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TABLE OF CONTENTS
Drilling Fluids
Unit Objectives...............................................................................................3
Drilling Fluids..................................................................................................3
Drilling Fluid Classification Systems...............................................................9
Drilling Fluid Additives..................................................................................1
!aterial "alance #$uations..........................................................................1%Oil&"ased Drilling Fluids...............................................................................1'
Drilling Fluid #conomics...............................................................................1(
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UNIT OBJECTIVES
)ecogni*e t+e com,onents in t+e various ty,es of drilling fluids.
#-,lain t+e advantages and disadvantages of t+e most common ty,esof drilling fluids.
rovide an e-,lanation of mud ,ro,erties as t+ey are re,orted on a/morning re,ort0.
Calculate barite and ater volumes +en c+anges are made to a ,re&e-isting mud system.
Calculate 2 and from Fann viscometer readings.
DRILLING FLUIDS
A drilling fluid is any fluid +ic+ is circulated t+roug+ a ell in order to removecuttings from a ellbore. 4+is section ill discuss fluids +ic+ +ave ater oroil as t+eir continuous ,+ase. Air5 mist and foam5 +ic+ can be used asdrilling fluids5 ill not be discussed at t+is time.
A drilling fluid must fulfill many functions in order for a ell to be drilledsuccessfully5 safely5 and economically. 4+e most im,ortant functions are6
!ud assists in ma7ing +ole by6
1. )emoval of cuttings%. Cooling and lubrication of bit and drillstring
3. oer transmission to bit no**les or turbines.
!ud assists in +ole ,reservation by
8. Su,,ort and stabili*ation of bore+ole all
. Containment of formation fluids:gas.
'. Su,,orts t+e eig+t of ,i,e and casing
;. Serves as a medium for formation logging
(. revents +ole as+ outs due to turbulence or dissolution
9. !ust be com,atible it+ drilled formations and encountered formationfluids:gas.
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Make-up ! a Drilling Fluid
and some sort of viscosifying agent. a ,ortion of t+e fluid ill be flus+ed intot+e formation. Since e-cessive filtrate can cause bore+ole ,roblems5 somesort of filtration control additive is generally added. .
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=b> Can be used alone or it+ t+inners
=c> 4+ey also reduce viscosity
=b> Used under more severe conditions t+an ,+os,+ate treatment
4+e u,,er ,ortions of most ells can use /normal0 muds
1. Care must be ta7en not to add c+emicals +ic+ may +inder t+e ma7ingof s,ecial muds later on
%. Bative clays used to ma7e t+e mud are usually ade$uate
Spe#ial Drilling Fluids
4+ese drilling fluids are made to combat ,articular abnormal +ole conditionsor to accom,lis+ s,ecific objectives. 4+ese are6
1. S,ecial Objectives
=a> Faster ,enetration rates
=b> reater ,rotection to ,roducing *ones
%. Abnormal ole Conditions
=a> ?ong salt sections
=b> ig+ formation ,ressures
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Drilling Fluid Classi!i#a$ins
. Drilling fluids are separated into three major classifications (Figure 1):
Pneumatic
Oil-Based
Water-Based
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Li"e Base Muds
1. @ater base mud
%. 4reated it+ large amounts of caustic soda5 $uebrac+o5 and lime.
Added in t+at order
3. )atio of % lb caustic soda5 1. lb $uebrac+o and lb lime ,er 1 barrelof mud
8. @ill go t+roug+ a +ig+ly viscous stage5 but ill become stable at a loviscosity
. ood ,oints
=a> Can tolerate large amounts of contaminating salts
=b> )emains fluid +en solids content gets +ig+
'. @ea7ness & it +as a tendency to solidify +en subjected to +ig+bottom&+ole tem,eratures
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Li"e-Trea$ed Muds
1. Similar to lime based mud & differ only in degree
%. A com,romise attem,t at overcoming t+e +ig+ tem,erature gelation,roblem
=a> Use less lime t+an lime&base mud
=b> Bot nearly so resistant to salt contamination
E"ulsin Muds - Oil in %a$er
1. Oil can be added to any of t+e normal or s,ecial muds it+ goodresults
%. Bo s,ecial ,ro,erties necessary
3. Batural or s,ecial emulsifying agents +old oil in tig+t sus,ension aftermi-ing
8. Oils used are6
=a> Crude oils
=b> Diesel
=c> Any oil it+ an A< gravity beteen % and
. Oil content in mud may be 1 to 8
'. Advantages are6
=a> 2ery stable ,ro,erties
=b> #asily maintained
=c> ?o filtration and t+in filter ca7e
=d> Faster ,enetration rates
=e> )educes don&+ole friction
;. !ajor objection is t+at t+e oil in t+e mud may mas7 any oil from t+e
formationsIn&i'i$ed Muds
1. !uds it+ in+ibited filtrates
%. ?arge amounts of dissolved salts added to t+e mud
3. ig+ , usually necessary for best results
8. Designed to reduce t+e amount of formation selling caused by filtrate& in+ibit clay +ydration
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. Disadvantages
=a> Beed s,eciali*ed electric logs
=b> )e$uires muc+ s,ecial attention
=c> ?o mud eig+ts cannot be maintained it+out oil
=d> ard to increase viscosity
=e> Salt destroys natural filter ca7e building ,ro,erties of clays
G(psu" Base Muds
1. A s,eciali*ed in+ibited mud
=a> Contained large amounts of calcium sulfate
=b> Add % lb:bbl gy,sum to mud system=c> Filtration controlled by organic colloids
%. Advantages
=a> !ud is stable
=b> #conomical to maintain
=c> Filtrate does not +ydrate clays
=d> ig+ gel strengt+
3. Disadvantages
=a> Fine abrasives remain in mud
=b> )etains gas in mud
Oil Based Muds
1. Oil instead of ater used as t+e dis,ersant
%. Additives must be oil soluble
3. enerally ,re&mi-ed and ta7en to t+e ellsite
8. 4o increase aniline value5 blon as,+alt and unsla7ed lime may beadded
. Advantages
=a> @ill not +ydrate clays
=b> ood lubricating ,ro,erties
=c> Bormally +ig+er drill rates
'. Disadvantages
=a> #-,ensiveE
=b> Dirty to or7 it+
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=c> )e$uires s,ecial electric logs
=d> 2iscosity varies it+ tem,erature
Inverted Emulsions
1. @ater in oil emulsion. Oil largest com,onent5 t+en ater added.
Order of addition is im,ortant
%. ave some of t+e advantages of oil mud5 but c+ea,er.
Some+at less stable
Sal$ %a$er Muds
1. Can be used eit+er com,letion
%. @eig+t can vary u, to 1 lb:gal +en saturated
3. Bo filter ca7e building ,ro,erties5 easily lost to ,orous formationsSili#a$e Muds
1. Com,osed of sodium silicate and saturated salt ater
%. as a ,ic7ling effect on s+ales +ic+ ,revents +eaving or sloug+ing
3. @ill be 1% lb:gal or +ig+er
8. Corrosive5 e-,ensive and gives ,oor electric log results
L) Slids Muds
1. ee,s amounts of clays in t+e mud at a minimum5 +ic+ ,romotesfaster and safer drilling
%. 4+ree ays to remove solids from mud
=a> ater dilution
=b> centrifuging
=c> circulate t+roug+ large surface area ,its
3. @+en clays are removed5 a minimum of viscosity controlc+emicals areneeded
8. @+en viscosity and gel strengt+ become too lo5 clay solids arere,laced by organic or sus,ended material & ,olymers
. Ot+er advantages=a> ood for drilling it+ large ,um,s and +ig+ mud volumes
=b> Alays give faster drilling
'. roblems
=a> #-cessive dilution a ,roblem
=b> Can become e-,ensive
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DRILLING FLUID CL*SSIFIC*TION S+STEMS
Nn-Dispersed S(s$e"
4+is mud system consists of s,ud muds5 /natural0 muds5 and ot+er lig+tlytreated systems. enerally used in t+e s+alloer ,ortions of a ell.
Dispersed Mud S(s$e"s
4+ese mud systems are /dis,ersed0 it+ deflocculants and filtrate reducers.Bormally used on dee,er ells or +ere ,roblems it+ viscosity occur. 4+emain dis,ersed mud is a /lignosulfonate0 system5 t+oug+ ot+er ,roducts areused. ?ignite and ot+er c+emicals are added to maintain s,ecific mud,ro,erties.
Cal#iu"-Trea$ed Mud S(s$e"s
4+is mud system uses calcium and magnesium to in+ibit t+e +ydration offormation clays:s+ales. ydrated lime5 gy,sum and calcium c+loride are t+emain com,onents of t+is ty,e of system.
,l("er Mud S(s$e"s
olymers are long&c+ained5 +ig+ molecular&eig+t com,ounds5 +ic+ areused to increase t+e viscosity5 flocculate clays5 reduce filtrate and stabili*e t+ebore+ole. "io&,olymers and cross&lin7ed ,olymers5 +ic+ +ave good s+ear&t+inning ,ro,erties5 are also used.
L) Slids Mud S(s$e"4+is ty,e of mud system controls t+e solids content and ty,e. 4otal solidss+ould not be +ig+er t+an ' to 1. Clay content s+ould not be greater t+an3. Drilled solids to bentonite ratio s+ould be less t+an %61.
Sa$ura$ed Sal$ Mud S(s$e"s
A saturated salt system ill +ave a c+loride content of 1(95 ,,m.
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*ir Mis$ Fa"-Based Mud S(s$e"s
4+ese /loer t+an +ydrostatic ,ressure0 systems are of four ty,es6 1> dry air
or gas is injected into t+e bore+ole to remove cuttings and can be used untila,,reciable amounts of ater are encountered5 %> mist drilling is t+en used5+ic+ involves injecting a foaming agent into t+e air stream5 3> foam drilling isused +en large amounts of ater is encountered5 +ic+ uses c+emicaldetergents and ,olymers to form t+e foam5 and 8> aerated fluids is a mudsystem injected it+ air to reduce t+e +ydrostatic ,ressure.
%rk.er Mud S(s$e"s
Also called com,letion fluids5 t+ese are s,eciali*ed systems designed to 1>minimi*e formation damage5 %> be com,atible it+ acidi*ing and fracturingfluids5 and 3> reduce clay:s+ale +ydration. 4+ey are usually +ig+ly treated
brines and blended salt fluids.
DRILLING FLUID *DDITIVES
!any substances5 bot+ reactive and inert5 are added to drilling fluids to,erform s,eciali*ed functions. 4+e most common functions are6
*lkalini$( and p/ Cn$rl
Designed to control t+e degree of acidity or al7alinity of t+e drilling fluid.
!ost common are lime5 caustic soda and bicarbonate of soda.
Ba#$eri#ides
Used to reduce t+e bacteria count. araformalde+yde5 caustic soda5 lime andstarc+ ,reservatives are t+e most common.
Cal#iu" Redu#ers
4+ese are used to ,revent5 reduce and overcome t+e contamination effects ofcalcium sulfates =an+ydrite and gy,sum>. 4+e most common are caustic soda5soda as+5 bicarbonate of soda and certain ,oly,+os,+ates.
Crrsin In&i'i$rs
Used to control t+e effects of o-ygen and +ydrogen sulfide corrosion.
ydrated lime and amine salts are often added to c+ec7 t+is ty,e of corrosion.Oil&based muds +ave e-cellent corrosion in+ibition ,ro,erties.
De!a"ers
4+ese are used to reduce t+e foaming action in salt and saturated saltatermud systems5 by reducing t+e surface tension.
Drilling Fluids 1%
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E"ulsi!iers
Added to a mud system to create a +omogeneous mi-ture of to li$uids =oil
and ater>. 4+e most common are modified lignosulfonates5 fatty acids andamine derivatives.
Fil$ra$e Redu#ers
4+ese are used to reduce t+e amount of ater lost to t+e formations. 4+emost common are bentonite clays5 C!C =sodium carbo-ymet+ylcellulose> and,re&gelatini*ed starc+.
Fl##ulan$s
4+ese are used to cause t+e colloidal ,articles in sus,ension to form intobunc+es5 causing solids to settle out. 4+e most common are salt5 +ydrated
lime5 gy,sum and sodium tetra,+os,+ates.
Fa"ing *gen$s
4+ey are most commonly used in air drilling o,erations. 4+ey act as surface&ants5 to foam in t+e ,resence of ater.
Ls$ Cir#ula$in Ma$erials
4+ese inert solids are used to ,lug large o,enings in t+e formations5 to,revent t+e loss of +ole drilling fluid. But ,lug =nut s+ells>5 and mica fla7esare commonly used.
Lu'ri#an$s4+ese are used to reduce tor$ue at t+e bit by reducing t+e coefficient offriction. Certain oils and soa,s are commonly used.
,ipe-Freeing *gen$s
Used as s,otting fluids in areas of stuc7 ,i,e to reduce friction5 increaselubricity and in+ibit formation +ydration. Commonly used are oils5 detergents5surfactants and soa,s.
S&ale-Cn$rl In&i'i$rs
4+ese are used to control t+e +ydration5 caving and disintegration of clay:s+ale formations. Commonly used are gy,sum5 sodium silicate and calciumlignosulfonates.
Sur!a#$an$s
4+ese are used to reduce t+e interfacial tension beteen contacting surfaces=oil:ater5 ater:solids5 ater:air5 etc.>.
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%eig&$ing *gen$s
4+ey are used to ,rovide a eig+ted fluid +ig+er t+an t+e fluids s,ecific
gravity.!aterials are barite5 +ematite5 calcium carbonate and galena.
M*TERI*L B*L*NCE E0U*TIONS
!aterial balance e$uations are used for calculating volumes and densities+en to or more insoluble materials are mi-ed toget+er.
4+e !aterial "alance #$uation is6
21@1 G 2%@% ..... H 2F@F IIIIIIIIIIIIIIIIIIIII.I=1>
+ere6 21 G 2% ..... H 2F IIIIIIIIIIIIIIIIIIIII..I=%>
+ere6 21 H 2olume of first material to be mi-ed toget+er@1 H Density of first material
2% H 2olume of second material to be mi-ed toget+er
@% H Density of second material
2F H 4otal or sum of all volumes mi-ed toget+er
@F H Density of total mi-ture. ro,ortional average of all volumesmi-ed toget+er
4+e most commonly used variables in material balance e$uations are6
Bari$e1. @eig+t of a barrel of barite ="aSO8> s.g. H 8.% g:cc
8% gal:bbl - (.33 lb:gal - 8.% H 18; lb:bbl
J since barite comes in 1 lb sac7s5 one barrel contains 18.; sac7s
%. @eig+t of a gallon of barite
(.33 lb:gal - 8.% H 38.9 lb:gal
/e"a$i$e
1. @eig+t of a barrel of +ematite =Fe%O3> s.g. H . g:cc
8% gal:bbl - (.33 lb:gal - . H 1;89 lb:bbl%. @eig+t of a gallon of +ematite
(.33 lb:gal - . H 81.' lb:gal
Lig&$ Oil
1. #-am,le & =81K A< ravity> s.g. H .(% g:cc
%. @eig+t of a gallon of oil
(.33 lb:gal - .(% H '.( lb:gal
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E1a"ple ,r'le" 23
Calculate +o many sac7s of barite are re$uired to increase t+e density of an
( barrel mud system from 1%.; lb:gal to 18. lb:gal.Slu$in 23
Using6 21@1 G 2%@% H 2F@F
+ere6 21 H ( bbls
@1 H 1%.; lb:gal
2% H un7non volume of barite
@% H 38.9 lb:gal =density of barite>
2F H 21 G 2% =or ( G 2% >
@F H 18. lb:gal
t+erefore6 (=1%.;> G 2%=38.9> H =( G 2%> - 18.
151' G 38.92% H 115' G 18.2%
%.82% H 188
2% H ;.' bbls of barite
;.' bbls - 18.; s7:bbl H 13( sac7s of barite
E1a"ple ,r'le" 46
Calculate +o muc+ ater and barite are re$uired to ma7e ( barrels of a1. lb:gal ater&based drilling mud.
Slu$in
Using6 21@1 G 2%@% H 2F@F
+ere6 21 H un7non volume of ater
@1 H (.33 lb:gal
2% H un7non volume of barite or =( & 21>
@% H 38.9 lb:gal
2F H ( bbls
@F H 1. lb:gal
4+erefore6 21=(.33> G =( & 21>38.9 H (=1.>
(.3321 G %;9% & 38.921 H (8
&%'.;21 H &19%
21 H ;3 bbls of ater
2% H ( bbls & ;3 bbls H ' bbls of barite L 18.; s7:bbl or 9' sac7s
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OIL-B*SED DRILLING FLUIDS
4+ese fluids5 because of t+eir s,ecial nature of being a mi-ture of to
immiscible li$uids =oil and ater>5 re$uire s,ecial treatments and testing,rocedures.
Dispersed ,&ase34+e li$uid ,resents in t+e form of finely divided dro,lets.
Cn$inuus ,&ase34+e li$uid ,resents in t+e form of t+e matri- in +ic+ t+edro,lets are sus,ended.
4o 7ee, t+ese li$uids stabili*ed =i.e. to 7ee, t+e dis,ersed ,+ase fromcoalescing and settling out of t+e mi-ture>5 an emulsifier is added to form aninterfacial film around t+e dis,ersed ,+ase +ic+ causes t+em to re,el eac+ot+er5 so t+ey remain dis,ersed.
4+e effectiveness of an emulsifier de,ends on t+e al7alinity and electrolytes=c+loride content> of t+e ater ,+ase5 and t+e tem,erature of t+e drilling fluid.
Ele#$ri#al S$a'ili$(
4+e electrical stability =#.S.> of an oil&based drilling fluid is t+e stability of t+eemulsions of ater in oil5 or t+e amount of current re$uired to brea7 t+eemulsifier don and allo t+e saline ater to coalesce.
1. An electrical ,robe is inserted into t+e drilling fluid and t+e voltageincreased until t+e emulsion brea7s don
=c> t+e measure of emulsion brea7don is indicated by current flo
=d> relative stability is recorded as t+e amount of voltage at t+ebrea7don ,oint
%. #.S. is recorded as t+e voltage reading and tem,erature of t+e drilling fluidsam,le
=a> adding emulsifier ill raise t+e #.S. readings
=b> normal /fres+0 mud is about 3 or +ig+er
=c> during drilling5 t+e #.S. can increase to ( or +ig+er
Oil3 %a$er Ra$i
T&e Oil3 @ater )atio is defined as t+e ,ercent oil in t+e li$uid ,+ase and t+e,ercent ater in t+e li$uid ,+ase. 4+e ,ercentages can be determined from aretort analysis of t+e drilling fluid.
E1a"ple ,r'le" 5
Determine t+e oil6 ater ratio from t+e folloing retort analysis6
Oil H 8 ater H 3' solids H 1
4+e oil6 ater ratio is '68
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4o c+ange t+e oil6 ater ratio re$uires t+e additions of oil to increase t+e ratio5and ater to decrease t+e ratio. For e-am,le5 t+e oil re$uired to increase t+e
oil6 ater ratio can be calculated using6+ere6 2i H initial of ater by volume =>
2f H final of ater in li$uid ,+ase =>
2t H initial total li$uid volume =>
2m H total mud volume =bbls>
4+e ater re$uired to reduce t+e oil6 ater ratio can be calculated using6
+ere6 2io H initial of oil by volume =>
2fo H final of oil in li$uid ,+ase
*niline ,in$
Anot+er common term used +en dealing it+ oil&based drilling fluids is t+eaniline ,oint of t+at fluid. 4+e aniline ,oint is t+e tem,erature belo +ic+ anoil containing by volume aniline =C'&B%> becomes cloudy. 4+e solvent,oers for rubber are related to t+e solvent ,oer for aniline. Oils +aving ananiline ,oint above 18oF are considered acce,table to use
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DRILLING FLUID ECONOMICS
Ta'le 23 T(pi#al C"psi$in6Cs$s 7 Un )eig&$ed Drilling Fluid 8Barrels r
punds ne#essar( $ "i1 ne 'arrel9
Com,onent 2olume Unit Cost=M>
Com,onent Cost=M>
L) Cllid Oil-Based Drilling Fluid
Diesel Oil .( bbl l8%. 33.'
#mulsifier:@ettingAgent
'. 1. 9.
@ater .18 bbl & &
el . lbs 1.% '.
Calcium C+loride %. lbs .% 8.
?ime 3. lbs .1 .3
4otal Cost %.9
Fres&-%a$er Dispersed Drilling Fluid
"entonite %. lbs .; 1.;
C+rome ?ignosulfonate '. lbs . 3.?ignite 8.lbs .3 1.%
Caustic Soda 3.lbs .8 1.%
@ater 1. bbl & &
4otal Cost =1 bbl> ;.1
:Cl ,l("er Drilling Fluid
"entonite =,re&mi-ed :%O>
. lbs .; .3
C+rome ?ignosulfonate 1. lbs . .
Caustic Soda .3 lbs .8 .1%
otassium C+loride 3. lbs .% ;.
olyanionic Cellulose %. lbs 3. '.
otassium ydro-ide .3 lbs .( .%8
4otal Cost =1 bbl> 18.%1
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Ta'le 43 T(pi#al C"psi$in6Cs$s - 2;9
L) Cllid Oil-Based Drilling FluidDiesel Oil . bbl 8%. %3.1#mulsifier:@ettingAgent
(. lbs 1. 1%.
@ater .9 bbl & &el 8. lbs 1.% 8.(Calcium C+loride 1. lbs .% 3.
?ime 3. lbs .1 .3"arite . lbs .; 3.4otal Cost =1 bbl> ;(.%
Fres&-%a$er Dispersed Drilling Fluid"entonite %. lbs .; 1.8C+rome?ignosulfonate
9. lbs . 8.
?ignite '. lbs .3 1.(Caustic Soda 8. lbs .8 1.'"arite 8. lbs .; 31.
@ater 1.bbl & &4otal Cost =1 bbl> 8.(:Cl ,l("er Drilling Fluid
"entonite =,re&mi-ed: %O>
. lbs .; .3
C+rome?ignosulfonate
1. lbs . .
Caustic Soda .3 lbs .8 .1%otassium C+loride %8. lbs .% 8.(olyinosinic Cellulose 3. lbs 3. 9.!odified Starc+ . lbs 1. .
otassium ydro-ide .3 lbs .( .%8"arite 8. lbs .; %(.4otal Cost =1 bbl> 83.1
Drilling Cndi$ins
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ig+ Angle ole =N3> - - - - - - - -
2ery )eactive S+ales - - - - - - - - - - -
Stic7ing roblems - - - - - - - -
?ost Circulation - - - - - -
!ud @eig+ts=N1',,g>
- - - - - - - -
4em,eratures=N3%F>
- - - - -
as ydrates - - -
)ecommended !ud4y,e
Oil&"ased 1 1 1 1 % 1 1
?ignosulfonate 1 % 1 % %
olymer % 1 % 3 % 1 3
otassium ?ime 1 1 1 3 3 %
4o use t+is c+art6 are6
=1> oil&base5
=%> ,olymer and
=3> ,otassium lime