areaswhere losses pose serious well control issues

• Prepare LCM Decision Trees

“PREVENTION IS BETTER THAN CURE”“PREVENTION IS BETTER THAN CURE”

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• Minimize the hydrostatic pressure to the lowest safelevel

• Optimize the mud properties (minimise ECD)• Viscosity• Yield Point• Gel Strengths

• Maximize BHA clearance• Minimum number of reamers, stabilizers, etc.• Avoid oversized stabilizers• Drill-pipe rubbers must not swell

“PREVENTION IS BETTER THAN CURE”“PREVENTION IS BETTER THAN CURE”

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• Minimise Swab and Surge Pressures

• Reduce tripping speeds for casing or drill-pipe

• Break circulation cautiously

• Using the lowest pump rate necessary

• Maintaining optimum mud properties

• Control the Drilling Rate

• Drilled cuttings should not exceed 5% by volume

• Avoid mud rings and bit balling

• Solids Control Equipment Optimization

• Controls filter cake thickness

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• Extra casing string or better choiceof casing points• Loss zones not subjected to highmuds weights

• Air, Foam or Aerated Mud Drilling• Hydrostatic pressure reduction

• Blind Drilling• Drill loss zones prior to treatment• Not possible if water is scarce• Risk of sticking the drill string• Well control problems

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• Drilling not Spudding Bridges

• Increase in ECD

• Use of Inhibitive Muds

• Prevent clay hydration and squeezingformations

• Pre-treat system with 5 - 10 ppb LCM

• Reduce changes of losses in known loss zones– e.g. calcium carbonate as bridging agents

• Current Database with up to date records

• Assists in planning on future wells


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Location of Lost Circulation Zones

There are four main methods of depth determination

• TEMPERATURE SURVEY

• RADIOACTIVE TRACER SURVEY

• HOT WIRE SURVEY

• SPINNER SURVEY

These are rarely used – zones normally determined by prior experience or ‘best feel’ for what is happening downhole

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SCOMI OILTOOLS

Conventional Lost Circulation Materials/LCM

Fibrous Materials Flake Materials Granular Materials

Raw Cotton Mica Nut ShellsWood Fibre Cellophane Nut hullsBark Fibre Cork Rice hullsTextile Fibre Corn cobs WoodMineral Wool Cotton seed Corn cobsStraw Plastics AsphaltAsbestos Ground RubberLeather SaltPeat Moss BentoniteFeathers Limestone/CaCO3Flax Perlite

SCOMI OILTOOLS

Lost Circulating Materials/LCM

Scomi Oiltools continues to treat LC events casually and without muchthought to selection of material or size. The most effective LCM havebeen identified as:

• API barite - excellent LCM up to opening size of 150-200 microns• Calcium carbonate - ranges of sizes extending from 0.1 micron to1 mm

• Synthetic graphite (Hydro-Seal) when used in barite weightedmuds

• Fine grind synthetic graphite (Hydro-Seal F) with d50 ofabout 100 microns for special applications

• Ground nut hull (nut-plug) - fine grind material with d50 of 350 -450 microns.

• Ground carbon (petroleum coke) - size ranges with d50 of about100 microns and 300 microns

LCM larger than 1 mm is ineffective and increases circulating losses

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SCOMI OILTOOLS

Lost Circulating Materials/LCM

• Key engineering staff at Shell, Conoco-Phillips, Shell, BPand ExxonMobil helped established these guidelines.

• Fibers, flakes, rubber, mica should generally be avoidedexcept in vuggy formations.

• The concept was taught in patents written by Conoco,BP, Halliburton (Superior Graphite), and in definedengineering practices of Shell, BP, ExxonMobil,ConocoPhillips, Halliburton, Miswaco, where thistechnology has been employed by Scomi (Pakistan,certain Malaysian jobs, Thailand) the results have beenpredictable and virtually always successful.

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Selecting the Bridging Particles

• Bridge must to be sealed to prevent leakage of fluid into the fractures which could grow the fracture

• Estimate the fracture width

• Select “strong” particles such as marble, large enough to bridge the fracture mouth

• Largest pore throat of unsealed bridge is approximately 1/3 to ¼ the fracture aperture

• Use a smooth size distribution that range from < 1 micron to the fracture width

• Consider particle already in the base fluid

1 micron

Clay fine

BASE MUD BRIDGING SOLIDS

Frac width50 microns

barite

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Losses to High-Permeability Sands

• A properly bridged reservoir composed of relatively highporosity sand cannot be fractured. To achieve thischaracteristic, selection of particle size is critical anddepends upon the grind of barite or calcium carbonateselected to meet requirements for mud densityand formation pore size distribution

• For bridging of barite weighted muds a calciumcarbonate with d50 of 200 to 300 microns.

• Fine grind "nut plug" is also very useful if ground tointernational specs with range of about 75 - 1000microns with d50 of about 400.

SCOMI OILTOOLS

Losses to Low-Permeability Sands and Shale

• Same sort of bridging materials as previously described (losses to high permeability sand) in barite weighted muds.

• This range of calcium carbonate provides a bridge for barite and mud cake to build a seal.

• Fibrous material will not properly and will generally not stop fracture charging.

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SCOMI OILTOOLS

Losses to fixed fractures

• 90% of fixed fractures to which barite weighted mud is lost can be best sealed with the same material as described previously (losses to high permeability sand).

• Un-weighted muds will require an expanded range of calcium carbonate size.

SCOMI OILTOOLS

Losses to Vuggy Zones

• Vuggy limestones are a different issue. If deep, it islikely that the vugs have collapsed and LCM asdescribed previously will be effective.

• If Vertical Stress is less than the unconfinedcompressive strength of the limestone, then vugs willremain open and can be of virtually anysize. Shredded wood, fibers, flakes, mica, oranything else will probably help!

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SCOMI OILTOOLS

Field Application

BY PASS Shakers?

� Reuse materials

� Less materials

� Less works to add

� Less waste

� Can be premixed at plant

� Particle grinds down

� High rheology

� Sand stay in the system

� Wear on pump liners

� Wear on LWD

� Must replace ground down particles

RECOMMENDED FOR SHORT INTERVAL ONLY

Screen-out of system?

� More control on size in the system

� Rheology more easily controlled

� Sand removed from system

� Less wear on pump liners

� Less wear on LWD

� Use more materials

� More work to add

� More waste materials

� More inventory on deck

� Contamination of cutting with CaCO3

RECOMMENDED FOR LONGINTERVAL OF APPLICATION

SCOMI OILTOOLS

Lost Circulation Response

This will vary from operator to operator and from field to field.

• Response may depend on various factors:-

• Are there enough chemicals / mud stocks

• Can we continue to drill with the loss rate until we can set casing

• Does well control allow us to drill with losses or lower the mud weight

• Pre planned Lost Circulation Decision Trees will aid response – based on experience on offset wells – 2 examples follow

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SCOMI OILTOOLS

Precautions During Losses

• Keep the hole full at all times to avoid well control problems.

• The pipe should be moved continuously to avoid getting stuck.

• Order mud chemicals and LCM as soon as losses become evident.

• Ensure you are informed as soon as losses are detected.

• Keep a minimum contingency of LCM material to avoid delays.

SCOMI OILTOOLS

Lost Circulation Response

• < 25 WBM or < 10 OBM BPH: • Continue Drilling (can you live with the losses)• Reduce pump rate• Pump LCM pill

• 30 - 100 WBM or > 10 OBM BPH :• Reduce pump rate immediately• Pump LCM pill• Continue with LCM pills till cured

• > 100 WBM or > 30 OBM BPH (and complete losses)• Stop drilling• Spot LCM pill, observe well• Keep annulus full of water or base oil if well control considerations allow

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SCOMI OILTOOLS

Severe and Complete Loss Circulation Cures

• Cement

• Cheap

• Composition can vary

• Weight

• Setting Time

• Filter Loss

• High Filter Loss Slurries

• Mixture of Attapulgite, Lime and various bridging agents

• Only Pump Acid or Water Soluble Materials in the Reservoir

SCOMI OILTOOLS

Severe and Complete Loss Circulation Cures

Gunk Plugs• Diesel Oil Bentonite (DOB)• Diesel Oil Bentonite and Cement (DOBC)

• Set on contact with water• Bridging agents can be added if required

DOBDOB

50 BBL diesel / base oil50 BBL diesel / base oil300 ppb 300 ppb bentonitebentoniteBarite if requiredBarite if required

ProcedureProcedure

Squeeze 50 Squeeze 50 -- 100 psi100 psiHold for 1 hourHold for 1 hourWait further hour beforeWait further hour beforedrilling out.drilling out.

DOBCDOBC

50 BBL diesel / base oil50 BBL diesel / base oil200 ppb bentonite200 ppb bentonite94 ppb cement94 ppb cementBarite if requiredBarite if required

ProcedureProcedure

Squeeze 50 Squeeze 50 -- 100 psi100 psiHold for 1/2 hourHold for 1/2 hourWOC 4 WOC 4 -- 8 hours before8 hours beforedrilling out.drilling out.

Mixing sub for DOB/C Plugs

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SCOMI OILTOOLS

Selection of Bridging Particle Size Summary

• No more Fine, Medium and Coarse

• In most cases the primary bridging and lost circulationmaterial is API Barite

• API Barite will plug large pores and fractures up to 150microns or about 6/1000 inch

• Total loss of returns can occur to a fracture of only 250– 750 microns

• When drilling with a barite weighted mud, theoptimum size range for an additional bridging materialis close to :

• 10% less than 100 microns



SCOMI OILTOOLS


• The optimum distribution can close and seal fractureand vugs off up to 2 milimeters

• Sealing studies have shown that requirement forconcentration of bridging material varies with thesquare of the increase in fracture width. If 10 lb/bbls isrequired fro 250 micron fracture, then 40 lb/bbls isrequired for a 0.5 millimeter fracture, and 160 lb/bblmay be required for a 1 millimeter fracture.

• Fractured of less than 1.5 to 2.0 mm may be controlledby bridging material carried in the mud system. Forlarge fracture width, high solids pills may be necessary.

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SCOMI OILTOOLS


• Bridging material greatly exceeding the fracture width isineffective and will interfere with development of a sealand closure

• Bridging material similar in size to the barite alreadyused in the mud system is generally useless.Discontinue recommendation for calcium carbonate ofless than50 microns for sealing fractures.

• For bridging, sealing, closure of induced and naturalfractures less than 2 mm rely on standard sized resilientgraphite, ground calcium carbonate, properly sizedclean hard nut hull, or ground petroleum coke.

SCOMI OILTOOLS


• Never use platy, fibrous or roundly spherical materials. Softresilient material such as rubber and plastics are much lesseffective than hard materials.

• When massive losses are not expected to induced fracture,“fine grind” synthetic graphite may also be useful. HYDRO-SEAL G Fine ia a ½ sized material which will largely pass 60mesh shaker screens for more economical less demandingapplications.

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SCOMI OILTOOLS


• Filtration control is important when drilling relativelyimpermeable clastics for wellbore strengthening to occur.HTHP values of less than 2 ml are typically specified. An HTHPof less than 1 ml would be better ifit can be achieved whendrilling impermeable clastics.

• Filtration control is less important when drilling highlypermeable rock

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• If losses are expected to induced fractures when drillingreservoir rock, supplemented bridging agent material must bein place before losses occur, especially when drilling with oilor synthetic based mud.

• Damage to formation may be eliminated

• Damage to production screens on flow back will beprevented

• A few pounds of graphitic bridging material is likely muchless damaging than 100 barrel of whole mud loss toreservoir rock.

• 100 barrels of whole mud flowing back with produced sandcan plug and collapse an entire screen section.

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SCOMI OILTOOLS

EZ SqueezeEZ Squeeze

SCOMI OILTOOLS

Description and Specifications

Description :

• E Z Squeeze is a high fluid loss, high solids slurryand its performance is unique to other type of LCM.Solid plug is formed within the loss zone whenliquid phase is squeezed from slurry

Applications :

• Open hole remedial lost circulation squeeze• Open hole preventative lost circulation squeeze• Cased hole squeeze for sealing perforations orcasing leaks.

•38

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SCOMI OILTOOLS

Benefits

Benefits :

• Solves lost circulation problems

• Eliminates risk of side-tracking hole (as can occur with cement)

• Does not contaminate drilling fluids

• Less costly than mixing and pumping pill after pill of conventional LCM

• Compatible with all water-base, oil-base and synthetic-base muds.

• Can be pumped through MWD’s and LWD’s.

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SCOMI OILTOOLS

E Z SQUEEZE

The type of filter cake deposited by an E Z Squeezeand conventional drilling slurry. This is indicative ofthe type of plug that will form in the lost circulationzone.

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Key Factors

There are two key factors to obtaining a successful E ZSqueeze:

1. a slurry with an extremely high solids content and high fluid loss must be prepared.

2. the slurry must be placed at the proper location in the wellbore.

SCOMI OILTOOLS

How does EZ SQUEEZE Work1) Squeezing the EZ Squeeze from drill string into the loss circulation zone

2) As the mud is pumped behind the EZ Squeeze, the fluids is squeezed out creating a bed of solids in the loss zone

3) The Solids Bed begins to build - The fluids continues to flow through the solids without forcing them into the loss zone

4) The mud begins to build a wall cake against the solids bed. Continued squeeze pressure causes the mud filter cake to compress the solids bed tightening the seal

5) Once the squeeze pressure is obtained, the EZ Squeeze hardens in place, forming a near permanent seal

EZ SQUEEZE MUD FLUID SOLID BED MUD CAKE

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How does EZ SQUEEZE Work

As the mud is pumped

behind the EZ Squeeze,

the fluids is squeezed

out creating a bed of

solids in the loss zone

The Solids Bed begins to

build.

The fluids continues to

flow through the solids

without forcing them into

the loss zone

Squeezing the EZ

Squeeze from drill

string into the loss

circulation zone

EZ SQUEEZE MUD FLUIDS SOLIDS BED MUD CAKE

SCOMI OILTOOLS

The mud begins to build a wall cake

against the solids bed. Continued

squeeze pressure causes the mud

filter cake to compress the solids bed

tightening the seal

Once the squeeze pressure is

obtained, the EZ Squeeze

hardens in place, forming a

near permanent seal

EZ SQUEEZE MUD FLUIDS SOLIDS BED MUD CAKE

How does EZ SQUEEZE Work

Documents

7 - Lost Circulation_PTM_Handout