8/11/2019 AADE-06-DF-HO-36

1/7

AADE-06-DF-HO-36

Salt vs. Non-Salt Cement SlurriesA Holistic ReviewJames Heathman and Richard Vargo, Halliburton

Co!right "##$, AA%& %rilling 'luids (echnical Con)erence

(his aer was reared )or resentation at the AA%& "##$ 'luids Con)erence held at the *!ndham +reensoint Hotel in Houston, (eas, Aril -", "##$. (his con)erence was sonsored b! the

Houston Chater o) the American Association o) %rilling &ngineers. (he i n)ormation resented in this aer does not re)lect an! osition, claim or endorsement made or imlied b! the AmericanAssociation o) %rilling &ngineers, their o))icers or members. uestions concerning the content o) this aer should be directed to the individuals listed as author/s o) this wor0.

Abstract

(he toic o) when to use salted vs. non-saltedcement slurries has been around )or decades and still

arises )re1uentl!. (he answers var! deending on thesituation and the bac0ground o) the erson being as0ed.(his mied bag o)ten contributes more con)usion than

clari)ication because well lanners o)ten see0 a universalanswer that does not eist. (he correct answer to thissimle 1uestion is 2it all deends.3 (he variables

involved in ma0ing the correct decision are mostl!covered in eisting literature, but there is lac0ing an all-

inclusive treatment on the sub4ect.(he t!e o) 1uestions that should be raised an! time

this toic arises should at least consider 56 the)ormation t!es 5halite, anh!drite, reactive shales,

mineralog! o) salt )ormations other than halite, etc.6 thatthe cementing )luids will contact, 5"6 comosition o) themud s!stem, 576 the wellbore temerature ro)ile, 586 theintended urose o) the casing string, and ultimatel! 596

what the set cement is to accomlish. :nl! a)ter allthese issues have been eamined can the engineerdesign a cement s!stem seci)ic to the alication

without over or under-designing. (his aer will rovidea comlete review o) salt-cementing alicationsituations, and a ractical guide to hel the well designerdecide when the use o) salt-containing cementing )luidsis aroriate, and when it is not necessar!. Also

included will be highlights o) some more recent )indings.

Background

(his aer will al! the term 2salt3 when discussing

the general toic o) cementing across redominantl!evaorate subterranean )ormations, but will al! thearoriate seci)ic mineralog! or chemistr! whenneeded. (he literature is )illed with ublications on the

toic o) salts in cements and cementing across salt

)ormations.-;S +ul) o)

8/11/2019 AADE-06-DF-HO-36

2/7

slurr! and these )ormations.

(he Fechstein grou o) evaorites that etends

across much o) northern &uroe and the North Sea is

notorious )or drilling roblems and casing collases.

%eending on where the well is located, this salt

se1uence ma! be comosed o) an! combination o)anh!drite, g!sum, bischo)ite, carnalite, halite, 0ieserite,

ol!halites, and s!lvite. !able "reroduced )rom

8/11/2019 AADE-06-DF-HO-36

3/7

indicates that, )or this articular shale, there is a limit tothe e))ectiveness o) Cl as measured b! swelling.(here)ore, the design engineer should consider both the

intent o) the cement sheath and the eosure timebetween initial contact b! the sacer and/or cementslurr! and the cement h!dration 5initial set6 when )iltratewould be less available to interact with the shale.

Collectivel!, all this data illustrates that the e))ects o) thewater activit! o) cementing )luids on reactive shales

should be a consideration in 4ob design, eseciall! when

targeting a success)ul shoe test as the rimar! goal o)cementing oeration.

(hese authors roose that, even with the lowerreactive cla! levels, leaving a )reshwater-based cementslurr! 5or sacer6 across them can result in some degree

o) destabili=ation 5so)tening6 o) these )ormations.*hether or not this so)tening is detrimental to long-term=onal isolation or casing suort )or a seci)ic well is uto the ractitioner to determine.

(he ion echange over time between )ormationsolutions and the remaining cement )iltrate 5water that isnot reacted in the CSH gel structure o) the cement6 is aver! elusive toic. (his is not a simle issue and is

a))ected b! numerous environmental variables? insituressure, temerature, ion echange e))icienc! throughthe shale membrane, cement e))ective ermeabilit!, ionconcentrations, di))erentials between )ormation and

cement )iltrate on all these, etc. (he most recentublication on this toic attemts to address all theseissues in as comlete a manner as ossible, but bear inmind that the authorsK emhasis was on cementing

across salt )ormations. Nevertheless, the 0e!recommendation reorted was to run aroimatel! 8G

NaCl 5bwow6 when cementing across massive salt5resumabl! halite6 )ormationsL an!thing else was

unnecessar!.

Salt Formation Dissolution

Several authors have reorted studies on salt

)ormation dissolution rates.#-,$-*hile not alwa!s in

agreement as to the magnitude o) dissolution, thegeneral trend o) gradual borehole enlargement as a)unction o) eosure volume and original cement )iltratesalinit! is consistent. (he di))erences between theseresearch e))orts are li0el! buried in variables such as)low regime, volumetric e))ective )low arameters, totaldissolved solids 5as oosed to siml! the salinit!6, andminute di))erences in the h!sical structure o) the saltcores 5both man-made and natural6 themselves.

Su))ice to sa!, )ormation salt dissolution does occur

to some degree but the imlications and ris0s associated

with a seci)ic 4ob must be considered on a case-b!-

case basis. 'or eamle, the evaorites o) the Fechsteingrou are most o)ten magnesium-based.

8/11/2019 AADE-06-DF-HO-36

4/7

considerabl! longer *:C time than is normall!considered )or comressive strength develoment )or anon-salt cement be)ore drilling out, 5"6 er)orming salt

)ormation contamination testing as art o) the cement labtesting rogram, or 576 redesigning the cement slurr! to

better align with the desires to minimi=e *:C time.!able 6rovides a set o) eamle data to illustrate

the variance in comressive strength develoment thatcan occur )or the same basic design b! siml! var!ingthe source o) cement and amounts o) various salts.

Comaring comressive strength rate develoment datao) various s!stems in simle table )orm can becumbersome, so the derivative 5rate o) develoment6 isalso rovided. (his method shows 1uite clearl! that

between "8 and " hours, the di))erences in rate o)

strength develoment )or all )ive slurries shown are

small.n addition to di))erences between the lab and

downhole comressive strength rami)ications, slurr!

densit! and rheolog!, thus &C%, are also a))ected. 'oreamle, Fig) +rovides a curve o) slurr! densit! withincreasing NaCl in solution, holding the water content o)the slurr! constant. Assuming a cement slurr! has

su))icient contact time across a thic0 halite )ormation toaroach saturation, this curve illustrates the e))ect ondensit! alone. (his is an ideal scenario that does notaccount )or variances in solution rate caused b! thermal

e))ects and )low atterns in an eccentric, noncircularannulus. However, the ensuing e))ects and ossiblecomounding e))ects o) the increased densit! and

rheological e))ects on &C% should be aarent to the

reader.

Salt E%%ects on Cement 1ecanical 2roerties

Several things occur simultaneousl! when salts and

Dortland cements interact, whether the salt source is)ormation-rovided or included as art o) the design.Easicall!, three distinct rocesses occur, but the! areconcurrent, so one cannot be given secial

consideration at the eclusion o) the others. (heserocesses are bul0 shrin0age, ion echange e))ects, andthe h!sical e))ects on both )ormations and the cementitsel).

S +ul) o)

8/11/2019 AADE-06-DF-HO-36

5/7

to-li1uid ratio, constant Ackno/ledgmentsdensit! was used siml! due to common convention.

(o )urther illustrate the e))ects o) borehole geometr!and stando)) and wh! each situation must be studied

individuall!, Figs) troug "0show the same casingmodeled with a larger borehole diameter and imrovedcasing centrali=ation. (he cross-section o) 'ig B showsthe cement sheath shear deterioration that was indicated

in 'ig ;. *hile this anal!sis redicts debonding and losso) cement sheath integrit! )or the )reshwater-based

cement sheath in 'igs. $ and ;, it did not redict an!signi)icant imrovement due to changes in the borehole

geometr!. However, a noticeable imrovement isredicted )or the same borehole e))ects when comaring'igs. and # o) the salt-saturated cement.

(he anal!sis in 'igs. $ through # does not account)or the salt cree that is common to the +ul) o) nder these circumstances, even though the'&A model indicated that )ailure due to debonding isli0el!, the cement sheath would still have served its

urose. Eear in mind that this articular model does notta0e into account the salt cree that occurs with man!evaorite )ormations. 'or eamle, average rates o) ".9to 7 inches er !ear are reorted in the literature )or the

>S +ul) o)

8/11/2019 AADE-06-DF-HO-36

6/7

Anh!drite 8CaS:8 #."7 #.$ ".B$#

+!sum 8CaS:8@ "H": #."8# #."" ".7"#

Eischo)ite "

8/11/2019 AADE-06-DF-HO-36

7/7

!able +7Sale S/elling !ests o% a Dee/ater Sale

'reshwater

Fluid 2ercent ,inear S/elling

35-r E;osure 6+-r E;osure

88.#8 9#.##

Cement sacer

Cement sacer with 7G Cl

Cement sacer with 9G Cl

Cement sacer with G Cl

S!nthetic drilling )luid

"$.#$

"7.BB

;.98

.7

#.

7.

"9.

B.#;

;.87

#.;

; J. H&A(H