Cationic Organic Polymer Formation Damage ... - ACS Publications

Chapter 10

Cationic Organic Polymer Formation Damage Control Chemicals Downloaded by PENNSYLVANIA STATE UNIV on December 6, 2015 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch010

A Review of Basic Chemistry and Field Results John K. Borchardt Westhollow Research Center, Shell Development Company, Houston, T X 77251-1380 Polymers containing quaternary ammonium s a l t groups i n some or all of the polymer repeat units have been evaluated as formation damage control agents i n drilling, completion, a c i d i z i n g , and hydraulic fracturing f l u i d s as well as i n enhanced oil recovery. Important chemical structure proper t i e s determining effectiveness of formation damage control polymers include polymer molecular weight and location of the quaternary ammonium group i n the polymer repeat unit structure. S t a t i s t i c a l l y s i g n i f i c a n t sets of field results indicate two of these polymers are e f f e c t i v e formation damage control agents i n a c i d i z i n g oil and gas wells. Formation damage has become widely recognized as a major contribut ing factor to rapid productivity decline after well completion or workover. The reduction of formation damage during and after well completion and workover treatments w i l l improve long-term well productivity. The use of certain quaternary ammonium s a l t polymers to substantially reduce clay swelling and fines migration has become common practice during d r i l l i n g and well completion and stimulation operations (1). Gabriel and Inamdar found that quaternary ammonium salt polymers which were highly e f f e c t i v e s t a b i l i z e r s of water-swelling clays did not protect test cores from permeability damage caused by fines migration i n the substantial absence of water-swelling clays (2). E a r l i e r Reed and Coppel noted similar results when evaluating an e f f e c t i v e water-swelling clay s t a b i l i z e r , hydroxyaluminum, as a s i l i c a fines s t a b i l i z e r (3). S i l i c a fines were s t a b i l i z e d only when the unconsolidated test sand contained at least 2% smectite, a water-expandable clay. More recently certain quaternary ammonium s a l t polymers have been claimed to be e f f e c t i v e i n substantially reducing f i n e p a r t i cle migration even i n the absence of water-swelling clays (1). However, there i s l i t t l e information r e a d i l y available concerning 0097-6156/89/0396-0204$06.00/0 o 1989 American Chemical Society In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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the e f f e c t of chemical structure on polvmer performance. There fore, i t i s worthwhile to review the technical and patent l i t e r a ture on these polymers to determine the e f f e c t of polymer molecular weight and repeat unit structure on the performance of these organic polymers as swelling clay and mineral f i n e p a r t i c l e s t a b i lizers. Formation Damage. While the causes of formation damage are numer ous and may vary from one f i e l d to another, they may be grouped into the following general categories: 1. the migration of existing mobile fines within the formation. This i s caused by fines entrainment i n rapidly flowing f l u i d s . Later f i n e p a r t i c l e deposition i n c a p i l l a r y constrictions causes reduced permeability. 2. generation of mobile fines as a r e s u l t of a c i d i z i n g a formation. Fines may also be created by crushing of proppant grains during mixing and pumping of fracturing f l u i d gels or by the e f f e c t of overburden pressure on proppant grains after fracture generation. 3. The creation of mobile fines r e s u l t i n g from low s a l i n i t y aqueous f l u i d s contacting water-expandable clays. While clay swelling w i l l reduce c a p i l l a r y diameter thus decreasing rock permeability, the major mode of formation damage i s thought to be the generation of mobile f i n e p a r t i c l e s . This occurs when the swelling clays act as the primary cementing medium of the forma t i o n . Clay expansion increases the mobility of pre-existing f i n e p a r t i c l e s formerly cemented i n place. In addition, the expanded clay i t s e l f i s more l i k e l y to undergo disintegration and subsequent migration i n the presence of rapidly flowing f l u i d s . 4. fines contained i n completion, workover, and stimula t i o n f l u i d s may be introduced into the formation. These fines usually plug flow channels before they penetrate deeply into the formation, F i l t r a t i o n of treatment and i n j e c t i o n f l u i d s has become a widespread practice to deal with t h i s problem. Perforating also causes near-wellbore formation damage due to rock crushing and f i n e p a r t i c l e generation. Other minerals beside water-swelling clays have been found to undergo fines migration. The permeability damage caused by essen t i a l l y non-swelling clays such as k a o l i n i t e and c h l o r i t e i s a well-known phenomenon. S i l i c a fines have been i d e n t i f i e d as a potential source of permeability damage i n various poorly consoli dated U.S. Gulf Coast formations (1). Other minerals i d e n t i f i e d as constituents of mobile f i n e p a r t i c l e s include feldspar, c a l c i t e , dolomite, and s i d e r i t e (4,5). The migration of iron mineral f i n e s , primarily hematite and magnetite, i s a common occurrence i n portions of the Appalachian Basin. The phenomenon often occurs after well stimulation and can r e s u l t i n the continuing production of iron mineral fines which pose a s i g n i f i c a n t disposal problem. The migration of iron mineral fines through propped fractures can substantially reduce the fracture flow capacity. Many of these are mineral fines are native to the formation and are not formed by p r e c i p i t a t i o n of acid-solu ble iron s a l t s present i n i n j e c t i o n waters during or after a c i d i -

In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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zing. (These iron s a l t s can p r e c i p i t a t e as the acid spends and the pH increases.)


Organic Polymer Structures Some of the structures of the organic polymers claimed i n the patent l i t e r a t u r e to be e f f e c t i v e swelling clay or mineral f i n e p a r t i c l e s t a b i l i z e r s are detailed i n Table I. Chemical structure considerations f o r f i e l d use include compatibility with fracturing polymer (polysaccharide) crosslinkers and enhanced o i l recovery (EOR) chemicals such as anionic surfactants and p a r t i a l l y hydro lyzed polyacrylamides and high pH solutions used i n caustic flood ing. Structures which cause the polymer to increase agueous f l u i d v i s c o s i t y are undesirable. High temperature (500 -600 F) can also be an important consideration f o r high temperature formations or use i n thermal EOR processes such as steam i n j e c t i o n . Organic polymers claimed to be e f f e c t i v e swelling clay and mineral f i n e p a r t i c l e s t a b i l i z e r s i n the patent l i t e r a t u r e can be divided into four classes. The polymers of class 1 have the quaternary nitrogen atom as part of the polymer backbone (6-10). Polymers i n t h i s class include poly(dimethylamine-co-epichlorohydrin, abbreviated poly(DMA-co-EPl), and poly(N,N,N',N'-tetramethyl1,4-1,4-diaminobutane-co-l,4-dichlorobutane), abbreviated poly (TMDAB-co- DCB). These low molecular weights are not surprising since these are condensation polymers. Molecular weights c i t e d range from 800 to 800,000 daltons. Polymers i n which the quarternary nitrogen atom i s part of a f i v e - or six-membered ring comprise the second class of polymers. The ring forms part of the polymer backbone as indicated by the second and t h i r d polymer repeat units given i n Table I. The member of t h i s class c i t e d i n several patents i s p o l y ( d i a l l y l d i m e t h y l ammonium chloride) abbreviated poly(DMDAAC). Both f i v e - and six-membered ring structures (see Table have been proposed f o r poly(DADMAC). The most recent work, a C NMR study, supports a five-membered ring structure f o r the polymer repeat unit (10). High molecular weight products may be synthe sized by free r a d i c a l polymerization. DADMAC polymers having molecular weights as high as 2.6 X 10 daltons have been evaluated as clay s t a b i l i z a t i o n agents (12). Both poly(DMA-co-EPl) and poly(DADMAC) have been widely used in the f i e l d i n a c i d i z i n g , hydraulic fracturing, sand control, and other well treatments (12). The t h i r d class of polymers contains one or more nitrogen atoms on a pendant sidechain i n the polymer repeat unit (13,14). The nitrogen may or may not be quaternary. In addition to being swelling clay s t a b i l i z e r s , these polymers also s t a b i l i z e nonswelling mineral f i n e p a r t i c l e s . Limited molecular weight data i g available but molecular weight values from 50,000 to 1 X 10 daltons have been c i t e d for various polymers. The f i n a l class of polymers are copolymers containing one or more of the repeat units of classes 2 and 3 (15-18). Copolymer effectiveness would presumably be a function of the chemical structures of each comonomer, comonomer sequence d i s t r i b u t i o n , and polymer molecular weight. The comonomer could be a r e l a t i v e l y


10. BORCHARDT

207


Table I. Chemical Structures of Clay and Mineral Fines Stabilizers Reference

Polvmer Repeat Unit

S

OH CH

3

6-9,12,13

+

--CH CHCH N 2

2

CH

3

"CH \

^ CH


2

\i \

—

2

r

CH

2

6-10,12,13

cr

+

CH

CH

3

X /

3

cr

+ /

CH

CH

3

'

3

n

6-9

{CH-r;N+ ( C H ^ ^ ncr « CH r; N (CH)-^ CHiij N (CH -r r e CH CH N (CH^-r^ nCr 2

+

2

3

2

3

r

6-9

2nCP

+

n

6-9

+

2

2

2nBr"

+

(• N (CH ) -fCH t7 N * (CH)-fCHz-rrr; CH 3

2

2

3

2

12

3

-CH-C 2

I C=0

12, 14

CI

NHi-CHrr N (CH)-CHCHCH-N (CH), +

+

3

2

2

I

3

OH

CH,

CH-C 2

15

C=0 ci OH NH-f C H ^ N • (CH)-tCH^7 N * (CH)~CHCHCH-N (CH ) +

3

^—CH-CH2- ^

2

2

2

2

3

2

3

2

N

2

2

3

2

17

yd"

N

CH,

16

CH-C 2

i

^

CO H y

^

2

C 0 CH CH N (CH )

CH-C2

2

^CH -C(CH )—

6CH,

3

I

C0 CH CH N(CH) y 2

2

2

3

2

CH,

CH I

CH-C 2

3

CH-C

I

2

c=o

OH

I

+

NH-t CH-r- N (CH ) -CHCHCHN + (CH ) 2

3

3

2

2

2

3

3

18

cI = o I

0-KH -r;N(CH ) 2

3

2

CH

3

A = +CHC 2

C 0 H or Na 2


OIL-FIELD CHEMISTRY

208

inexpensive chemical as compared to the nitrogen-containing mono mer. Only copolymers of class 3 repeat units appear to have been studied.


Laboratory Test Procedures Swelling Clay S t a b i l i z a t i o n . The laboratory evaluation test f o r swelling clay s t a b i l i z e r s i s described i n d e t a i l i n reference (18). B r i e f l y , a test column containing a blend of 85% (by weight) 70-170 U.S. mesh sand, 10% s i l i c a f l o u r (m.

was

aqueous

5%

KC1.

Results indicated that poly(DADMAC) w i l l reduce damage caused by contact of low s a l i n i t y f l u i d l o s t from the cement s l u r r y with swelling clays present i n the formation. An increase i n poly (DADMAC) molecular weight from 600,000 to 2.6 X 10 daltons r e s u l ted i n a decreased polymer effectiveness. The test columns were of r e l a t i v e l y high permeability so the thickness of the adsorbed polymer layer, predicted to be greater for the higher molecular weight polymer, would have l i t t l e e f f e c t on the observed flow rates. Laboratory Test Results - Mineral Fines S t a b i l i z e r s While clay swelling and concomitant f i n e p a r t i c l e migration i s a major cause of permeability damage, reduction of permeability caused by fines migration i n the absence of swelling clays can also occur. This fines migration i s due to a combination of chemical and mechanical forces and i s greatest i n the near-wellbore region where f l u i d flow rates are highest. Mineral f i n e p a r t i c l e s which can cause permeability damage include s i l i c a , r e l a t i v e l y nonswelling clays such as k a o l i n i t e , carbonates such as c a l c i t e and dolomite, and iron minerals such as hematite, s i d e r i t e , and magne tite. A series of U.S. patents (13-17) indicate that polymers containing nitrogen atoms i n r e l a t i v e long sidechains are effec t i v e i n reducing the migration of the various mineral f i n e p a r t i cles enumerated above. Homopolymers. Polymers such as poly(methacrylamido-4,4,8,8-tetramethyl-4,8-diaza-6-hydroxynonamethylene dichloride), abbreviated poly(MDTHD), and a t r i a z a analog, abbreviated poly(MTHHDT), have been shown to be e f f e c t i v e s t a b i l i z e r s of s i l i c a , c a l c i t e , and hematite (14,15) as indicated by the data summarized i n Table V. Results indicated that swelling clay s t a b i l i z e r s such as poly (DMA-co-EPl) which do not possess a quaternary nitrogen atom i n a pendant chain may not be very e f f e c t i v e at preventing permeability damage due to fines migration i n the absence of water-swelling clays.


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Table V. Mineral Fines Production From Unconsolidated Test Columns

3

Mineral Fines Production (% of untreated column), mineral fines used: silica calcite hematite poly(MDTHD) (2) 5.8 28.0 39.5 poly(MTHHDT) (3) 14.3 83.3 66.7 poly(APTMAC) (2) 65.0 49.6 139.5 poly(DMA-co-EPI) (0) 65.0 165.4 139.5


Polymer (N atoms in sidechain)

a. The polymer solvent was aqueous 2% NH^Cl. Polymer concentration was 2% by weight active material. Test temperature was 62.8 C (145 F ) . Mineral fines production was measured during i n j e c t i o n of 27 pore volumes of fresh water. The methacrylamide backbone of the most e f f e c t i v e polymers suggests they are produced by free r a d i c a l copolymerization. Rela t i v e l y l i t t l e molecular weight information on these polymers i s available although the molecular weight of a t r i a z a analog of MDTHD has been given as 135,000 daltons (15). Similar polymers having acrylamide backbones such as poly(acrylamido-3-propyltrimethylammonium chloride), abbreviated poly(APTMAC) appear less e f f e c t i v e i n t h i s application (14) probably due to t h e i r greater tendency to increase aqueous f l u i d v i s c o s i t y and thus suspend s o l i d s (Table V). Copolymers. Copolymers have also been studied (16-18). While one comonomer contains 1-2 quaternary nitrogen i n a f l e x i b l e pendant chain, the other comonomer was nonionic. Copolymers of the methyl chloride s a l t of dimethylaminoethyl methacrylate (one quaternary nitrogen atom) and dimethylaminoethyl methacrylate (DMAEMA) and of MDTHD (2 quaternary nitrogen atoms) and DMAEMA, N,N-dimethylacrylamide (NNDMAm) or dimethylaminopropyl methacrylate (DMAPMA) have been studied and the results summarized i n Table VI. Copolymers of MDTHD and DMAPMA appeared to be the most effec t i v e s i l i c a , c a l c i t e , and hematite mineral fines s t a b i l i z e r s . Increasing the copolymer MDTHD content had l i t t l e e f f e c t on polymer performance. Similar results were observed f o r a series of MDTHD DMAEMA copolymers and a series of DMAEMA*CH C1 s a l t - DMAEMA copolymers (Table VI). In contrast, increasing the MDTHD content of MDTHD - NNDMAm copolymers from 67% to 90% improved copolymer performance as a s i l i c a fines and hematite fines s t a b i l i z e r . Terpolymers of DMAEMA, the methyl chloride s a l t of DMAEMA, and a termonomer: the sodium s a l t of 2-acrylamido-2-methylpropane sulfonic acid (AMPS), methacrylamidopropyltrimethylammonium chlo ride (MAPTAC), or NNDMAm, were studied (Table VI). For 9% termonomer, AMPS-containing polymers provided the most e f f e c t i v e s i l i c a fines s t a b i l i z a t i o n . This was somewhat surprising since MAPTAC contains a quaternary ammonium group on a f l e x i b l e sidechain. Consistent with the r e l a t i v e l y poor performance of the 9% MAPTAC terpolymer was the observation that, when the terpolymer MAPTAC content was increased from 9% to 33%, s i l i c a fines s t a b i l i zation was not substantially increased. 3



DMAEMA DMAEMA DMAEMA DMAEMA DMAEMA

3

CH-Cl:DMAEMA CH^Cl:DMAEMA CH^Cl:DMAEMA CH^Cl:DMAEMA CHC1 :DMAEMA

1:2 MDTHD:DMAEMA£ 1:1 MDTHD:DMAEMA

1:9 1:3 1:1 3:1 1:1

7:3 MDTHD:DMAPMA 8.75:1.25 MDTHD:DMAPMA 9.0:1.0 MDTHD:DMAPMA 9.5:0.5 MDTHD:DMAPMA

2.7 2.6 2.6 2.6 5.1

1.7 2.6

1:2 MDTHD:DMAEMA 1:1 MDTHD:DMAEMA 2:1 MDTHD:DMAEMA

1:2 2:1 2:1 9:1

1.6 1.9 2.2

Treatment F l u i d V i s c o s i t y (cps)

MDTHD:NNDMAm MDTHD:NNDMAm MDTHD:NNDMAm MDTHD:NNDMAm

Copolymer

27.6 20.7

23.8 23.8 38.1 28.6 23.8

29.4 26.5 29.4 32.4 35.3

23.5 23.5 23.5

14.3 14.3 23.8 9.5 19.1 9.5 9.5

32.4 35.3 20.6 26.4

38.1 42.3 19.1 14.3

Silica before 15% HCl injection

100.0 114.6

Continued on page 214

77.8

57.1

100.0

94.4

88.9 72.2

81.1

37.2

77.8

Mineral Fines Production (% of untreated test column) Silica Hematite Calcite after 15% HCl injection

TABLE VI. EFFECTIVENESS OF COPOLYMERS AS MINERAL FINES STABILIZERS'



Treatment F l u i d V i s c o s i t y (cps)

29.4 29.4 29.5

33.3 23.8 33.3

Data taken from reference 18.

38.2

Mineral Fines Production (% of untreated test column) Silica Calcite Hematite after 15% HCl injection

42.9

Silica before 15% HCl injection

a. See footnote a, Table V f o r experimental d e t a i l s . b. The polymer solvent was aqueous 15% HCl.

DMAEMA ( C H ) SO :DMAEMA:AMPS 45.5:45.5:9 1.9 DMAEMA (CH\J SO,:DMAEMA:NNDMAm 45.5:45.5:9 2.0 DMAEMA CH-CI:DMAEMA:MAPTAC 45.5:45.5:9 2.0 DMAEMA CH-Cl:DMAEMA:MAPTAC 33.3:33.3:33.3 1.8

Copolymer

TABLE VI (continued). EFFECTIVENESS OF COPOLYMERS AS MINERAL FINES STABILIZERS

3


3

S3 H

s

a

a

P

O

4^

10. BORCHARDT


215

The observation that the quaternary ammonium monomer content of MDTHD:DMAEMA and DMAEMA CH C1:DMAEMA copolymers had l i t t l e e ffect on t h e i r s i l i c a fines s t a b i l i z a t i o n properties of prompted an investigation of nonionic polymers as mineral fines s t a b i l i z e r s (17,18). A series of N-vinylpyrrolidinone (NVP) copolymers with DMAEMA have been studied. Results are summarized in Table VII. 3


Table VII. Reduction of Mineral Fines Production Using NVP Copolymers

NVP Comonomer % by weight comonomer

Mineral Fines Production (% of untreated test column) DMAEMA DMAEMA DMAEMA DMAEMA-DMAEMA(CH^SO^ 20

Molecular Weight lxlQ Mineral Fines Silica before 15% HCl 9.5 after 15% HCl 9.5 Silica/Kaolinite before 15% HCl after 15% HCl Calcite Hematite

20 5

lxlQ

17.6

75.6 52.9 69.8 32.4

8 6

lxlQ

9.5 20.6

12 6

8 lxlQ

6

14.3 14.4 4.4 5.3 51.2 47.6

a. See footnote a, Table V and Laboratory Test Procedures for experimental d e t a i l s .

section

Limited s i l i c a fines s t a b i l i z a t i o n data indicated that i n creasing copolymer molecular weight from 100,000 to 1,000,000 daltons had, i f anything, a negative e f f e c t on s i l i c a fines s t a b i l i z a t i o n . At a molecular weight of 1,000,000 daltons, t h i s copo lymer appeared to be more e f f e c t i v e i n s t a b i l i z i n g s i l i c a fines than s i l i c a / k a o l i n i t e , c a l c i t e , or hematite f i n e s . However, the results may be due i n part to the larger p a r t i c l e size and lower surface area of the s i l i c a fines (see Table I I ) . When the DMAEMA content of NVP - DMAEMA copolymers was reduced from 20% to 8%, the s i l i c a fines s t a b i l i z a t i o n effectiveness appeared to improve s l i g h t l y . When the 80/20 NVP - DMAEMA copo lymer was converted to a terpolymer containing 8% DMAEMA (CH^^SO^, s i l i c a fines s t a b i l i z a t i o n was substantially unaffected. However, s t a b i l i z a t i o n of s i l i c a / k a o l i n i t e fines was greatly improved. This suggested that the interaction of polymer quaternary nitrogen atoms with anionic s i t e s on mineral surfaces was important f o r the s t a b i l i z a t i o n of migrating clays but a d i f f e r e n t interaction was important f o r the s t a b i l i z a t i o n of s i l i c a f i n e s . C a l c i t e fines s t a b i l i z a t i o n improved while hematite fines s t a b i l i z a t i o n effec tiveness decreased. This also indicated the nature of the adsorbed polymer - f i n e p a r t i c l e complex varied f o r d i f f e r e n t minerals. Berea core flood test results (Table VIII) suggested that the presence of DMAEMA (CH^^SO^ improved the permeability damage c h a r a c t e r i s t i c s of 80% "NVP copolymers. The kerosene flow rate



400 800 1350 1450 2560 2960

104 246 27 --22 185

80:20 poly(NVP-co-DMAEMA) Cumulative Stabilized Volume Injected Permeability (cc) (md)

800 1200 1600 1700 2115 2515

45 239

552 243 34

80:12:8 poly(NVP-co-DMAEMA-co-DMAEMA ( C E ^ S O ^ Cumulative Stabilized Volume Injected Permeability (cc) (md)

a. See reference 17 f o r experiment d e t a i l s . T = 60°C (140°F). Polymer molecular weight was 1,000,000 daltons. The Berea sandstone test cores contained 5-10% k a o l i n i t e , 2-5% i l l i t e , 0-2% c h l o r i t e , amd 0-5% mixed layer clays. b. The polymer solvent was aqueous 2% by weight ammonium chloride solution.

Synthetic Brine Kerosene Synthetic Brine 0.25%w polymer Synthetic Brine Kerosene

Injected F l u i d

3

TABLE VIII. PERMEABILITY DAMAGE CHARACTERISTICS OF NVP COPOLYMER MINERAL FINES STABILIZERS - BEREA CORE TESTS


w S o w

O

OS

to


10. BORCHARDT


217

after polymer treatment of the core was 98% of the pretreatment flow rate when the polymer contained 8% DMAEMA (CH^^SO^ compared to 75% when no DMAEMA (CH^^SO, was present i n the polymer. The r e s u l t s summarized i n Table IX indicated that another copolymer which does not contain quaternary nitrogen atoms, poly (DMAEMA - co - methyl acrylate) was also an e f f e c t i v e s i l i c a fines stabilizer. Increasing the molecular weight of a copolymer containing 5% methyl acrylate (MA) from 100,000 to 1,000,000 daltons had l i t t l e e f f e c t on s i l i c a s t a b i l i z a t i o n effectiveness (see Table IX). In creasing the methyl acrylate content from 5% to 30% had also l i t t l e e f f e c t on s i l i c a fines s t a b i l i z a t i o n effectiveness. Acidizing substantially reduced the effectiveness of t h i s class of copolymer. Results for the i n j e c t i o n of 10,000 pore volumes of water indicated that s i l i c a fines elution from the t e s t column was s u b s t a n t i a l l y reduced on a long-term basis. The effectiveness of nonionic polymers as migrating clay s t a b i l i z e r s and the geometry of the adsorbed polymer - mineral complex may be substantially d i f f e r e n t for the nonionic polymers and the quaternary ammonium s a l t polymers. The observation that some quaternary ammonium s a l t polymers, while e f f e c t i v e swelling clay s t a b i l i z e r s , are i n e f f e c t i v e mineral fines s t a b i l i z e r s i s consistent with a d i f f e r e n t adsorbed polymer - p a r t i c l e complex geometry on d i f f e r e n t mineral surfaces. Monomer r e a c t i v i t y r a t i o s and thus comonomer sequence d i s t r i butions i n copolymers can vary with copolymerization reaction conditions. The comonomer d i s t r i b u t i o n could a f f e c t the geometry of the adsorbed polymer - mineral complex and the fines s t a b i l i z a t i o n properties. F i e l d Test

Results

Experiment 1. While there have been a number of reports concerning the effectiveness of quaternary ammonium s a l t polymers as swelling clay s t a b i l i z e r s i n c o n t r o l l i n g formation damage, the number of wells involved was usually too small for the comparison of r e s u l t s (between well treatments which u t i l i z e quaternary ammonium s a l t polymers and those which do not) to be s t a t i s t i c a l l y s i g n i f i c a n t . However, two sets of s t a t i s t i c a l l y s i g n i f i c a n t f i e l d r e s u l t s for the stimulation of a large number of wells i n the Fordache F i e l d (Pointe Coupee Parish, Louisiana) are available (19). The wells were completed i n the Wilcox W-8 and Sparta A formations. Average formation permeability was 8.6 and 180 m i l l i d a r c i e s respectively. Formation temperatures were 109°C (228°F) and 132°C (270°F) respec tively. Swelling and migration of s i l i c a t e mineral fines were c i t e d as the cause of rapid production declines i n these wells. The stimulation treatments were performed using retarded hydrofluoric acid. A t y p i c a l retarded hydrofluoric acid treatment consisted of: 1. 100 g a l / f t of perforated i n t e r v a l of aqueous 5% HCl 2. 50 g a l / f t of perforated i n t e r v a l of aqueous 3%HF/12% HCl 3. 25 g a l / f t of perforated i n t e r v a l of 2.8% NH^F (pH 7-8) A. 25 g a l / f t of perforated i n t e r v a l of aqueous 5% HCl 5. Repetition of steps 3 and A f i v e times



200,000 >1,000,000

1,000,000 1,000,000

70 70

95 70

23.8 9.5 14.3 9.5 38.1 14.3 59.5 55.0

0.40 0.45 0.19 0.20

b

C

41.2 50.0

44.1 50.0 44.1 47.1

S i l i c a Fines Production (% of untreated column) before 15% HCl a f t e r 15% HCl

0.20 0.19 0.19 0.19

Polymer Concentration (% by weight)

a. See reference 16 f o r experimental d e t a i l s . T = 62.8°C (145°F). b. Total fines production a f t e r i n j e c t i o n of 10,015 pore volumes fresh water. c. Total fines production a f t e r i n j e c t i o n of 10,502 pore volumes fresh water.

100,000 300,000 500,000 1,000,000

Polymer Molecular Weight

95 95 95 95

weight % DMAEMA

3

TABLE IX. EFFECTIVENESS OF DIMETHYLAMINOETHYLACRYLATE METHYL ACRYLATE COPOLYMERS AS SILICA FINES STABILIZERS



10.

BORCHARDT


219

6. 100 g a l / f t perforated i n t e r v a l of d i e s e l o i l or aqueous NH^Cl 7. the required volume of d i e s e l o i l , aqueous NH^Cl, or nitrogen to displace f l u i d s from the tubing. Average treatment volume was 600 gallons. A l l f l u i d s contained 1% (by volume) of water wetting non-emulsifier. The treatments u t i l i z i n g a c a t i o n i c organic polymer included the polymer i n a l l aqueous based f l u i d s . The reported polymer concentration of one percent by volume of the aqueous polymer solution as supplied. Active polymer concentration i s a c t u a l l y less than t h i s . When the clay s t a b i l i z a t i o n polymer was part of the well treatment, a non-ionic water wetting nonemulsifier was used. The f i r s t set of data i s for o i l production from 22 wells. A quaternary ammonium s a l t polymer clay s t a b i l i z e r was u t i l i z e d i n f i v e of the well treatments. Otherwise the 22 well treatment designs were i d e n t i c a l . Use of the clay s t a b i l i z e r i n 5 well treatments resulted i n a 131% production increase compared to a 156% increase a f t e r stimulation of 17 wells without clay s t a b i l i zer. Although the i n i t i a l o v e r a l l production response of the f i v e clay s t a b i l i z e r treated wells was l e s s , the o v e r a l l production decline rate was 4% per year compared to 16%/yr for the treatments which did not include the clay s t a b i l i z i n g polymer. This decline rate was determined for the period 4 to 24 months a f t e r well treatment. I t i s tempting to speculate that the lower i n i t i a l production response of the f i v e polymer treated wells was due to the formation of an adsorbed polymer layer which reduced formation permeability ( p a r t i c u l a r l y of the Wilcox Formation) s i g n i f i c a n t l y . Gas production from sixteen wells was also analyzed. Twelve retarded hydrofluoric acid treatments did not include the clay s t a b i l i z a t i o n polymer. The o v e r a l l gas production increase was 116% compared to an o v e r a l l increase of 200% obtained from four wells for which the clay s t a b i l i z a t i o n polymer was included i n the well treatment. With the exception of the use of the clay s t a b i l i z e r , the sixteen well treatment designs were i d e n t i c a l . Experiment 2. A c a t i o n i c organic polymer has also been evaluated as a mineral f i n e s s t a b i l i z e r i n a s t a t i s t i c a l l y s i g n i f i c a n t number of a c i d i z i n g treatments u t i l i z i n g hydrofluoric acid (20). This polymer was reported to remain c a t i o n i c i n both a c i d i c and basic media. Thus the c a t i o n i c s i t e s appear to be quaternary nitrogen atoms. This study involved twenty offshore Louisiana wells com pleted i n a Miocene sand having a formation temperature of 79 82°C (175° - 180°F). Wells i n t h i s area had a h i s t o r y of produc t i o n declines apparently caused by mineral fines migration. A large treatment volume, 18,000 - 28,000 gallons, was used to provide substantial r a d i a l penetration of the formation. The treatment design was: 1. 50 g a l / f t of formation 15% aqueous HCl containing 5% mutual solvent and 1% water wetting non-emulsifier and 50 lb/1000 gallons c i t r i c acid 2. 50 g a l / f t of formation aqueous 3% HF/12% HCl 3. 300 g a l / f t of formation aqueous retarded HF acid 4. the required volume of f l u i d required to displace a l l the acid from the tubing into the formation



220

OIL-FIELD CHEMISTRY

A corrosion i n h i b i t o r was present in a l l acid f l u i d s . Eight of the well treatments incorporated a cationic organic polvmer mineral fines s t a b i l i z e r i n the f i r s t three treatment stages. The active polvmer concentration was less than the reported aqueous polymer concentration of one percent (by volume). Again, t h i s was because the polymer was not supplied as a 100% active product. Production was monitored for 4-6 months after the stimulation treatments. Total o i l production from the twelve wells treated without the polymeric mineral fines s t a b i l i z e r (1100 bbl/day) was decreasing at a rate of 0.13%/day while the produced w a t e r : o i l r a t i o remained f a i r l y constant. The eight wells treated using the cationic organic polymer mineral fines s t a b i l i z e r exhibited a t o t a l o i l production of 7700 bbl/day which was increasing at a rate of 0. 32. per day. The water:oil r a t i o remained constant. The twelve wells for which no cationic organic polymer fines s t a b i l i z e r was used were exhibiting increasing gas production (0.15% per day) four to six months after the well treatments. This increase was due to the performance of one well from which gas production had more than doubled (from 1.46 MM scf/day to 2.14 scf/day). If t h i s well i s omitted from consideration, t o t a l gas production from the remaining wells was 4.92 MM scf/day and was decreasing at a rate of 0.06%/day. In contrast, t o t a l gas produc t i o n from the eight wells treated using the cationic organic polymer mineral fines s t a b i l i z e r , 3.39 MM scf/day, was increasing at a rate of 0.49%/day. Conclusions Results indicate that the effectiveness of quaternary ammonium s a l t polymers in s t a b i l i z i n g swelling clays and mineral fine p a r t i c l e s i s dependent on monomer chemical structure and polymer molecular weight. Long f l e x i b l e pendant sidechains containing quaternary nitrogen atoms appear to be required for these polymers to function as mineral fine p a r t i c l e s t a b i l i z e r s . Nonionic copolymers of N-vinylpyrrolidinone also functioned as mineral fine p a r t i c l e s t a b i l i z e r s . The results of two f i e l d experiments involving a s t a t i s t i c a l l y s i g n i f i c a n t number of wells indicated that quaternary ammonium s a l t polymers can function well as swelling clay and mineral fine p a r t i c l e s t a b i l i z e r s under actual f i e l d conditions. Literature Cited 1.

2.

3.

4.

Borchardt, J.K.; Roll, D . L . ; and Rayne L.M. Proceedings of the 55th Annual C a l i f o r n i a Regional Meeting of the Society of Petroleum Engineers, 1984, pp. 297-310, Paper No. SPE 12757 and references therein. G a b r i e l , G . A . ; Inamdar, G.R. Proceedings of the 56th Annual F a l l Technical Conference and E x h i b i t i o n of the Society of Petroleum Engineers, 1983, Paper No. SPE 12168. Reed, M . G . ; Coppel, C.P. Proceedings of the 43rd Annual C a l i fornia Regional Meeting of the Society of Petroleum Engineers, 1972, Paper No. SPE 4186. Muecke, T.W. J . Pet. Technol. 1979, 31, 144.


10.


5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

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K h i l a r , K . C . ; Fogler, H.S. Soc. Pet. Eng. J., 1983, 23, 55. McLaughlin, H.C.; Weaver, J . D . U.S. Patent 4 366 071, 1982. McLaughlin, H.C.; Weaver, J . D . U.S. Patent 4 366 072, 1982. McLaughlin, H.C.; Weaver, J . D . U.S. Patent 4 366 073, 1982. McLaughlin, H.C.; Weaver, J . D . U.S. Patent 4 366 074, 1982. Anderson, R.W.; Kannenberg, B.G. U.S. Patent 4 158 521 (1979). Lancaster, J.E.; Baccei, L.; Panzer, H.P. J . Polym. S c i . Polym. L e t t . Ed., 1976, 14, 549. Smith, C.W.; Borchardt, J . K . U.S. Patent 4 393 939, 1983. H a l l , B . E . World O i l December, 1986, 49. Borchardt, J.K.; Young, B.M. U.S. Patent 4 A97 596, 1985. Borchardt, J.K.; Young, B.M. U.S. Patent 4 536 305, 1985. Borchardt, J.K.; Young, B.M. U.S. Patent 4 558 741, 1985. Borchardt, J . K . U.S. Patent 4 536 303, 1985. Borchardt, J . K . U.S. Patent 4 563 292, 1986. Holden,III, W.W.; Prihoda, C . H . ; Hall, B . E . J . Pet. Technol., 1981, 33, 1485. Presented at the 55th Annual C a l i f o r n i a Regional Meeting of the Society of Petroleum Engineers and available as an addendum to reference 1.

RECEIVED November 28, 1988


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