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© 2006 PetroSkills LLC, All Rights Reserved
DRILLING FLUIDDRILLING FLUID
The drilling fluid is a large The drilling fluid is a large and important part of the and important part of the
drilling operationdrilling operation
2 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Historical perspectiveHistorical perspective1901 – The Spindletop well introduced
rotary drilling methods and drilling fluid1920’s – Barite was first used for
densityOther additives and systems followed:
Bentonite Polymers Oil-based systems
3 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Air, natural gas or nitrogen-based systems
1970’s – Safety and environmental issues in addition to performance and cost
1990’s – Synthetic based muds now called non-aqueous drilling fluids or NADF
4 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Major Major factors in factors in drilling drilling fluid fluid selectionselection
EconomicsEconomics
PerformancePerformance
Health, Safety, EnvironmentHealth, Safety, Environment
Risk AssessmentRisk Assessment
5 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Function of drilling fluid or mudFunction of drilling fluid or mudRemove cuttings from the holeClean bottom of the hole (below bit)Prevent flow of formation fluidsControl torque (reduce friction)Retard corrosionDeposit a thin filter cakeTransmit MWD information
6 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Economically deliver a wellbore suitable for formation evaluation and completion
Prevent change in hole sizeAid in cement placementPrevent lost circulationMinimize formation damageAssist in formation evaluation
7 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Drilling fluids cannot do Drilling fluids cannot do everythingeverything
Must decide on prioritiesMust decide on prioritiesNumber one function is to clean holeIf you do not clean the hole, you
cannot drill
8 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Symptoms of poor hole cleaning Excessive torque Drag on connections Tight hole and bridges on trips Fill on bottom
Adjust annular velocity and mud viscosity to increase lifting capacity
Will cover lifting capacity after drilling fluids
9 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Number two is to prevent blowouts
Blowouts can be catastrophic with loss of life, equipment and environmental damage
The most common additive for density is barite
10 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid
Weight Specific Average Average ChemicalMaterial Gravity Density, ppg lbs/bbl Formula
Barite 4.2 35.0 1470 BaSO4
Hematite 5.2 43.3 1819 FeO.Fe2O2
Ilmenite 4.8 40.0 1680 TiO2.FeO
Hematite and Ilmenite are not used very often in drilling fluids
Only for very high density drilling fluids
11 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Bottomhole cleaning is primarily performed by the hydraulics and not the mud Mud additives generally reduce bottomhole
cleaning Bit balling is less of a problem with
dispersed mud systems
12 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
In most instances, hole lubrication is not a requirement It does become critical in extended reach
wells, some horizontal wells and some directional wells
A good bentonite content and low drill solids content will yield lower friction coefficients
Oil muds will usually yield the lowest friction coefficients but not always
13 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Adding oil to the mud can reduce the friction coefficient
Specialty fluids containing fatty acids, complex alcohols and mineral oils are used to reduce torque and drag
All these things will influence other mud properties and must be considered
14 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Protect formation productivity and assist in formation evaluation is a noble aim for the mud system All drilling mud is damaging to some extent,
if not, it is called lost circulation The question is whether the damage can
be reversed or limited to near the wellbore
15 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Formations that will be cased, cemented, perforated and fracture stimulated may not present a problem with formation damage
Formations that will be completed with screens, pre-packed screens or gravel pack may have more problems with near wellbore damage
16 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Retard corrosion Corrosion is reduced by maintaining a pH
above 8.5 to 9.0 A common additive to increase the pH is
caustic (NaOH) Potassium hydroxide can also be used
(KOH) Corrosion inhibitors or oxygen scavengers
can be used to improve corrosion resistance
17 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
H2S and CO2 are acid gases When mixed with water based mud, they
lower the pH and promote corrosion H2S is deadly in small quantities and should
be treated immediately H2S can cause hydrogen embrittlement in
high strength carbon steel CO2 will flocculate the clays and cause
severe viscosity problems
18 © 2006 PetroSkills LLC, All Rights Reserved
Drilling FluidDrilling Fluid
Assist in cementation Very few drilling muds assist in
cementation Typically mud hinders the displacement of
the cement and a lot of the additives will retard the cement
Thin filter cakes help reduce the potential for differential pressure sticking and can help reduce torque and drag
19 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
AirAir
WaterWater
Water based Water based mudmud
Oil based mudOil based mud
Synthetic based Synthetic based mudmud
Types of Drilling Fluids
Air Water Oil Synthetics
Fresh Saline Diesel Mineral
Sea Water Saturated Salt KCl
20 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
AirAirDrills faster than any other drilling
fluidCan only be used in harder rock with
lower production ratesNo control of formation pressure
21 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
WaterWaterWater drills better than drilling fluids
with solidsLow density, no solids, low viscosityNot all formations can be drilled with
water
22 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Water based mudsWater based mudsClay for viscosity Barite for densityChemicals and polymers to get
desired propertiesDrill solids as a contaminant
23 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Water based muds can be broken Water based muds can be broken down into fresh water or brine down into fresh water or brine systemssystems
Fresh water muds are by far the Fresh water muds are by far the most common drilling fluids in the most common drilling fluids in the worldworld
They can be anything from water They can be anything from water and drill solids to complex mudsand drill solids to complex muds
24 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Brine systems or salt water Brine systems or salt water muds are specialty muds used to muds are specialty muds used to obtain a specific objectiveobtain a specific objective
The book presents some of the The book presents some of the advantages and disadvantages advantages and disadvantages of salt mudsof salt muds
25 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
ADVANTAGESADVANTAGES DISADVANTAGESDISADVANTAGESMay be cheapest alternative in off-shore locations
May create disposal problem in some areas
Can result in better hole stability than fresh water counterpart
Usually requires more chemical treatment than fresh water mud
Salt saturated systems offer potential of highest possible densities
Often more expensive than equivalent fresh systems
Resistant to contamination by gypsum bearing zones
Poor filter cake properties
High solids tolerance (sometimes) Corrosive
Reduces or prevents hole enlargements in salt zones
Difficult to maintain pH
May offer superior penetration rate due to low solids content at modest density
May interfere with open-hole logs
May be more dense than needed
26 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Most salt muds are sodium Most salt muds are sodium chloride, potassium chloride or chloride, potassium chloride or calcium chloridecalcium chlorideBentonite will not yield or Bentonite will not yield or hydrate very well in salt waterhydrate very well in salt waterIf bentonite is used, it is If bentonite is used, it is premixed in fresh water to a high premixed in fresh water to a high viscosity and then bled into the viscosity and then bled into the salt water systemsalt water system
27 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Oil based muds can be formulated to Oil based muds can be formulated to weigh as little as 7.5 ppg (900 kg/mweigh as little as 7.5 ppg (900 kg/m33) ) with mostly oilwith mostly oil
Oil based muds are used to drillOil based muds are used to drillHighly reactive shale and evaporite
formationsExtended reach drilling for low friction
coefficientDeep, high pressure, high temperature H2S
wells
28 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Oil base muds are much more Oil base muds are much more expensive per barrelexpensive per barrelEconomics are a function of Economics are a function of preventing hole problems, preventing hole problems, overall, it must save time on the overall, it must save time on the rig to be cost effectiverig to be cost effectiveOil base muds are highly toxic Oil base muds are highly toxic and disposal costs must be and disposal costs must be considered in the economicsconsidered in the economics
29 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Initially, crude oil was used but Initially, crude oil was used but was later replaced by dieselwas later replaced by dieselLow-toxicity mineral oils can be Low-toxicity mineral oils can be usedusedOil/water ratios can range from Oil/water ratios can range from 100:0 to 40:60100:0 to 40:60Low water ratios (60:40 to 40:60) Low water ratios (60:40 to 40:60) can have very high viscosities can have very high viscosities but they help minimize oil but they help minimize oil retained on cuttingsretained on cuttings
30 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Oil based muds are termed invert Oil based muds are termed invert emulsion because the water emulsion because the water phase is emulsified in the oil phase is emulsified in the oil which means that oil is the which means that oil is the continuous phasecontinuous phaseThe emulsified water droplets The emulsified water droplets contribute to viscosity which contribute to viscosity which helps suspend weight material helps suspend weight material and reduce fluid lossand reduce fluid loss
31 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
High salinity levels in the water High salinity levels in the water phase improve wellbore stability phase improve wellbore stability by creating osmotic pressures by creating osmotic pressures that dehydrate and harden that dehydrate and harden reactive shalesreactive shalesUsually try to balance the activity Usually try to balance the activity so that the water does not move so that the water does not move from the mud to the formation or from the mud to the formation or from the formation to the mudfrom the formation to the mud
32 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Components of an oil based mudComponents of an oil based mudOilBrine (usually calcium chloride)Primary and supplementary
emulsifiers (fatty acids are one)Oil-wetting agentOil dispersible bentoniteFiltration control additivesSlaked lime
33 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Toxicity is the most serious Toxicity is the most serious drawback to oil based mudsdrawback to oil based muds
The characteristics that result in The characteristics that result in superior performance of oil superior performance of oil based muds can also based muds can also contaminate the environmentcontaminate the environment
34 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
A wide variety of refined mineral A wide variety of refined mineral oils have been developed for use oils have been developed for use in low-toxicity oil based mudsin low-toxicity oil based muds
However, mineral oils are still However, mineral oils are still considered toxicconsidered toxic
35 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Synthetic based muds (SBM’s) Synthetic based muds (SBM’s) are an attempt to provide the are an attempt to provide the performance of oil based muds performance of oil based muds without the toxicity and without the toxicity and environmental problemsenvironmental problems
Unit cost per barrel is higher Unit cost per barrel is higher than oil based mudsthan oil based muds
36 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Synthetics are highly refine oil or Synthetics are highly refine oil or man made, hydrocarbon liquidsman made, hydrocarbon liquids
The continuous phase of an SBM The continuous phase of an SBM can be as much as 99% synthetic can be as much as 99% synthetic materialmaterial
First generation synthetics were First generation synthetics were esters, ethers, polyalphaolefins esters, ethers, polyalphaolefins (PAO’s), and acetals(PAO’s), and acetals
37 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Second generation SBM’s are Second generation SBM’s are isomerised olefins (IO’s), linear isomerised olefins (IO’s), linear alphaolefins (LAO’s), linear alphaolefins (LAO’s), linear alkylbenzenes (LAB’s) and alkylbenzenes (LAB’s) and paraffinparaffin
Second generation SBM’s are Second generation SBM’s are characterized by lower costs and characterized by lower costs and lower kinematic viscosities but lower kinematic viscosities but slightly higher toxicity levelsslightly higher toxicity levels
38 © 2006 PetroSkills LLC, All Rights Reserved
Solid PhaseSolid Phase
The solid phase of a drilling fluid The solid phase of a drilling fluid consists of clays, drill solids, consists of clays, drill solids, barite and LCMbarite and LCM
There are many different types of There are many different types of clays in the world but only three clays in the world but only three major groups are used in drilling major groups are used in drilling fluidsfluids
39 © 2006 PetroSkills LLC, All Rights Reserved
Solid PhaseSolid Phase
ClaysClaysBentonite (gel)Attapulgite (salt
gel)Sepiolite (high
temperature)
40 © 2006 PetroSkills LLC, All Rights Reserved
Solid PhaseSolid Phase
Bentonite particles are usually stacked plates like the pages of a book
The space between the plates for non-hydrated bentonite is less than 10 angstroms
When fully hydrated, the space between plates can be in excess of 40 angstroms
42 © 2006 PetroSkills LLC, All Rights Reserved
Solid PhaseSolid Phase
The chemical binding of water between plates and solid to solid friction increase the viscosity of water
Bentonite has good filter cake properties and can reduce fluid loss to 10 to 18 cc’s
43 © 2006 PetroSkills LLC, All Rights Reserved
Solid PhaseSolid Phase
AttapulgiteAttapulgiteDoes not yield or
absorb water like bentonite
Viscosity comes from interference between particles
Has poor filter cake qualities
44 © 2006 PetroSkills LLC, All Rights Reserved
Solid PhaseSolid Phase
Sepiolite is similar to attipulgiteSepiolite is similar to attipulgiteIt is used mostly in high temperature
wells such as geothermal wells
45 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Common drilling fluid propertiesCommon drilling fluid propertiesViscosity DensityGel strengthWater lossChemical content (chlorides, calcium,
pH, etc.)
46 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Rheology measurementsRheology measurementsViscosity
Funnel viscosity PV & YP n & k
Gel Strengths
47 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Viscosity is the proportionality Viscosity is the proportionality constant between the shear constant between the shear stress and shear ratestress and shear rate
Simply stated, it is the slope of Simply stated, it is the slope of the line on a shear stress – shear the line on a shear stress – shear rate diagramrate diagram
dv
dr
48 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Viscosity is a laminar flow Viscosity is a laminar flow concept and has little effect on concept and has little effect on turbulent flowturbulent flowNewtonian fluidNon-Newtonian fluid
49 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Newtonian fluidsNewtonian fluidsViscosity is
constant with shear rate (pump rate or velocity)
Water, gasoline, glycerin
50 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Non-Newtonian Non-Newtonian fluidsfluidsViscosity changes
with shear rate (pump rate)
Drilling mud
51 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Mathematical Mathematical models used to models used to describe muddescribe mudBingham Plastic
PV and YP The YP is the
shear stress required to initiate flow
Power-law n and k
YPPV
52 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Power-law modelCurved line on
Cartesian paperStraight line on
log-log paperUsed when
making any meaningful calculations with drilling mud
53 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Viscosity Viscosity measurementmeasurementMarsh funnelThe funnel
viscosity of water is 26 sec per quart or 28 sec per 1000 cc’s
54 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Funnel viscosity has nothing to do with shear stress versus shear rate
It cannot be used for any type of calculation
The roughneck uses funnel viscosity to determine which additives need to be mixed in the mud
55 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
ViscometerViscometerShear stress is
measured at a shear rate
PV = 600 rpm –300 rpm
YP = 300 rpm - PV
56 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
The shear rate is related to the viscometer speed by the following equation
Two speed viscometers run at 600 and 300 rpm to measure PV and YP
Multi-speed viscometers can provide viscosity data at additional shear rates
dv
drW1 7.
57 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Plastic viscosity and yield point from the viscometer
300600 PV PVYp 300
58 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
n and k from a viscometer
Where θ2 is the viscometer reading at twice the viscometer speed as θ1
θi is the viscometer reading at the shear rate
1
2log32.3
n n
i
i
drdv
k
idr
dv
59 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
To get the n and k from a viscometer, we usually use the 600 and 300 rpm reading
For n
or
1
2log32.3
n
300
600log32.3
n
60 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
For k you need the shear rate for the viscometer reading
We usually use the 300 rpm reading
nk
511300
ii
Wdr
dv 703.1
1-
300
sec 511300703.1 dr
dv
61 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
PV is an indication of the total and size of the solids in the mud
Increasing solids percent and smaller solids gives higher PV
The lower the PV the better
62 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
YPYP is an indication of the is an indication of the viscosity of the mudviscosity of the mud
High High YPYP’s compared to ’s compared to PVPV indicates high viscosityindicates high viscosity
The The YPYP is a measure of the is a measure of the interaction of the solids in the interaction of the solids in the mudmud
63 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
The viscosity at a specific shear The viscosity at a specific shear rate (pump rate) can be rate (pump rate) can be calculated using the power law calculated using the power law modelmodel
English UnitsEnglish Units
SI UnitsSI Unitsv
DDk
n
n
DD
v ph
n
phe
)(200
3
124.2
v
DDk
n
n
DD
v ph
n
phe
)(5
3
12200
64 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Drilling fluids are shear thinning, Drilling fluids are shear thinning, which means the faster you which means the faster you pump it the thinner it getspump it the thinner it gets
65 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
For annular flow, the annular For annular flow, the annular velocity can be calculated with velocity can be calculated with the following equationthe following equation
English UnitsEnglish Units
SI UnitsSI Units22
610273.1
ph DD
Qv
22
5.24
ph DD
Qv
66 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Some fluids Some fluids match the power match the power law model very law model very wellwell
Figure 4-13 – Figure 4-13 – Sea water, gel Sea water, gel and polymer and polymer mud mud
67 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Some fluids do not Some fluids do not match the power match the power law modellaw model
It may be It may be necessary to necessary to measure shear measure shear rates with a multi-rates with a multi-speed viscometerspeed viscometer
Figure 4-18 – Figure 4-18 – Flocculated Flocculated bentonitebentonite
68 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
EQUIVALENT THICKNESS, EQUIVALENT THICKNESS, μμee RHEOLOGY CONSTANTSRHEOLOGY CONSTANTS
FIGURENUMBER
DENSITY(ppg)
FUNNELVIS
(sec/qt) BPPL
(600,300)PL
(100,50) DSS (rpm) PV Yp
n(600,300) kk
n(100,50) kk
4-12 8.8 44 494 295 304 94 95 5 34 0.17 13.0 0.13 16.0
4-13 10.0 50 149 90 5 66 108 16 25 0.48 2.1 0.48 2.1
4-14 13.6 53 403 125 175 126 31 15 18 0.54 1.1 0.37 28.0
4-15 10.6 160 1288 174 174 108 43 21 114 0.74 1.3 0.74 1.3
4-16 15.0 62 82 46 102 70 81 29 7 0.85 0.2 0.43 2.45
4-17 9.0 43 226 66 66 62 25 8 10 0.54 0.6 0.54 0.6
4-18 9.0 48 1578 584 893 203 18 3 15 0.22 4.6 0.09 9.4
69 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Temperature will also influence Temperature will also influence the viscosity downholethe viscosity downhole
The viscosity at the surface may The viscosity at the surface may not be the same as the viscosity not be the same as the viscosity in the annulus at elevated in the annulus at elevated temperaturestemperatures
70 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
The viscosity of The viscosity of bentonite and bentonite and water can water can change with change with temperaturetemperature
71 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Increasing viscosityIncreasing viscosityAdd bentoniteDrill solids will add viscosity but drill
solid concentration should be minimized
Adding barite will thicken the mud due to an increase in solids content
In heavy muds, the bentonite content should be limited
72 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Bentonite can be flocculated in order to increase viscosity by adding lime (Ca(OH)2)
Often called spud mudsPolymers can also be used to
increase the viscosity of drilling fluids
73 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Polymers are added to water Polymers are added to water based muds to change viscosity based muds to change viscosity and other propertiesand other properties
Some polymers are:Some polymers are:SPAPolyacrylamides (PHPA)X-C Polymer
74 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Sodium polyacrylate (SPA)Sodium polyacrylate (SPA)High molecular weight, long chain
acts as a bentonite extenderMedium molecular weights are used
to control fluid lossLow molecular weights are used as
deflocculants
75 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
Polyacrylamides (PHPA)Polyacrylamides (PHPA)Very long chain polymerAdds viscosityHelps to inhibit shaleStabilizes shale cuttings
76 © 2006 PetroSkills LLC, All Rights Reserved
Types of Drilling FluidsTypes of Drilling Fluids
XC polymersXC polymersVery long chain polymerAdds viscosity especially at low shear
ratesDegrades above 250°F (120°C)
77 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Viscosity reductionViscosity reductionAdd water in unweighted mudMechanical solids controlChemical thinners reduce viscosity by
limiting the interaction of solids in the mud
Many chemical thinners are dispersants because they disperse the clays
78 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Phosphates are the oldest thinners but are limited to about 175o F (80o C)
Lignosulfonates Byproduct of the lumber industry Decompose above 200o F (90o C) When complexed with heavy metals
they are stable to 300o F (150o C) (toxic) Insoluble at pH less than 9.5 Does not disperse clays but well keep
them separated if introduced after the lignosulfonate is in the mud
79 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Lignite Sub-bituminous coal Reduces gel strengths Good to 250o F (120o C) When complexed with heavy metals it is
good to 350o F (175o C) (toxic) Not very soluble
80 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Tannins Made from the bark of the Quebracho
tree Used in high pH lime muds Good to 200o F (95o C) Complexed with chrome for stability to
400o F (200o C) – toxic
Today – high temperature thinners are special polymers and are more expensive
81 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
ContaminantsContaminantsCement contamination
Show high pH and high viscosity Best to throw it away Pretreat with bicarbonate (NaHCO3)
Carbonate contamination The drilling fluid will flocculate Lime will precipitate the carbonates
82 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
CO2 contamination Lowers the pH Mud will be very thick Raise the pH with caustic Add lime Raise the mud weight to prevent influx of
carbon dioxide Lime muds are resistant to CO2
contamination by maintaining excess lime in the mud
83 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Muds that exhibit erratic Muds that exhibit erratic behavior and are expensive to behavior and are expensive to maintain should be discardedmaintain should be discarded
It will be cheaper to build new It will be cheaper to build new mud rather than chemically treat mud rather than chemically treat an old mudan old mud
84 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Gel strengthGel strengthMeasured at 10 seconds and 10
minutes with the viscometerMud is stirred at high speed for 10
seconds and then stoppedThe gel strength is the maximum dial
reading when starting the rheometer after stopped for 10 seconds and repeated for 10 minutes
85 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Gel strengthGel strengthIndication of how well the drilling fluid
will suspend cuttings and bariteMay cause problems with lost
circulation if too high
86 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
DensityDensityThe density of the drilling fluid is
measured with a mud balanceDensity can be increased by adding
solids or saltsCommon solids
Gel Drill solids Barite
87 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Fluid loss or Fluid loss or water losswater loss
Measured in a Measured in a filter press with filter press with a pressure a pressure differential of differential of 100 psi100 psi
88 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Fluid loss is measured in cc’s Fluid loss is measured in cc’s per 30 minutesper 30 minutes
Can also measure high Can also measure high temperature, high pressure fluid temperature, high pressure fluid loss (HTHP), which is 500 psi loss (HTHP), which is 500 psi (3,447 KPa) pressure differential (3,447 KPa) pressure differential at a selected temperatureat a selected temperature
89 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
Why reduce the fluid lossWhy reduce the fluid lossTo minimize formation damageThin the filter cakeReduce differential pressure stickingReduce shale sloughing?
90 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
The fluid loss is measured through a The fluid loss is measured through a piece of filter paper with a piece of filter paper with a permeability of 30 to 40 mdpermeability of 30 to 40 mdFluid loss can be reduce by having a Fluid loss can be reduce by having a dispersed bentonitedispersed bentonitePolymers thicken the fluid phase and Polymers thicken the fluid phase and reduce fluid lossreduce fluid lossSome polymers attach themselves to Some polymers attach themselves to the clay particles to help reduce fluid the clay particles to help reduce fluid losslossSome polymers, such as starch, can Some polymers, such as starch, can actually form a filter cakeactually form a filter cake
91 © 2006 PetroSkills LLC, All Rights Reserved
Drilling Fluid PropertiesDrilling Fluid Properties
There is a There is a difference difference between static between static and dynamic and dynamic filtrationfiltration
Device to Device to measure measure dynamic fluid dynamic fluid loss through loss through corescores
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Drilling Fluid PropertiesDrilling Fluid Properties
Depending upon Depending upon the additive, the the additive, the dynamic fluid dynamic fluid loss can actually loss can actually increase when increase when static fluid loss static fluid loss decreases below decreases below a certain pointa certain point
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Drilling Fluid PropertiesDrilling Fluid Properties
The concept The concept of reducing of reducing fluid loss to fluid loss to reduce shale reduce shale sloughing is sloughing is controversialcontroversial
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Drilling Fluid PropertiesDrilling Fluid Properties
The permeability of shale is very low and generally in the range of 0.001 md or less
The permeability of the filter cake is higher than the shale
Shales do absorb water but it is not due to filtration
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Drilling Fluid PropertiesDrilling Fluid Properties
Fluid up-take may be due to any number of effects such as imbibition, capillary pressure, osmosis, etc.
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Specialized FluidsSpecialized Fluids
The search for special purpose The search for special purpose mud systems began almost mud systems began almost simultaneously with the simultaneously with the introduction of rotary drilling to introduction of rotary drilling to the petroleum industrythe petroleum industry
No one mud system will work No one mud system will work everywhereeverywhere
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Specialized FluidsSpecialized Fluids
Calcium Treated Muds - Lime Calcium Treated Muds - Lime Treated MudsTreated MudsLime muds were introduced in the
1930’sThey are characterized by high pH
(pH=12+) water base fluids containing dispersant concentrations of 6 to 20 pounds/barrel and excess lime Ca(OH)2 concentrations of 2 to 8 pounds/barrel
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Specialized FluidsSpecialized Fluids
Theoretically, the Ca++ ion helps to inhibit the mud
Gyp muds or muds treated with gypsum (CaSO4) where introduced because it has higher concentrations of the calcium ion
Calcium Chloride muds were introduced in the 1950’s
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Specialized FluidsSpecialized Fluids
Regardless of all the attention given the calcium treated muds at the time of their introduction, such systems are not frequently used today
Lime muds are used where CO2 contamination is a problem
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Specialized FluidsSpecialized Fluids
Potassium MudsPotassium MudsThe beneficial effects of K+ in the
prevention or reduction of the hydration of montmorillonite has been known to the industry for many years
In some areas, potassium muds work fairly well to inhibit shales
Shales still hydrate, the presence of potassium slows it down
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Specialized FluidsSpecialized Fluids
Additionally, the activity of the KCl mud must be balanced with the formation as in oil muds
Phosphate MudsPhosphate MudsMud systems containing large
concentrations of the common additives TSP (Tri-sodium phosphate), SMP (Sodium Metaphosphate), SAPP (Sodium acid pyrophosphate) and STP (Sodium tetraphosphate) have been used with some success
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Specialized FluidsSpecialized Fluids
The phosphate muds are usually used at low temperature when calcium contamination is a problem
Magnesium MudsMagnesium MudsSystems comprised of bentonite treated
with magnesium oxide (MgO) have enjoyed some following.
"MAG-OX" or "MAGOO" muds offered inexpensive thickness and the inhibited qualities of Mg++ simultaneously
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Specialized FluidsSpecialized Fluids
Because of the high fluid loss, they are not used very often
The "perfect" mud system does The "perfect" mud system does not exist but the search not exist but the search continuescontinues
No system can reasonably be No system can reasonably be expected to be more than expected to be more than adequateadequate
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Specialized FluidsSpecialized Fluids
Remember, the mud must be Remember, the mud must be cost effectivecost effective
If more is spent on the mud, the If more is spent on the mud, the total cost of the well must be total cost of the well must be reducedreduced