3

GEOTHERMAL RESERVOIR WELL STIMULATION PROGRAM

ACIDIFICATION OF GEOTHERMAL WELLS LABORATORY EXPERIMENTS

Prepared for

U . S . DEPARTMENT OF ENERGY

CONTRACT NO. DE-AC04-79AL10563

VETTER RESEARCE - \

r, JANUARY 1982

I

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REPUBLIC G E O T H E W , INC. 11823 EAST SLAUSON AVENUE

SANTA FE SPRINGS, CALIFORNIA 90670 W

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

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TABLE OF CONTENTS (CONTINUED)

PAGE .

8.2.1 8.2.2 8.2.3 8-2.4 8.2.5 8.2.6

CALCIUM CARBONATE .............. KAOLIN ......................... S E P I O L I TE ...................... DESERZ PEAK F O W T I O N MATERIAL, . RDOSEVELT ROT SPRINGS FORMATION SIGNIFICANCE OF L I Q U I D ANALYSIS

......... ......... ......... ......... W R I A L .........

......... ......... ......... ......... ......... ......... 8.3 ANALYSIS OF SOLIDS FROM COOLED L I Q U I D REACTION PRODUCTS . 8.4 SCANNING ELECTRON MICROSCOPY ............................

9.0

10.0

PROBLEMS ASSOCIATED WITH THE ACID TESTS ...................... RECOMMENDATIONS FOR FUTURE A C I D I Z I N G WORK ....................

11.0 SCALE I N R I B I T O RS ............................................. 11.1 11.2

MAJOR SCALISG C O W UNDS .................................. POTENTIAL INHIBITORS FOR CaLCIUM CARBONAT& SCXLE ........

11.3 FIYDROTHERMAI, S T A B I L I T Y .................................. 11.3.1

11.3.2

HYDROTHERMAL STABILITY OF THE "AS RECEIVED"

KYDROTXERPU STABILITY OF THE RECEIVE NEUTRALIZED I N N I B I T O R ............................ ~ I B I T O R ........................................

11.4 RECOMMNDATIONS I N APPLYING IBHIBITORS ................... TclBLES .............................................................. E f G ~ S .............................................................

11 11 11 12 12 12

13 13

14

14

15

15 15 16

17

17

17

19

32

c PREAMBLE

Republic Geothermal, Inc. (RGI) is t h e prime c o n t r a c t o r under DOE/DGE Contrac t No. DE-AC04-79AL10563. This c o n t r a c t is concerned with the s t i m u l a t i o n of geothermal r e s e r v o i r wells. Verter Research (VR) is a subcont rac tor f o r R G I and is charged wi th chemical and material i n v e s t i g a t i o n s and eva lua t ions under t h i s DOEDGE prime c o n t r a c t . under t h i s pr ime c o n t r a c t No. DE-AC04-79AL10563.

One of VR's s p e c i f i c t a s k s under t h i s p r i m e c o n t r a c t is t o develop and conduct l abora to ry procedures r e l a t e d t o a c i d i z i n g of geothermal w e l l s . f u l f i l l s VR's o b l i g a t i o n under t h i s s p e c i f i c task .

W

VR is managing subcont rac t DE-AC04-79AL10563-VR

G This r e p o r t

1.0 ABSTRACT

This r epor t desc r ibes the labora tory t e s t i n g of the r eac t ions of a c e t i c , formic, hydrochlor ic , and hydrofluoric ac ids with calcium carbonate, kao l in , s e p i o l i t e , and two formation ma te r i a l s a t geothermal temperatures.

I n genera l , a workable t e s t procedure was developed which provided information regarding the relative r e a c t i v i t i e s of se lec ted minerals or formation

Tes ts with hydrochlor ic ac id were complicated by r eac t ions of t he acid with the t e s t ves se l m a t e r i a l s and the re fo re , only very l imi t ed work could be done with t h i s acid a t t he des i r ed temperatures. I n s p i t e of t hese d i f f i c u l t i e s , information regarding t h e amount of so lub le ma te r i a l i n t he var ious ac ids was obtained. From t h i s information an approximate va lue f o r t he percent d i s s o l u t i o n of t h e minera ls

information regarding the formation of s o l i d secondary r eac t ion products upon cool ing of t h e reacted acid was a l s o obtained. The impl ica t ion of t h e mineral r e a c t i v i t i e s with t h e d i f f e r e n t ac ids and the formation of secondary s o l i d s on geothermal ac id i z ing opera t ions a r e discussed.

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u - materials with t h r e e of t h e four ac ids inves t iga ted .

13 under the d i f f e r e n t r e a c t i o n condi t ions could be ca lcu la ted . Addit ional

v

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I n add i t ion , some se l ec t ed &ale i n h i b i t o r s ( f o r calcium carbonate) were t e s t e d f o r t h e i r hydrothermal s t a b i l i t y . formation of calcium carbonate s c a l e before and a f t e r aging a t 500°F was measured. recommendations f o r t h e i r u se i n the f i e l d a r e discussed.

2.0 CONCLUSIONS

Their e f f i c i ency i n i n h i b i t i n g the

The impl ica t ions of t he loss of e f f i c i ency of these ma te r i a l s and

1. From t hese tests a c e t i c acid w a s found t o be the bes t a t d i s so lv ing CaC03. (However, HC1 was not t e s t ed with CaC03; s e e s e c t i o n 8.2.1.)

2. Hydrofluoric acid d isso lved considerably more s e p i o l i t e and formation w m a t e r i a l s than t h e a c e t i c or formic ac ids .

3. Formic acid d isso lved more kao l in than the HF or a c e t i c ac ids .

4. Formic acid s e l e c t i v e l y leached aluminum, a c e t i c acid s e l e c t i v e l y leached calcium, and hydrof luor ic ac id s e l e c t i v e l y leached t h e s i l i c a .

62

5 . I n genera l , increas ing acid concent ra t ions brought about increased -. mineral d i s so lu t ion .

6. Increasing temperature increased the mineral d i s s o l u t i o n wi th HF @ -

acid. Mineral s o l u b i l i t i e s i n e i t h e r a c e t i c o r formic ac ids sometimes increased and a t o the r t imes decreased with increas ing temperature. These r e l a t i o n s were dependent on both the mineral being reac ted and t h e acid being evaluated.

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than HF acid.

7 . Only one test w a s completed with HCL. This test showed t h a t H C l d i sso lved more Desert Peak formation than e i t h e r a c e t i c or formic a c i d s but much less

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8 . A l l of the f i l t e r e d , reacted ac ids formed p r e c i p i t a t e s upon cool ing.

9. Secondary d e p o s i t s were found adhering t o the formation ma te r i a l s a f t e r completing the t e s t except t he H C l t r ea t ed Desert Peak ma te r i a l . t he t e s t a t e levated temperatures o r a f t e r cooling.

10. The s c a l e i n h i b i t o r s t e s t ed a r e thermally l e s s s t a b l e i n the "as received" form, e s p e c i a l l y i f they a r e ac id i c .

It i s unknown a s t o whether these depos i t s formed during

11. I f t h e "as received" s c a l e i n h i b i t o r i s a c i d i c , i t should be neu t r a l i zed f o r b e t t e r t h e m a l i s t a b i l i t y .

3.0 RECOMMENDATIONS

Before any f u r t h e r d e f i n i t i v e acid work can be done a t geothermal temperatures, a thorough study must be undertaken t o f ind adequate m a t e r i a l s t o cons t ruc t t h e t e s t ves se l s . The da ta provided from the manufacturers i s l imi ted to temperatures of about 212OF. Therefore, any acid r e s i s t a n c e d a t a regarding m a t e r i a l s of cons t ruc t ion a t higher temperatures would have t o be gathered experimental ly before any f u r t h e r acidfmineral t e s t s can take place.

4.0 PURPOSE OF LABORATORY WORK - - The purpose of t h i s labora tory work i s t o determine i f the c u r r e n t l y a v a i l a b l e techniques f o r acid s t imu la t ion of o i l and gas wells can be extended t o geothermal opera t ions . voluminous, bu t no re ferences t o acid work a t geothermal temperatures could be found. Therefore, i t was decided t h a t f o r t h i s con t r ac t a l imi ted number of experiments would be run t o he lp d e l i n e a t e any app l i ca t ions o r problems i n t r a n s f e r r i n g o i l f i e l d technology t o geothermmal operat ions.

The main purposes of t he study of acid-rock i n t e r a c t i o n s under simulated r e s e r v o i r and wel lbore condi t ions a r e t o determine:

The l i t e r a t u r e on low temperature acid s t imu la t ion i s

1. The d e t a i l s of the materials, experimental set-ups, and labora tory procedures to be used.

The s u i t a b i l i t y of some of the se l ec t ed labora tory methods ( a ) t o support t h e s e l e c t i o n of acid s t imu la t ion methods i n the f i e l d and (b ) t o a id t h e eva lua t ion of ac tua l f i e l d jobs.

Spec i f i c types and concent ra t ions of a c i d s t o be used on s p e c i f i c minerals .

2.

3 .

4. Effec t of temperature on the acid-mineral r e a c t i v i t i e s .

5 . The i d e n t i t y and poss ib l e de t r imenta l e f f e c t s of secondary depos i t s . I I

This study c o n s i s t s of two ( 2 ) main parts:

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1. Determine the r e l a t i v e chemical r e a c t i v i t y of a t l e a s t four ac ids ( a c e t i c , formic , hydrochlor ic and hydrofluoric ac id) on various types of r e s e r v o i r ma te r i a l .

2. Inves t iga t e the na td re of some of t he by-products of t he chemical rock-acid r eac t ions.

_*

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This l ab work was by necess i ty designed (and modified during the t e s t i n g ) t o a t tempt the genera t ion of some guide l ines f o r s e l ec t ing s p e c i f i c ac ids t o be used in f i e l d jobs i n a t imely manner. Therefore, an abbreviated matr ix (shown i n Table 1 ) was designed f o r t h i s purpose and was not intended t o be an in-depth s tudy of t h e r e a c t i o n k i n e t i c s 'or s o l u b i l i t y c h a r a c t e r i s t i c s of rock/acid i n t e r a c t i o n s . screening of problems t o be expected during.planned or suggested f i e l d jobs.

7-

This matr ix was designed t o a l low a r a t h e r quick

5.0 TEST EQUIPMENT - The t e s t equipment used i n t h i s s tudy c o n s i s t s of :

. 1. Test c e l l s

2. Various mechanical and e l e c t r o n i c support equipment

3. Analy t ica l equipment

This t e s t equipment i s descr ibed i n the following paragraphs.

5 . 1 TEST CELLS -- The t e s t c e l l used f o r t he acid/rock i n t e r a c t i o n s i s shown i n Figure 1. c e l l was o r i g i n a l l y designed t o be usefu l f o r var ious types of exper izents involving b r i n e s , ac ids and rocks a t high temperatures. It c o n s i s t s of t h r e e (3) high pressure r e a c t i o n v e s s e l s connected by a "Tee". These v e s s e l s were manufactured by Autoclave Engineers. The wetted par t s were constructed from Haste l loy C which i s known t o have an exce l l en t cor ros ion r e s i s t a n c e t o high temperature b r ines . r e s i s t a n c e i n a c i d s a t temperatures up t o 100OC. materials of cons t ruc t ion and assoc ia ted problems are descr ibed i n t h e next sec t ion . A f i l t e r d i s c of s in t e red Has te l loy C i s placed a t t h e en t rance t o one of the arms of the three-arm arrangement. i s t o sepa ra t e t h e suspended s o l i d s from l i q u i d s .

5 . 1 . 1 MATERIAL SELECTION FOR THE HIGH

The

Hastel loy C a l s o was reported to have good cor ros ion D e t a i l s of s e l e c t i n g t h e

The purpose of t h e f i l t e r d i s c

c_-- TEMPERATURE TEST CELLS -- There a r e severa l f a c t o r s t o be taken i n t o cons idera t ion before s e l e c t i n g t h e m a t e r i a l s of cons t ruc t ion f o r labora tory hardware t o be used a t high temperatures with a c i d s and brines. a r e a s follows:

Some of the most important cons idera t ions

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1. Corrosion resistance of the materials.

2. Availability of the material in appropriate shapes and dimensions.

3. Ease of machining to the close tolerances required for high pressure equipment .

4. Availability of the various fittings that are specific to the test cell configuration.

Ease of assembling and disassembling of the test cell. 5 . I

6.

7.

Time required to acquire various parts for the test cell.

Cost*of materials and the construction of the apparatus.

Selecting the metal to use for corrosion resistance to acids at high temperatures proved to be very difficult since the manufacturer had no data on acid corrosion above 100OC. Therefore, the material selection had to be based on the available lower tempe,rature acid data and high temperature brine data.

A survey of the current activity in acid testing indicated that many workers are using very exotic equipment such as gold- or platinum-coated materials, specially constructed glass-lined vesselg, and passivated metals of various types. But it was also found that none of these workers were experimenting at geothermal temperatures. Since these exotic materials are very expensive and time consuming to make, it was decided to run our tests with readily available materials. Five materials were chosen for further evaluation. These materials were Hastelloy B, Hastelloy C, titanium, zirconium, and tantalum. The use of tantalum was immediately discarded due to its unavailability. titanium cells were constructed based on their brine stability but were not used in these tests since it was felt they would not maintain a high pressure seal as effectively as the other metals. Hastelloy B is a nickel based metal with a lower chromium content than Hastelloy C. The manufacturer's literature on Hastelloy B shows no obvious advantage for using Hastelloy B over Hastelloy C. Therefore, Hastelloy B c e l l s were not used for these tests. Table 3 shows some blank acid tests on Hastelloy B.

Some

--

5.1.1.1 HASTELLOY C

Hastelloy C is a nickel-based alloy with the following composition: 6% Fe, 17% Cr, 19% Mo, 0.1% Si, 1% Mn, 5% W. Several test cells were made of Hastelloy C. against all concentrations of brine at higher temperatures. From the literature supplied by the manufacturer (Cabot Corporation, Satellite Division), it appears that the corrosion rate is approximately the same for all brine concentrations for a fixed temperature. Since the maanufacturer supplied only acid corrosion data to about 100°C, this data was extrapolated quadratically to determine the corrosion rate of Hastelloy C at higher temperatures. The rate was estimated to be in the range of 5000 mpy at 225OC. Even though the corrosion rate seemed to be high, it was felt that any 24-hour acidification test conducted at a fixed temperature could be compared by adjusting the resultant data for Hastelloy C dissolution determined in a

51X Ni,

Hastelloy C is known to have an excellent corrosion resistance

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"blank acid" experiment. products i n HC1 and HF ac ids .

-- Table 3 shows the ana lys i s f o r these d i s s o l u t i o n

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5.1.1.2 ZIRCONIUM

Af ter i t was found from the tests ( s e e sec t ions 8.1 and 9.0) t h a t Hastel loy C was unsu i t ab le f o r use with HC1 ac id , work was s t a r t e d with zirconium. Zirconium is used ex tens ive ly i n the nuclear power p lan t indus t ry so i s somewhat more a v a i l a b l e than most o the r exo t i c metals. zirconium has an k c e l l e n t r e s i s t a n c e t o cor ros ion i n HC1 a t a l l concent ra t ions a t 225OC. i s reported by t h e manufacturer. The o the r requirements f o r ma te r i a l s e l e c t i o n mentioned e a r l i e r , such as machinabi l i ty , were quest ionable . However, i n order t o proceed with a c i d i f i c a t i o n tests, some ba r s tock of a zirconium alloy (4.5X maximum of Hafnium) was purchased and two t e s t assemblies made. s i g n i f i c a n t leaking a t t he s e a l s was encountered. b e t t e r s e a l s were unsuccessful due t o the so f tnes s of t he a l loy . Adequate

As mentioned e a r l i e r ,

A corros ion rate of l e s s than f i v e ( 5 ) m i l s per year

Upon heat ing the v e s s e l s containing HC1 t o temperature, Repeated e f f o r t s t o machine

tes t v e s s e l s could not be made. A f u r t h e r d i scuss ion of the zirconium c e l l i s found i n a l a te r s e c t i o n with some recommendations f o r f u t u r e e f f o r t s i n t h i s a rea .

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6 5.1.2 HIGH PRESSURE SEALING OF THE TEST CELL - v - 7 -

The Hastel loy C pressure v e s s e l s manufactured by Autoclave Engineers c o n s i s t o f 314-inch pipe n ipples using a s p e c i a l sea l ing arrangement a s shown i n F igu re 2. The metal-to-metal s e a l i s made by a s p e c i a l l y machined j o i n t held i n p lace by a gland nut t ightened t o 125 foot-pounds. I f t he s e a l s a r e made up properly, any f a i l u r e s t h a t occur a r e usua l ly due t o e r ros ion or cor ros ion a t the metal-to-metal contac t . Therefore, these contac t a r eas must be examined a f t e r every t e s t .

Two ends of t he three-arm c e l l a r e covered by blank end caps. The o t h e r arm i s f i t t e d wi th a va lve f o r withdrawing the f i l t e r e d reacted acid. This va lve is a l s o constructed with a l l wetted p a r t s cons i s t ing of Hastel loy C. These va lves and a l l the s e a l s of t h e three-arm c e l l are r a t ed t o at least 10,000 p s i .

6.0 TEST PROCEDURES

To ob ta in t h e d a t a contained i n t h i s r e p o r t , the following procedures were used. A s shown i n Figure 1, one arm of t h e three-arm t e s t ce l l w a s f i l l e d with t en grams o f t h e s o l i z t o be t e s t e d . 25 m l of t he acid t o be used. In a l l cases , t h i s gave a g r e a t e r amount of r e a c t i v e s o l i d present than acid. Therefore, a l l the acid would be spent a f t e r t he test was completed. The c e l l was then placed i n an oven i n s p e c i a l l y b u i l t ho lders a t tached t o a mechanical arrangement. t h a t would g ive a rocking motion t o t

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The middle ann was then f i l l e d with

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m a t e r i a l s as the r e a c t i o n was taking p lace ( s e e Figure 3 ) -

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6.1 TEST CELL MODIFICATION -- Afte r i t was found t h a t t he ac ids dissolved more of t he Hastel loy C metal than was expected, a t t e m p t s were made t o e l imina te the acid contac t with the metal . These at tempts included spraying a coat ing on t he i n s i d e of t he c e l l s , t ry ing t o pas s iva t e the metal with o the r ac ids , and making i n s e r t s for the arms of t h e c e l l , Eliminating t h e acid/metal contac t was found t o be impossible but by using Teflon tubing i n s e r t s , i t was f e l t t h a t t he acid/metal contac t t i m e could be minimized. These i n s e r t s were made by boring out a so l id cy l inde r o f Teflon t o make a "thimble" t h e same length and diameter as t he arm of the test c e l l .

These Teflon inserts were made t o f i t , a i t i g h t l y as poss ib le , i n t o t h e arms t h a t contained t h e a c i d s and the minerals , thereby e l imina t ing d i r e c t contact of t he acid on t he metal during heat ing. except f o r t he HCl . HC1; va lves was ocurr ing. 8.2.4) and no f u r t h e r HC1 work was attempted.

TEFLON INSERT DIFFfCULTSES

This did he lp on a l l t he ac ids The d i s s o l u t i o n of t h e Hastel loy C was s t i l l high with

and etching of t h e metal c l o s e t o the high pressure s e a l and i n the Therefore, only one HC1 test was completed (see Sec t ion

6 2 - The use of t h e Teflon i n s e r t caused another problem i n t h a t Teflon tends t o flow a t t he t e s t temperatures being used so t h a t the i n s e r t would p a r t i a l l y co l l apse , making i t extremely d i f f i c u l t t o recover the reacted mineral . Therefore , no accu ra t e measurements could be made d i r e c t l y on the amount of mineral d i sso lved . Attempts were made, however, t o c a l c u l a t e t h i s va lue by ana lyses of t he spent a r i d (Table 9 ) . --

6.3 SAMPLE HEATING

The e n t i r e c e l l was then heated r a i s i n g the temperature of each ind iv idua l t e s t component t o the des i r ed t e s t temperature with the rocking motor turned o f f . The c e l l was then t ipped ( s t i l l a t t h e test temperature) so t h a t t he ac id would run i n t o t h e s o l i d s compartment and mix with the s o l i d mater ia l . Then the motor w a s turned on and t h e mixed acid and s o l i d s were allowed t o r e a c t overnight (16 hours) a t t h e test temperature.

6 . 4 FILTERING THE REACTED SAYPLE - The next s t e p was to t i p the e n t i r e c e l l 180' so t h a t t he reacted l i q u i d would f a l l onto the f i l t e r d i s c ( s e e Figure 1). A f i v e ( 5 ) l i t e r con ta ine r of cold water was then placed around t h e empty-arm o f t h e c e l l (below t h e f i l t e r d i s c ) t o c r e a t e a vacuum from cool ing so t h a t t h e r e a c t i o n products would be pul led through t h e f i l t e r d i s c . s ize .

The f i l t e r d i s c i s about 20 t o 40 microns i n pore

6.5 CELL DISASSEMBLY AND SAMPLE COLLECTION - -- Afte r cool ing the c e l l t o t o m temperature, i t was placed i n a v i s e with the va lve end pointed down. was co l l ec t ed . f i l t e r i n g the l i q u i d through t h e f i l t e r d i sc .

The va lve was opened and the f i l t e r e d r e a c t i o n l i q u i d This volume would vary depending on the e f f i c i e n c y of

The average volume through w a s

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e

G

about 10 t o 1 2 m l . This arm of the t e s t c e l l was then removed from the t e e and r insed t o c o l l e c t any s o l i d mater ia l t h a t might have adhered t o it . o t h e r two arms were then disassembled and cleaned, the reacted s o l i d s being saved f o r f u r t h e r ana lys i s . determine the weight loss of t h e s o l t d s from acid degradation. mentioned i n Sec t ion 6.1.2, i t was found t h a t t he s o l i d s recovery was not very e f f i c i e n t due t o co l l aps ing o f t h e Teflon i n s e r t s , and meaningful weight l o s s numbers could not be obtained.

The

Or ig ina l ly the reacted s o l i d s were weighed t o But a s .

6.6 ANALYSIS*OF COLLECTED SAMPLES - Three (3) types of samples were co l l ec t ed from these tests. These were the r eac t ed s o l i d material, t h e f i l t e r e d r eac t ion l i q u i d , and the s o l i d s f i l t e r e d from the l i q u i d a f t e r cool ing.

6.6.1 REACTED SOLIDS - Most of t he reac ted s o l i d s w e r e saved and se lec ted samples were examined by scanning e l e c t r o n microscopy (SEMI. The purpose of t h i s examination was t o i d e n t i f y any changes t h a t occurred i n the s o l i d ma te r i a l from the acid r e a c t i o n s and to perhaps i d e n t i f y any r e a c t i o n products l e f t behind on t he s o l i d s .

6.6.2 FILTERED REACTION LIQUID

The f i l t e r e d r e a c t i o n l i q u i d s ( f i l t e r e d a t t he t e s t temperature) were i n i t i a l l y submitted f o r chemical a n a l y s i s i n order t o determine the metals conten t of t h e f i l t r a t e .

The f i r s t a n a l y s i s cons is ted of determining 36 d i f f e r e n t ions but a s t he t e s t i n g proceeded, i t was determined t h a t only about s i x of t hese were r e l even t t o these tests. Therefore, only sodium, magnesium, calcium, s i l i c a t e , aluminum, and i r o n were t e s t ed f o r and reported i n subsequent samples.

6.6.3 SOLIDS FROM COOLED REACTION LIQUID - Afte r reaqhing room temperature, t he f i l t e r e d r e a c t i o n l i q u i d s usua l ly contained ' s o l i d s t h a t had ev ident ly p rec ip i t a t ed upon cool ing. These s o l i d s ( c a l l e d secondary depos i t s ) were c o l l e c t e d , weighed, and se lec ted ones examined f o r i d e n t i f i c a t i o n by e l e c t r o n microprobe analyses. The r e s u l t s of t h e microprobe a n a l y s i s are shown i n Table 10. q u a n t i t a t i v e but does show t h e r e l a t i v e amounts of each element present . element l i s t e d f i r s t occurred i n a higher concent ra t ion than those following it in t he l i s t .

This a n a l y s i s i s not .- - The

Since t h i s a n a l y s i s showed a l a r g e amount of t h e metal d i s s o l u t i o n products ( i . e . , Ni, C r , Mol, no at tempt was made t o r ed i s so lve the s o l i d and analyze q u a n t i t a t i v e l y . The weight percent of t hese secondary depos i t s from the f i l t e r e d l i q u i d were taken and are shown i n Table 11. --

~

it

v

7.0 MATERIALS TESTED

-- Table 1 shows the matrix design f o r the ac id iz ing lab work. minerals and two formation m a t e r i a l s were reacted with four d i f f e r e n t ac ids ( a t two concent ra t ions) a t two temperatures. These t w o p a r t i c u l a r formation m a t e r i a l s were chosen f o r t e s t i n g because they represent t he f i e l d s se l ec t ed as prime candidates f o r a c i d k i n g .

7

Three "pure"

This r e su l t ed i n 160 t e s t s . G

7.1 CALCIUM CARBONATE

Calcium carbonate (CaC03) i s found i n na ture a s c a l c i t e , marble, l imestone, coral, chalk, s h e l l s of mollusks, e t c , D r i l l i n g and o i l and gas production can take p lace i n any of t hese forms of 'CaC03. forming calcium c h l o r i d e and l i b e r a t i n g C02. The calcium carbonate (CaC03) used w a s a f i n e mesh (100 through 300 mesh).USP grade p rec ip i t a t ed powder suppl ied by Mallinckrodt. formula weight of 100.09.

G

It i s r e a d i l y d isso lved by HC1

v As suppl ied, i t i s a r e l a t i v e l y pure CaC03 with a

7.2 KAOLIN

i Kaolin i s a n a t u r a l l y occur;ing c l a y material a l s o known as, China Clay.. Kaolin is an a lumino-s i l ica te formed by t h e weathering and breaking down of minerals such as f e ldspa r and neph i l i t e . I t s formula i s A1203.2Si02.2H20. The kao l in used i n the tests i s a N.F. grade fine-mesh powder supplied by Mallinckrodt.

63

7.3 SEPIOLITE

S e p i o l i t e is a complex hydrous magnesium s i l ica te c l ay - l ike masses and i s a l s o known a s meerschaum. 2Mg0.3Si02.2H20. The sample used f o r these t e s t s m a t e r i a l used i n high temperature d r i l l i n g f l u i d s by I n d u s t r i a l Mineral Ventures Inc. , and obtained Flu id Serv ices , Inc., Brawfey, Cal i forn ia .

occurr ing n a t u r a l l y i n

i s an i n d u s t r i a l grade . It was mined and packaged from Profess iona l D r i l l i n g

Its formirra i s

7.4 DESERT - PEAK FORMATION MATERIAL

. This i s a n a t u r a l l y occurr ing formation ma te r i a l obtained from c u t t i n g s submitted by R G I from a wel l d r i l l e d i n t h e Desert Peak KGRA; Churchi l l

i l l i t e , and c h l o r i t e based on t h e x-ray d i f f r a c t i o n pa t t e rn , received was a heterogeneous mixture of severa l rock types which was obvious from a v i s u a l observa t ion of t h e samples.

6 County, Nevada, This m a t e r i a l , c a l l e d a "greenstone," contained k a o l i n i t e , The ma te r i a l as

7.5 ROOSEVELT - HOT SPRINGS FORMATION MATERIAL

This i s a n a t u r a l l y o c c u r r i submitted by R G I from a well d r i l l e d i n t h e Roosevelt Hot Springs KGRA, Beaver County, Utah. composed mainly of a l k a l i f e ldspa r and quar tz with some mica. i s appl ied t o ma te r i a l t h a t was e jec ted from a volcanic e rupt ion as ash.

formation ma te r i a l obtained from c u t t i n g s

This ma te r i a l i s c a l l e d a r h y o l i t i c t u f f and i s f i n e gra ined , The term t u f f

7.6 ACID SAMPLES - Four d i f f e r e n t acid types were used for these t e s t s . acid (HCl), hydrof luor ic acid (HF), a c e t i c acid (CH3COOH), and formic acid (HCOOH). i n T a b l e 1.

They were hydrochlor ic

Each of t hese ac ids were a l s o used a t two concent ra t ions a s l i s t e d c

--

c

c;,

HC1 i s the most widely used acid i n o i l f i e l d s t imu la t ion due t o i t s proven e f f e c t i v e n e s s i n t r e a t i n g formations economically. co r ros ion i n h i b i t o r . ' However, i t was f e l t t h a t due t o the l imi ted t i m e t h a t t e s t i n g with an i n h i b i t o r would not be done. meet s p e c i a l problems encountered i n wellbore s t imula t ions . used in combination wi th HC1 f o r i t s a b i l i t y t o a t t a c k s i l i c a and s i l i c a t e s . Acet ic and formic ac ids are usua l ly used when long contac t times with metals cannot be avoided s ince these ac ids have a f a r lower cor ros ion r a t e with most meta ls than e i t h e r HCl o r €IF. H C l as 8 re ta rded ac id for high temperature wells.

Table 2 shows t h e a n a l y s i s of t h e ac ids used f o r t h i s work. contamination i n any of t hese a c i d s was the r e l a t i v e l y high sodium (Na) l e v e l s i n the a c e t i c and formic acid$.

8.0 TEST RESULTS

It i s usua l ly used with a

The o the r ac ids a r e only used t o EIF i s usua l ly

Formic acid is usua l ly used i n combination with

The only se r ious 7-

- The following sec t ions show t h e r e s u l t s of the ana lys i s performed as previous ly descr ibed .

8.1 BLANK ANALYSIS 7

Cj

Table 3 shows t h e r e s u l t s of t he ana lys i s of t he var ious ac ids a f t e r r eac t ing with empty test c e l l s . Has te l loy B. As can be seen, t h e major de t r imenta l e f f e c t s were seen from t h e HC1 r eac t ions . Vast amounts of n i cke l , chromium, i ron , and aluminum and s u b s t a n t i a l amounts of t h e o t h e r c a t i o n s were dissolved from the test c e l l s by t h e HCL. This raises the concern t h a t the d i s s o l u t i o n products from the HC1 w i l l i n t e r f e r e w i t h e i t he r the acid/mineral r eac t ions o r the ana lys i s f o r t he acid/mineral r e a c t i o n products.

The HF ac id d isso lved s u b s t a n t i a l amounts of s i l i c a , aluminum, molybdenum, and sodium but not near ly a s much a s d id the HC1. disso lved only r e l a t i v e l y small amounts of t hese ions. t e s t e d and w a s found t o be impervious t o e i t h e r HC1 or HF.

-- The metals used i n these t e s t s were Hastel loy C and

6J

The a c e t i c and formic a c i d s Zirconium was a l s o

6

These tests are t h e blanks f o r a l l subsequent tests and these concent ra t ions o f dissolved ions were subt rac ted from all t he o t h e r t a b l e s of r e s u l t s i n t h i s r epor t . 6

8.2 ANALYSIS OF FILTERED L I Q U I D REACTION PRODUCTS

Tables 4 through 8 show the r e s u l t s of analyzing the f i l t e r e d reac ted ac id . All res'Zits are rTported a s mg/L of the ind iv idua l ions found i n t h e l i q u i d . These r e s u l t s a r e cor rec ted f o r t he blank ana lys i s l i s t e d i n 7- Table 3.

6 It was

;ri found t h a t the major ions involved i n the d i s s o l u t i o n of the minerals t e s t ed a r e sodium, magne.sium, calcium, s i l i c a t e s ( repor ted as s i l i c a ) , aluminum and i ron .

This dissolved s o l i d s ana lys i s r e l a t e d d i r e c t l y t o the amount of mineral d i s s o l u t i o n and should show the r e l a t i v e e f f ec t iveness of the a c i d ' s a b i l i t y t o d i s s o l v e t h a t p a r t i c u l a r mineral . th rou h 8 are d e s c r i p t i v e and graphic rankings of each of the t e s t ed az ids on d p g c t i v e minfrrals.

G The next paragraphs and Figures 4

G

G

8.2.1 CALCIUM CARBONATE a

Figure 4 and Table 4 shows t h e t o t a l ion content of the f i l t e r e d l i q u i d a f t e r t h e r e a c t i o n of a c e t i c and formic acid with calcium carbonate. HF and HC1 were not run with calcium carbonate. The HF was not run due t o i t s well-known formation of t he in so lub le p r e c i p i t a t e calcium f luo r ide , and the HCL was not run due t o t h e previously mentioned r eac t ion with the t e s t ves se l s . This p l o t i n d i c a t e s t h a t t he formic acid d i s so lves more mater ia l than the a c e t i c e s p e c i a l l y at 225" C. Most of t h e ion t o t a l f o r t he formic acid came from magnesium, aluminum, and s i l i c a t e ions which occur only i n t h i s calcium carbonate i n very l o w l e v e l s as contaminants. ev iden t ly p r e f e r e n t i a l l y reacted with those elements r a t h e r than with the mass of the calcium. calcium i n s o l u t i o n ind ica t ing more r e a c t i v i t y with the calcium carbonate. In e i t h e r case , more ma te r i a l was d isso lved a t 225°C than a t 175°C.

--

Therefore, the formic acid

The a c e t i c ac id on the o t h e r hand had higher l e v e l s of

8.2.2 KAOLIN

Figure 5 and Table 5 show the t o t a l dissolved ions a f t e r r eac t ion with the c l a y mineral kaolin: Again, HC1 was not used. '

I n t h i s case t h e formic acid a t 175°C provided more dissolved ma te r i a l than t h e HF from s i l i c a t e and aluminum. d isso lved s o l i d s while the a c e t i c acid produced only r e l a t i v e l y minor amounts. A b i g d i f f e r e n c e with t h i s r e a c t i o n i s t h a t t he formic acid seemed t o d i s s o l v e more ma te r i a l a t 175°C than a t 225°C.

Both the HF and formic ac ids dissolved l a r g e amounts of s i l i c a from the kaol in . This i s s i g n i f i c a n t s ince kao l in i s an a lumino-s i l ica te ma te r i a l .

8.2.3 SEPIOLITE

6

The HF acid a l s o had r e l a t i v e l y high

43

However, t he formic acid a l s o dissolved l a r g e amounts of aluminum.

66,

Figure 6 and Table 6 show t h e t o t a l ion conten t of t he acid a f t e r r e a c t i o n wi th the c l a y ma te r i a l s e p i o l i t e . mineral .

Hydrofluoric acid produced by f a r the most ma te r i a l i n so lu t ion , and as expected, a l l s i l i c a t e . Also, formic acid seemed t o be more r e a c t i v e than a c e t i c ac id . Again, t he h igher temperature (225°C) produced the most d i sso lved ma te r i a l . It i s i n t e r e s t i n g t o no t h a t the formic acid did not d i s s o l v e a s much s e p i o l i t e 8s i t did kaol in . s i l i c a t e while kao l in i s an alumino-si l icate .

- T The H C l again, was not reacted with t h i s

G

S e p i o l i t e i s a magnesium 6 Comparing d a t a from the two

G

s

e

analyses show t h a t formic acid p r e f e r e n t i a l l y d i s so lves the aluminum compound s .

8 . 2 . 4 DESERT PEAK FORMATION MATERIAL - Figure 7 and Table 7 show the t o t a l ion concent ra t ion a f t e r the acid r eac t ions with the Desert Peak formation mater ia l s . A l l four ac ids were t e s t ed with t h i s ma te r i a l , t h e HCL only a t 175°C.

--

It w a s observed t h a t HF had t h e h ighes t dissolved s o l i d s content i n the spent ac id again due t o the high concent ra t ion of s i l i c a t e . HC1 was next , then formic, and l a s t l y a c e t i c acid. seemed t o d i s s o l v e more ma te r i a l a t 175°C than a t 225°C.

This t i m e t h e formic and a c e t i c ac ids both

8 . 2 . 5 ROOSEVELT HOT SPRINGS - FORMATION MATERIAL

F igure 8 and Table 8 $how t h e r e s u l t s of t he acid r e a c t i o n wi th the Roosevelt Hot Springs formation ma te r i a l . Again, t he HF acid d isso lved r e l a t i v e l y much l a r g e r amounts of ma te r i a l than the o the r ac ids . These d a t a a l s o seem t o i n d i c a t e t h a t n e i t h e r the a c e t i c nor formic ac ids w i l l work as wel l with the Roosevelt Hot Springs formation ma te r i a l a s with the Desert Peak ma te r i a l .

--

8.2.6 SIGNXFXCANCE OF L I Q U I D ANALYSIS -- Based on these analyses the following ac ids were found t o be b e t t e r than the o t h e r s f o r each mineral t e s t ed :

Calcium Carbonate - a c e t i c ac id , 4% (Higher temperature increases r eac t ion )

Although a c e t i c acid was b e t t e r based on these tests, it should be pointed out t h a t H C 1 was not run. Based on t he known reac t ion of H C l wi th CaC03, i t is l i k e l y t h a t it would be prefer red over a c e t i c acid.

Kaolin - formic acid, 15% ‘(her temperature r e t a r d s r eac t ion )

Formic acid was found to be very good a t d i s so lv ing t h i s c l a y ma te r i a l due t o leaching l a r g e amounts of aluminum and s i l i c a . It should be kept i n mind t h a t t h e organic a c i d s did leave in so lub le p r e c i p i t a t e s a f t e r r eac t ing .

S e p i o l i t e - HF, 8% a t lower temperature 2% a t h igher temperature

S e p i o l i t e i s usua l ly found i n t h e mud f i l t e r cake l e f t from d r i l l i n g the w e l l . S ince t h i s i s normally j u s t on the formation face ( i d e a l l y with only s l i g h t pene t r a t ion i n t o the formation) , a small HF t reatment would probably be adequate t o s u f f i c i e n t l y d i s s o l v e i t .

Desert Peak Formation - HF, 8% I_

(Higher temperature inc reases r eac t ion )

ci

Roosevelt Hot Springs Formation - HF, 8% - (Higher temperature increases r eac t ion )

Although both these formation ma te r i a l s were dissolved by HF ac id , t he problem

be the acid of choice s ince i t t h e o r e t i c a l l y would not form a s many secondary depos i t s .

Another method of showing the d i s so lv ing power of the ac ids i s shown i n Table - 9 with Desert Peak'and Roosevelt Hot Springs formation mater ia l s . This t a b l e shows t h e pounds of formation ma te r i a l t h a t t h e o r e t i c a l l y would be d isso lved by 1,000 ga l lons of t h e acid t o g ive t h e c a t i o n concentrat ions shown i n the preceding t ab le s . t he c a t i o n s (i.e., CaO, MgO, Na20, SiOZ, A1203, Fe203). Tk-is method does not change the r e l a t i v e rankings of t h e ac ids but i s intended t o show i n everyday terms ( lb / l000 g a l ac id ) t h e d isso lv ing power of t he ac ids .

Another cons ide ra t ion t o be discussed is t he f a c t t h a t some ac ids s e l e c t i v e l y leach p a r t i c u l a r ions. Leaving the o t h e r m a t e r i a l s behind. This could r e s u l t i n the movement of t hese ma te r i a l s and poss ib l e plugging of the formation. s e l e c t i v e l y d i s s o l v e the calcium more than any o the r ion. d i sso lved a l l of them i n s i g n i f i c a n t amounts a t one time o r another , bu t as pointed out i n Sec t ion 8.2.3 did seem t o p re fe r aluminum.

o f secondary depos i t s should always be considered. And here again, H C l could ,- 6

- c This poundage was based on disso lv ing the oxides of each of

i2

This i s e s p e c i a l l y t r u e f o r HF which d i s so lves s i l i c a ,

Acetic acid seemed t o The formic acid P

Y

8.3 ANALYSIS OF SOLIDS FROM COOLED LIQUID - ___I

REACTION PRODUCTS /

Table ,lo shows the ana lys i s of the s o l i d s p rec ip i t a t ed from the f i l t e r e d l i q u i d r e a c t i o n products. three-arm r e a c t i o n v e s s e l i n t o a beaker, then f i l t e r e d through an 0.5 micron f i l t e r . Selected samples o f t hese f i l t e r e d s o l i d s were examined by the e l e c t r o n microprobe f o r i d e n t i f i c a t i o n . These results a r e l i s t e d i n Table 10. It was found t h a t a l l t he ac ids produced these secondary depos i t s but no p r e c i s e i d e n t i f i c a t i o n could be made due to the presence of t h e degradat ion products o f t h e t e s t c a l l i t s e l f ( i . e . , Co, N i , Mo, Fe, and perhaps SiOZ). T a b l e ' l l g ives the amounts of s o l i d s prec ip ta ted from the cooled, f i l t e r e d l i q u i d . The amounts a r e repor ted a s weight percent based on t he t o t a l l i q u i d recovered. Since these s o l i d s were contaminated with the dissolved metal, no at tempt was made to f u r t h e r use. t hese numbers.

oi The l i q u i d was removed from the va lve on the

e --

-- 44

8.4 SCANNING ELECTRON MICROSCOPY

Some samples of t h e Desert Peak formation ma te r i a l s were se l ec t ed f o r SEM examination before and a f t e r acid reac t ion . are shown i n F igures 9 through 15.

Figure 9 shows a p iece of un t rea ted Desert Peak formation ma te r i a l , shows a s i m i l a r p iece t r ea t ed a t 17S°C with 4% a c e t i c acid a t the same magnif icat ion. has reacted with i t . However, Figure 11 a t higher magnif icat ion shows a

Micrographs of t hese examinations - - Figure 10

CI The t r e a t e d sample has a smoother sur face ind ica t ing the acid

G -13-

t

c r y s t a l res idue covering these pieces .

A microprobe a n a l y s i s of these secondary depos i t s showed i t s c a t i o n content t o be almost e n t i r e l y composed of calcium. p r e c i p i t a t e could pose a se r ious problem i f i t i s formed and l e f t i n t he format ion.

Figure 1 2 shows a f r a c t i o n of t he Desert Peak formation containing a c l ay ma te r i a l ( t o p photo). The bottom photo 'shows t h a t 4% a c e t i c acid a t 175°C removes t h e c l a y bbt leaves a coat ing of t he calcium residue.

A d i f f e r e n t type of secondary depos i t is seen on Desert Peak ma te r i a l a f t e r r e a c t i o n with HF a c i d a t 175'C and 225°C (Figures 13 arid 14) . Microprobe ana lyses i n d i c a t e 2% W r e s idue was mainly composed of A l , S i and Ca while t he 8% HF t r e a t e d res idue was only A 1 and K. .

This inso luble calcium-containing v

5

--c

The f i n a l micrographs (F igure 15) show t h e su r face of the Desert Peak formation ma te r i a l a f t e r r e a c t z n with 5 and 15% H C l a t 175°C. was cleaned of any c l a y m a t e r i a l s by the treatment and only a s i l i c e o u s m a t e r i a l was measured by thp microprobe.

9.0 PROBLEMS ASSOCIATED WITH THE ACID TESTS

A major d e v i a t i o n from the labora tory work program (submitted May 5 , 1980) occurred due t o the severe cor ros ion of t h e Hastel loy C r e a c t i o n vesse l s by HC1 a t the proposed t e s t temperatures. This was f i r s t not iced upon running blanks of the a c i d s i n the test c e l l s (Table 3) . Fe and o the r c a t i o n s show up i n t h e ana lys i s . would lead t o a g r e a t dea l of doubt on any analyses run on HC1 r e a c t i o n products due t o the poss ib l e i n t e r f e r e n c e of these c a t i o n s with the

The su r face

----

Large amounts of N i , Mo, A l , -- These d i s s o l u t i o n products

minera l /ac id reac t ions . ope ra t ions , i t was decided t o run two tests with HC1 a f t e r t h e o the r t e s t s were completed. These were run with the Desert Peak ma te r i a l and a r e shown i n F igures 7 and 2. Soon a f t e r t hese tests were run, two of t he Has te l loy C va lves f a i l e d and could not be repa i red . No more t e s t s were run with HC1 i n Has te l loy C due t o concern f o r t h e danger involved i n the poss ib l e f a i l u r e of t h e c e l l s or f i t t i n g s .

It was f e l t t h a t a l l poss ib l e avenues should be explored t o a t t e m p t t o o b t a i n HC1 da ta . ordered. However, a f t e r ob ta in ing the ma te r i a l i t was found t h a t adequate s e a l s could not be machined and at tempts to use zirconium were abandoned.

Also, due t o t h e cor ros ion experienced on the Hastel loy C c e l l s and t h e f a i l u r e t o make adequate c e l l s from zirconium, no at tempts were made t o t e s t t h e ac ids under dynamic condi t ions due t o t h e danger t h a t might be encountered i f t he tubing o r pressure s e a l s would f a i l

However, due t o the importance of HC1 i n ac id i z ing

9

6 To t h i s end some zirconium b a r s tock ( a s Z i r ca l loy 702) was This a l l o y was found t o be impervious t o HC1 a t high temperatues.

6

10.0 RECOMMENDATIONS FOR FUTURE A C I D I Z I N G WORK - - a The major t h r u s t of any f u t u r e work should be t o find adequate m a t e r i a l s t o

cons t ruc t t e s t v e s s e l s t h a t a r e impervious t o ac ids a & these high

F . -1

temperatures. The test procedure i t s e l f and the three-arm tes t ves se l were found t o be very workable. The d i f f i c u l t i e s came i n modifying these t o accommodate t h e d i s s o l u t i o n of the metal and t h e r e s u l t i n g dangers of handling a c i d s a t high temperatures.

I f t h e materials of cons t ruc t ion problem can be solved, then attempts should be made t o flow t h e ac ids through cores. This i s t h e only way t h a t adequate information can be obtained on p o t e n t i a l plugging problems.

11.0 SCALE INHIBITORS - Frequently, scale i n h i b i t o r s are used t o prevent t he formation of downhole scales. For example, a f t e r a w e l l has been acidized, i n h i b i t o r s can be added t o prevent t he formation of scale i n t h e fu ture . A t o t h e r times, i n h i b i t o r s are used as a preventa t ive measure instead o f per iodic a c i d k i n g . done, f o r example, i f scale forming condi t ions are an t i c ipa t ed once a w e l l i s put i n t o production.

This i s

. 11.1 MAJOR SCALING COMPOUNDS - Common scales encountered t h e geothermal industry include but a re not l imi t ed t o calcium carbonate, calcium s u l f a t e , and barium s u l f a t e . Of these scales, calcium carbonate i s probably t h e most troublesome because o f i t s tendency t o form when calcium r i c h b r i n e s containing dissolved carbon dioxide are produced from t he r e se rvo i r . Brines low i n t o t a l dissolved s o l i d s ( i . e . , less than 50,000 ppm) are i n general more prone t o calcium carbonate depos i t ion upon f l a sh ing of carbon dioxide than a r e t h e b r i n e s high i n t o t a l dissolved s o l i d s . For t h i s reason, t h e emphasis i n t h e present work was on calcium carbonate scale i n h i b i t o r s .

11.2 POTENTIAL INHIBITORS FOR CALCIUM - CARBONATE SCALE

-*

A l a r g e number of s c a l e i n h i b i t o r s a re commercially ava i l ab le . Research has i n t h e pas t worked with t h e major manufacturers of t hese chemicals and as a r e s u l t has c o l l e c t e d information r e l evan t t o t h e i r r e l a t i v e e f f ec t iveness for preventing t h e formation o f var ious scales under a v a r i e t y o f condi t ions, Based upon our past experience, t h e following i n h i b i t o r s were considered t o be t h e e i g h t b e s t candidates f o r i n h i b i t i n g t h e foruiation of calcium carbonate:

Vetter

MANUFACTURER I N H I B I T O R

Mons a n t o Dequest 2000; 2010; 2060 Magna HEP 720 T e x t i l ana FOS-A-7561 C T r e t o l i t e SP-245; 252; 267

The major concerns of any i n h i b i t o r t o be used i n t h e geothermal indus t ry are t h r e e fo Id :

1. The hydrothermal s t a b i l i t y of t he i n h i b i t o r under r e s e r v o i r

-15-

0

0

u

i d

v

condi t ions.

The e f f i c i e n c y under the condi t ions which i t is t o be appl ied.

The tendency of the i n h i b i t o r t o form a s c a l e with the r e s e m i o r b r i n e ( i . e . , chemical compatabi l i ty) .

2 .

3 .

Since t h e r e was l i t t l e emphasis on w e l l s t imula t ion by f i e l d ac id iz ing over t h e course of t h e Well St imulat ion c o n t r a c t , more emphasis w a s placed on the f i r s t c r i t e r i a ( i .e . , hydrothermal s t a b i l i t y ) than the o the r t w o c r i t e r i a . I f t h e i n h i b i t o r i s not s t a b l e (i.e., decomposes) a t e levated temperature, i t s e f f i c i e n c y and compatabi l i ty with b r i n e under r e s e r v o i r condi t ions i s somewhat academic. I n add i t ion , i n the absence of a s p e c i f i c r e s e r v o i r t o be ac id ized , d e f i n i t i v e information regarding b r ine composition, formation type, temperature, etc., i s lacking. labora tory .

Experimental design i s impossible i n the

11.3 HYDROTHERMAL STABILITY

The p o t e n t i a l i n h i b i t o r s l i s t e d above were d i l u t e d with a 7000 ppm sodium c h l o r i d e s o l u t i o n t o g ive a f i n a l s tock s o l u t i o n t h a t contained 10,000 ppm of t he i n h i b i t o r s . These s tock so lu t ions were heated a t 500°F f o r varying l eng ths of t i m e and under seve ra l d i f f e r e n t condi t ions. Degradation of the i n h i b i t o r s was monitored by comparing the e f f i c i ency of t he heated s tock s o l u t i o n t o t h a t of the unheated so lu t ion . a b i l i t y of t h e i n h i b i t o r t o prevent t he p r e c i p i t a t i o n o f , i n t h i s case , calcium carbonate i n a sodium ch lo r ide s o l u t i o n a t room temperature. following equat ion is used f o r the c a l c u l a t i o n of t h i s value:

The e f f i c i ency i s a measure of the

The

(I) - (Fs) ( I ) - (Fb) E m 1- -_---_-__-- x 100

e (I)

(Fs) is t h e f i n a l calcium ion concent ra t ion i n a

i s t h e i n i t i a l calcium ion concent ra t ion

s o l u t i o n containing the i n h i b i t o r

(Fb) i s the f i n a l calcium ion concent ra t ion i n a s o l u t i o n - not containing t h e i n h i b i t o r ( i * e s , blank)

M

It i s important t o keep i n mind t h a t t hese e f f i c i e n c y measurements were used on ly t o monitor t h e r e l a t i v e thermal s t a b i l i t y of t h e i n h i b i t o r s evaluated. The a c t u a l e f f i c i e n c y under geothermal condi t ions may be l a r g e r o r smaller than the e f f i c i e n c y measured a t room temperature. The a c t u a l e f f i c i e n c y i s measured once the s p e c i f i c condi t ions hav.e been def ined.

&

I

11.3.1 HYDROTHERMAL STABILITY OF THE "AS RECEIVED" --- INHIBITOR

Stock s o l u t i o n s of each i n h i b i t o r were heated f o r periods of two and s i x hours

s tock s o l u t i o n containing 10,000 ppm of the "as received" i n h i b i t o r , and t h e r e s u l t i n g e f f i c i e n c y are summarized i n -- Table 12. wi th the exception of SP-245, a l l i n h i b i t o r s a r e degraded wi th in two hours t o t h e ex ten t t h a t they no longer i n h i b i t t he formation of calcium carbonate.

I n order t o determine f a c t o r s inf luencing i n h i b i t o r s t a b i l i t y , t he pH o f each s tock s o l u t i o n of t he "as received" i n h i b i t o r was measured. This measurement ind ica ted t h a t all so lu t ions , with the except ion of SP-245, were a c i d i c ( i . e . , had a pH of 2.2 o r l e s s - Table 12). The stock so lu t ion of SP-245 had a pH which was much more n e u t r a m e y pH of 7.86). From t h i s , i t appears t h a t t h e s t a b i l i t y of t h e i n h i b i t o r s a r e pH dependent with more a c i d i c s o l u t i o n s being l e s s s t a b l e than the neu t r a l ones.

U i n an i n e r t (n i t rogen) atmosphere. The i n h i b i t o r s , the i n i t i a l pH of t he

The r e s u l t s i n d i c a t e t h a t

Y

4d

11.3.2 HYDROTHERMAL STABILITY OF THE NEUTRALIZED -- INHIBITOR .

To t e s t t h i s hypothesis , a s tock s o l u t i o n o f t he i n h i b i t o r showing t h e h ighes t i n i t i a l e f f i c i e n c y ( i . e . , Dequest 2060) was adjusted t o a neu t ra l pH of 7.8 by adding sodium hydroxide t o the s tock so lu t ion . were f i r s t degassed by n i t rogen t o remove dissolved oxygen and then degassed and pressur ized with carbon dioxide. t h e atmosphere t h a t t h e i n h i b i t o r would most l i k e l y encounter when appl ied i n t h e f i e l d . The n e t e f f e c t o n . t h e pH due t o dissolved carbon d ioxide i s t o lower it t o approximately 4.5. A s tock s o l u t i o n of SP-245 was t r e a t e d i n a similar fashion. 7.86 (Table 121, t h e pH adjustment s t e p with sodium hydroxide was omitted. This neu t r a l i zed s tock s o l u t i o n was then heated a s before t o 500°F f o r per iods o f two and s i x hours followed by e f f i c i ency measurements t o t e s t the s t a b i l i t y . Table 13 gives the e f f i c i ency of each s o l u t i o n t r ea t ed i n t h i s way. t h e e f f i c i e n c y measurements, t h e hydrothermal s t a b i l i t y of Dequest 2060 i s d rama t i ca l ly improved i n t h e neu t r a l i zed s tock so lu t ion . The a c i d i c s tock s o l u t i o n of t h e "as received" Dequest 2060 d e t e r i o r a t e d so r ap id ly upon hea t ing t h a t even a f t e r two hours , e f f i c i ency was l o s t . The same s o l u t i o n a f t e r n e u t r a l i z a t i o n and s a t u r a t i n g with carbon d ioxide had e f f i c i e n c i e s of 69% and 63% a f t e r two and s i x hours of hea t ing , respec t ive ly . i n h i b i t o r t e s t e d , SP-245, showed e s s e n t i a l l y t h e same behavior a s be fo re when heated i n the carbon d ioxide atmosphere.

4d The so lu t ions t o be heated

The carbon dioxide was added t o s imula te

44 Because the s tock s o l u t i o n of SP-245 o r i g i n a l l y had a pH of --

Q Based on --

* The o t h e r

11.4 RECOMMENDATIONS I N APPLYING INHIBITORS - Isr It i s obvious from the above t h a t t he i n h i b i t o r s a r e thermally less s t a b l e i n t h e "as received" form e s p e c i a l l y i f t he "as received" s o l u t i o n s a r e a c i d i c . While the re may be s u f f i c i e n t d i l u t i o n and/or n e u t r a l i z a t i o n when appl ied i n t h e f i e l d , i f a t a l l poss ib l e they should be appl ied a f t e r n e u t r a l i z a t i o n of t h e "as received" i n h i b i t o r i f t h i s ma te r i a l has an a c i d i c pH. I f i n h i b i t o r

a

* a d d i t i o n i s t o be done i n conjunct ion with ac id i za t ion , t he job should be 41

designed such that exposure of the inh ib i tor to an ac id ic pH a t high temperatures for prolonged periods of t i m e i s avoided.

Y

,

Y

TABLE 1

MATRIX FOR STATIC ACIDIZING TESTS 3 -- - --

MINERALS ACIDS - CaC03 HCL ( 5 and 20x1

Kaolin HF (2 and 8%)

Sepiolite Acetic (4 and 20%)

Desert Peak Formation Formic (2 and 15%)

w I

TEMPERATURES

175 O C

225°C

CI c 47 t c c c" @.

TABLE 2

ANALYSIS OF ACIDS USED IN HIGH TEMPERATURE ACIDIZING TESTS

ION IN SOLUTION

Si02 Fe Cr Mo Ni Mn A1 Na Ca Mg

Hydrochloric Acid 5% ~0.2 ~0.012 ~0,036 0.135 0.398 <0.011 ~0.08 c0.035 c0.001 c0.026 20% ~0.2 ~0.012 ~0.036 0.178 0.872 0.244 ~ 0 . 0 8 c0.035 0.029 c0.026

2% <0.2 0,328 0.055 0.733 0.345 <0.011 cu.08 ~0.035 ~ 0 . 0 0 8 0.404 8% C O . 2 0.451 0.255 2.854 0.972 ~0.011 ~0.08 <0.035 0.013 1.95\

Acetic Acid 4% 3.3 ~0.012 ~0.036 <0.02 ~0.003 ~0.011 c0.08 c0.035 <0.001 c0.026 20% 54.5 c0.012 c0.036 <0.02 0.199 ~0,011 <0.08 <0.035 <0.001 c0.026

Formic Acid 2% 1.77 ~0.012 c0.036 c0.02 0,015 ~0.011 ~0.08 <0.035 c0.001 ~0.026 15% 12.8 c0.012 c0.036 <0.02 0.068 ~0.011 <0.08 <0.035 c0.001 (0.026

I h)

0 Hydrofluoric Acid I

---

Values expressed in mB/l

,.

TABLE 3

ANALYSIS OF ACID REACTION WITH BLANK TEST CELLS AT 225OC FOR 16 HOURS

HASTELLOY C Cr - Fe - S io2 - Na Ca Mg - Element

HC1, 5% 213 27 27 1'13 6534 20,000 20% 68 6 139 ' 92 265 11413 20,000

HF, 2% 705 3.0 1.8 866 286 - 8% 659 13 4.1 5584 858 -

- 2.74 0.28

0.07 15.9 29 .O

0.29 - 0.31 5.2 1.24 1.6 0.69 1.78 36.2 58.2

I Acetic, 4% 2.8 0.14 - w 20% 2.4 - h)

I Formic, 2% -

15% -

HASTELLOY 3 HC1, 5% 346- 1242 1890 416 7930 NR

20% 497 1050 1470 151 8870 83 HF, 2% 1388 36 31 20,900 2470 NR

8% 2312 36 24 29,200 4310 21

Values expressed as mg/l

NR = Not Run

A1

214 17,000 423 2423

4826 22,000 730 4619 18 122 54 1358

- Mn - Ni - Mo -

186 - 1193 - 3 7.51 0.10 -

0.12 93.8 1.67' - - 18.5 0.47 -

1.06 17.6 16.2 0.65

NR 17,000 NR 4590

28,000 22,000 60 4780 NR 7,500 NR 405 4700 8,500 35 2190

Q

3

TABLE 4 -- ANALYSIS OF IONS DISSOLVED FROM CaC03 BY --

ACETIC AND FORMIC ACIDS ---

Si02 - 238 187

642 815

905 1330

2076 4432

Fe - - Na k

4% 57 21 20% 14 ' 28

, Acetic Acid, 175OC Y

2498 2496

< 1 tl

52 98

Acetic Acid, 225'C 4% 69 20% . - w 66

89 5647 4961

15 7 0 5

12.5 32

Formic Acid, 175OC 2% 24 0 1373 ! 15%' 370 4833

'* .Formic Acid, 225OC

2% 170 2759 15% 530 647 1

Values expressed in mg/l

-

703 1056

438 1828

71 44 1

w 543 714

321 916

55 367

v

9

(I

W

TABLE 5

ACETXCTF-IC ---- AND HF A C X

- ANALYSIS OF IONS DISSOLVED FROM KAOLIN BY -

Fe - A1 - Na - Mg - Ca - Si02 - Acetic Acid, 175OC

e. 1 23 81

187 158 c 1 4% 158

20% 232 50 1,382 571 271

Acetic Acid, 225°C

119 345 < 1 146 4% 216 10 237 976 <1 97 20% 24 9 45

Formic Acid, 175°C 2% 118 7.3 10 2060 305 136

15% 1385 52 110 30674 10011 113

Formic Acid, 225OC

97 95

2% 223 5.5 27 1997 2 74 15Z 627 47 464 19476 947 G

. HF, 175OC - - 2% . - - 35.5 20967

8% - - 47.3 24822

u 2% - - 67 23976

- - HF, 225°C

- - - 68 27421 - - 8% - Values expressed in mg/l

Y

rii

*

i

-23- w

u

TABLE 6 -- ANALYSIS OF IONS DISSOLVED FROM

SEPIOLITE BY ACETIC, FORMIC AND HF ACIDS

Acetic Acid, 175OC 4%

20%

Acetic Acid, 225OC 4x

20%

Formic Acid, 175°C 2%

15%

Na - Ca - Si02 - A1 - Fe - 66 85 134 332 <1 *1

132 877 75 1 396 $1 56

I

7 1 33 61 476 5.5 22 140 479 75 593 6.7 74

101 44 2246 326 44 83 6 4 70 2688 337 99 284

29 84

6

TABLE 7 --

w

e

ANALYSIS OF IONS DISSOLVED FROM DESERT PEAK FORMATION BY ACETIC, FORMIC, HF, AND HCl ACIDS

/

Acetic Acid, 175OC 4%

20% ,

Acetic Acid, 225OC 4%

20%

. Formic Acid, 175OC 2x

15%

Formic Acid, 225°C 2%

15%

.HF, 175°C 2% 8%

HF, 225°C 2% 8%

, 175Oc 4?

Ca 3s - Na - 56 47 1228 6 4 591 6383

.. I 11.8 24 - 11.8 47

116 390 4019 117 733 5674

1348 24 28 1962 36 34

343 1879 1229 497 1454 1040

Si02 - 103 319

189 203

284 473

3 90 177

3783 20,804

5,910 29,078

414 154

A1 - 2.6 2.6

- -

- 166

- -

414 400

- 2128

4610 4728

Fe - < 1

673

- -

46 1 1442

- -

638 2482

- 4255

7920 8865

TABLE 8 -- ANALYSIS OF IONS DISSOLVED FROM ROOSEVELT HOT SPRINGS

FORMATION BY ACETIC,, FORMIC AND HF ACIDS ej

Si04 - A1 - Fe - Ca - Acetic'Acid,

4% 20%

175OC

225 'C

186 - - 17 94 6 579

307 3 66

12 - 83

Acetic Acid, 4%

20% 177 355

Formic Acid, 2%

15%

175OC 130 85 1

57 - 129 213

697 7 80

437 425

- 95 .

225 "C Formic Acid, 2%

15% 284 43 7

HF, 175°C 2% 8%

6 HF, 225°C

2%

229 1 19,760

- 5 , 674 29,078 - - 36

TABLE 9

DESERT PEAK ROOSEVELT HOT SPRINGS - -- ACETIC ACID, 175°C

4% 20%

16.1 , 91.5

15.4 10.7

ACETIC ACID, 225°C 4%

20% . 1.96

2.33 1.4 2.9

FORMIC ACID, 175°C 2%

15% 59.8 98.6

13.6 27.9

FORMIC A C I D , 225°C 2%

. 15% 3.16 1.43

2.3 3.5

HF, 175OC 2% 8%

59.7 225.6

18.6 160.1

W, 225°C 2% - 47.9

317.9

208.5 213.0

46.0 235.9 8%

H C l , 175°C 5%

15% e

NR NR

G

G

TABLE 10 -- X-RAY ANALYSIS OF SOLIDS FROM LIQUID REACTIOM PRODUCTS

(LISTED IN DESCENDING ORDER OF CONCENTRATION)

CaCO3 - 17SOC ' --- Acetic - Fe, Ca, C1, Ni, Cr, K Formic - C1, Cr, Ni , Ca, Mo, Fe HF - C1, Mo, Ni, Cr, W, Fe

Kaolin - 175OC Acetic - C1, Ni, Si, Al, Cr, Fe, co Formic - Si, Al, C1, Mo, Cr, K, Fe HF - S i , At, Cr, C1, Mo, K, Ni, Fe

Sepiolite - 175OC Acetic - Si, C1, Cr, Mg, AI, Ni, Mo, K, Ca, Fe, CU

. Formic - Si, Cr, Mu, Cl, Ni, Mg, AI, K, Cas Fe, CU

G

TABLE 1 1

CONCENTRATION OF SOLIDS PRECIPITATED FROM FILTERED L I ~ U I D REACTION PRODUCTS-

, CaC03 -

-1 75OC -225OC

-225°C

Acetic Acid Formic Acid HF 2% 4% 2% a x 15% - - - - - 20% - -

0.07 1.79 0.6 0.05 NR NR 0.07 1.79 v.6 0.05 NR NR

1.22 0.0 0.11 0.11 0.34 0.08 0.16 0.77 263 0.81 0.01 0.29

S e p i o l i t e -175°C 0.42 0.77 0.05 0.05 0 1.33 -225OC 0.47 0.19 0.04 0.08 0.32 0.28

6 Desert Peak

-1 75OC 0.03 0.03 0.09 0.92 0.02 0.04 -225OC 0.11 1.12 0.09 0.05 0.04 0.18

T. BLE 12

HYDROTHERMAL STABILITY OF "AS RECEIVED" INHIBITORS* -- EFFICIENCY (XI**

INHIBITOR 0 HOURS 2 H O U R F 6 HOURS

DEQUEST 2000 1.81 36 0 0

DEQUEST 2010 1 .88 22 0 0

DEQUEST 2060 1 .71 85 0 0

SP 245 7 .86 4 9 4 5 4 3

SP 252 2 . 1 8 41 0

SP 267 1 . 5 5 55 0

FOS-A-7561C 1 .85 24 0

MEP 720 1 . 7 4 19 7

-30-

time.

TABLE 13

HYDROTHERMAL STABILITY OF NEUTRALIZED* INHIBITOR S O L ~ O N S

,

INHZB ITOR EFFICIENCY (%I** -

0 HOURS 2 HOURS 6 HOURS

SP-245 52 43 42

DEQUEST 2060 80 69 63 . . *After heating a neutral solution of the inhibitor in a

carbon dioxide atmosphere at 500°F for the specified period of time.

**Efficiency measured using 20 ppm of inhibitor to inhibit calcium carbonate precipitation in excess sodium bicarbonate (24 hour reading).

-31-

G

e G \

G c -32-

(v

X

X

c3

I

-33-

I W 6 I

c, e, c

HIGH TEMPERATURE WEN

c,

I

b

E

G

FIGURE 4

CALCIUM CARBONflTE [ON CONCENTRATION RFTER ACID RIXCTION

14

12 7 0 0

X 0 - 2 10 E

2

I I I L- 5 K) 15 20

. FIGURE 5

KAOLIN ION ANALYSIS AFTER ACID REACTION

G

6ld

b

G

60

50

40

,

P /

/ /

/

K I D CONCENTRATIW &tog J -36-

Ed

6

6

X

w =?.

E k

FIGURE 6

ION CONCENTRATfON AFTER RCfO REACTlUN

3

2

21

I:

IC

5

flF ACID -K 225°C

ACID CONCENTRRTlONfwt % 1 -37-

FIGURE 7

DESERT PEAK ION CONCENTRATION AFTER ACID REACTION

3

3(

2!

2c

15

10

5

I

225OC HF ACID 175’C

,

I

0 ~ /

I

0 ~ /

0. 0

0 0

I

/ 0

0 I

1EoC

ACETIC ACID

AClO

0

4 0

- H FORMIC AND ACETICACfD ;!25’,

-I

5 IO 15 20

FIGURE 8

ROOSEUELT HOT SPRINGS ION ANALYSIS AFTER K I D REHCTION

3r

25

20

15

?

51 w I

- e - -

Y

flC(0 CONCENTRATION f w t % l -39-

FIGURE 9

SCANNING ELECTRON MICROGRAPH DESERT PEAK FORMATION - UNTREATED

r

V

W

Y

m -40-

FIGURE 10

SCANNING ELECTRON MICROGRAPH DESERT PEAK FORMATION - 4% ACETIC ACID, 175OC

e

3

(u

G

w

FIGURE 11

SCANNING ELECTRON MICROGRAPH

SECONDARY DEPOSIT DESERT PEAK FORMATION - 4% ACETIC ACID, 175OC

FIGURE 12

SCANNING ELECTRON MICROGRAPH DESERT PEAK FORMATION

UNTREATED

4% ACETIC ACID, 175OC

-43-

FIGURE 13

SCANNING ELECTRON MICROGRAPH DESERT PEAK FORMATION 2% HYDROFLUORIC ACID

' 175'C

225'C

-44- .

U

FIGURE 14

SCANNING ELETRON MICROGRAPH DESERT PEAK FORMATION 8% HYDROFLUORIC ACID

Y

FIGURE 15

SCANNING ELECTRON M I C R O G W H DESERT PEAK FORMATION

r- Y

e

5

/

5% HYDROCHLORIC ACID, 175OC

e 15% HYDROCHLORIC ACID, 175OC

-46-

ct ,