SPE/IADC SPEIIADC 18618

Effects of C02 Attack on Cement in High-Temperature Applications by J.e. Shen, Unocal Science & Technology Div., and D.S. Pye, Unocal Geothermal Div.

SPE Members

Copyright 1989, SPE/IADC Drilling Conference

This paper was prepared for presentation at the 1989 SPE/IADC Drilling Conference held in New Orleans, Louisiana, February 28-March 3, 1989.

This paper was selected for presentation by a SPEIIADC Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the International Association of Drilling Contractors or the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of SPE or the IADC, its officers, or members. Papers presented at SPEIIADC meetings are subject to publication review by Editorial Committees of SPE and the IADC. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Write Publications Manager, SPE, P.O. Box 833836, Richardson, TX 75083-3836. Telex, 730989 SPEDAL.

ABSTRACT

Well cement carbonation by COZ containing gas or brine can happen to COZ flooded oil fields, gas fields and geothermal fields. Due to the Unocal's interests in these applications, especially in the high temperature geothermal wells, a field and laboratory testing program was conducted to examine the effects of COZ gas on high temperature cement.

Wellhead cement samples from geothermal wells in the Brawley and Geysers fields were collected and analyzed for carbonation. The degree of cement carbonation was found to be dependent on factors such as, temperature, COZ content in the fluid and location. Both the carbonated and the uncarbonated cement have developed extensive fractures and fine fissures in the matrix due to thermal cycles. The carbonated cement has an acceptable level of compressive strength, but its permeability is normally higher than desired.

Preliminary results from laboratory cement carbonation tests under simulated downhole high temperature, high pressure conditions are presented. A new analytical technique was used to measure the depth of carbonation. The COZ diffusion coefficient in the cement solid matrix was estimated with this technique.

By comparing field, lab and published data, the carbo­nation mechanism in high temperature cement is found to be a function of several parameters, i.e., temperature, COZ content in the fluid and cement additives.

INTRODUCTION

In geothermal well cementing, the need of a high strength and durable cement for high temperature downhole applications (400 to 700°F, ZOO to 370°C) has promoted the practice of addi~g fine silica flour in high percentages into cement. The set cement formed by these additions has proved to be temperature stable

Reference and illustrations at end of paper

19

over long period2 and also satisfied the API recom­mended criteria.

3 However, a recent report shows that several geo-thermal well casings in the Broadlands field, New Zealand, failed from the exterior and ruptured. There was little cement remaining around the casings. The corrosion of both cement and casing was attri­buted to the pres~n§e60f high COZ containing fluids. Milestone, et al ' , , also report that severe attack by COZ-Rich fluid occurred within several months for cements meeting API recommendations for strength and permeability.

To evaluate that whether Unocal geothermal wells in the Brawley and Geysers fields have the COZ-induced cement carbonation problem, and whether carbonation affects cement properties, a field cement sampling program from abandoned wells in these two fields was initiated in 1986. A complementary research program was also initiated at Unocal Science & Technology Division in 1987 to understand the mechanism of cement carbonation and also to find out ways to mitigate field problems.

DESCRIPTION OF \vELLS

Eleven wellhead casings were cut off about ZO-30 feet (6-10 meters) from surface from the abandoned Brawley field in the Imperial Valley and sent to Unocal Science & Technology in early June, 1986. All of these wells were abandoned in 1985-1986. Based on the cumulative injection and production poundage, the major production wells and injection wells are listed in TABLE 1 and TABLE Z in descen­ding order.

Cement samples were collected from five wells in the Geysers field, which includes one injection well, one exploratory well and three production wells. Only one production well wellhead was cut off and sampled through the whole casing annuli. The other four wells did not show much evidence of cement carbonation. The typical production temperature of

2 EFFECTS OF CO 2 ATTACK ON CEMENT IN HIGH TEMPERATURE APPLICATIONS

this well was between 354 and 382°F (179 and 194°C) and production pressure between 125 and 240 psi (0.9 and 1.7 MPa). The steam contained about 12200 ppm CO

2,

The typical geothermal casing design includes a surface conductor, a surface casing, an intermediate casing and a production casing. A typical cement slurry for the intermediate casing consists of Class G cement, 40% silica flour with or without light weight additive. A typical cement slurry for the production casing consists of Class G cement, 40% silica flour, 2-3% gel and other additives.

FIELD SAMPLE PREPARATION

The wellheads were cut open by an abrasive saw. Photos were taken to record the appearance of each cement sheath. A number of steel casings were found to be corroded but only to a minor degree.

Cement block samples were taken from the top, the bottom and in most cases the middle locations along the cement sheath length. A duplicate set of samples were also taken from the opposite side of the sheath. Most block samples were picked out of the sheaths rather easily because of the existing fractures.

To maximize the useful information that can be gathered under the allocated budget, a sampling criteria was established so that the most likely carbonated wells would be analyzed first along with some reference samples. Cylindrical core samples of 0.88" (2.24 cm) diameter were drilled out of the cement blocks in the radial direction for the compres­sive strength and water permeability tests. Repre­sentative pieces were collected for the analytical tests.

EXPERIMENTAL

Field Samples

The cement compressive strength was determined by crushing the cylindrical samples of about 1" (2.54 cm) height according to the ASTM C 109 test procedure. Three to six samples were tested for each sample location. Variation of strength measurements for the same location was between 500 to 1000 psi (3.4 MPa to 6.9 MPa).

Similar dimension samples were also prepared and tested for the water permeability according to the API Spec 10-G. Two to three samples were run for each sample location. The permeability value mea­sured reflects the water flow tendency in the sample block which contains fine fissures, but it does not reflect the permeability of the overall cement sheath, because the sheath also contains large fractures.

The carbonate content in the cement was determined by the wet CO 2 evolution technique. Quantitative X-ray diffraction (XRD) was used to determine the crystal­lographic phases and their amounts in the cement. Scanning electron microscopy (SEM) technique was used to reveal the morphology of the cement. One sample was analyzed by the thermal gravimetric analysis (TGA) to check the carbonate content.

20

Three well samples with known CaC03 existence were analyzed by thin section microscopy under polarized light. The thin section plane was parallel to the radial cross-section of each cement sheath. The radial distribution of CaC03 in the three samples were recorded with a special Alizeran Red dye.

Research Samples

The research samples were drilled from cubes cured by cement curing chambers under geothermal tempera­ture and pressure. The 0.88" (2.24 cm) cylindrical cores were then put into autoclave bombs which contained a water reservoir. The samples were situated above the water reservoir by a specially designed sample holder to ensure radial CO2 dif­fusion into the cores. The autoclave bombs were then put in an oven, pressured with CO

2 gas, and

heated to the desired reaction temperaEure.

Most of the analytical tests for research samples were done similar to the methods mentioned above. In order to measure the location of the carbonation layer in some samples, the Electron Probe Micro Analysis (Micro probe) was employed. The probe measures tlle carbon distribution in the cement core as a function of radial distance and has an accuracy of 20%.

RESULTS AND DISCUSSION

Reaction Characteristics

The crystalline nature of Class G cement is depen­dent on temperature. The calcium silicate hydrate (CSH) gel is produced at low temperatures. Under higher temperatures it will convert to other cry­stalline phases. The mechanism of this ,onversion is demonstrated in the following scheme:

CSH 247°F Excess Ca(OH)2 -------> -------------->

> 35% Silica

-------> ---------------> Tobermorite (C5S6H5)

302°F

----> Xonolite (C6S6H)

420-600°F 284-572°F Truscottite <---------------------------> Scawt'te (C7Sl2H3) Active Si0

2 C0

3*2- (C7~6C'HL

Basic Environment

The carbonation mechanism of cement involves the conversion of calcium hydroxide CS(OH)2 and calcium silicate hydrate (CxSHy) to CaC0

3 :

Ca(OH)2 + 2 (H)+ + (C03

)2- ==> CaC03

+ 2 H2

0

2-CxSHy + 2 (H)+ + (x-x') (C03

)

Cx'SHy' + (x-x') CaC03

+ z H2

0

==>

When Ca(OH)2 is carbonated into CaC03

, its molar volume increases from 33.6 to 36.9 cubic centi­meters. Consequently the CaC03 formation from Ca(OH)2 can appreciably reduce the cement perme­ability by volume expansion. Conversely, the

3

SPE 18618 J.C. SHEN & D.S. PYE

reaction of CxSHy with CO results in a highly polymerized silica gel an~ a reduction of solid volume. This increases cement permeability.

Published data have shown that CO2 attacks Ca(OH)2 first if a cement contains that compound. In normal geothermal applications, where 40% silica flour is mixed with Class G cement, the CO2 is likely to attack CxSH~ gegause of the lack of Ca(OH)2 in the set cement. ' ,

Calcium carbonate is polymorphous and exists in at least five modifications. The two commonly found in nature are calcite and aragonite. Aragonite is metastable at low pressures and slowly alters to calcite. Vaterite is also a metastable form which 9 crystallizes at ordinary temperatures and pressures. The transformation of CaC0

3 polymorphs is shown

below:

CO2

<80°F >86°F CxSHy ---> Vaterite ----> Aragonite -----> Calcite

The transformation is a slow and kinetic-limited process.

Visual Observation of Field Samples

After the casings were cut open, the cement showed significant visible fractures. In addition to the visible fractures, most cement sheaths also developed fine fissures extending from exposed surfaces into the cement matrix. Solid deposits were found in both types of fracture. Evidence of brine intrusion into the fine fissures was also abundant, but there was no signs of cement erosion or loss.

Experimental Data of Field Samples

The experimental data from the compressive strength test, the permeability test, the wet CO2 evolution test and the XRD analysis for the Brawley field samples are listed in TABLE 3. The .. s .. symbol in sample names indicates the intermediate casing annulus, the "P" production casing annulus and the "Roo redrill casing annulus. Comparative measurements at the same axial position but on the opposite side are shown as duplicate data. Data shown for Veysey 15 production casing cement includes the two loca­tions at the bottom of the wellhead and one at the top for comparison.

All but the Tow 1 intermediate casing cement have compressive strength above 1000 psi (6.9 MPa). As expected, the intermediate casing cement is weaker than the production casing cement because of the lighter weight. The CaC03 content does not affect compressive strength systematically, see Figure 1. A similar lack of correlation between compressive strength and well in-service time is apparent in Figure 2.

Most samples have permeability above 0.1 millidarcy. Highly fractured samples were also found to be very permeable. Figure 3 shows that there is no good correlation between permeability and CaC0

3 content.

When compressive strength and permeability data of the major production wells (TABLE 1) are plotted

21

against the number of production shutdowns, as shown in Figure 4, significant trends appear. The data indicates that cement started to lose strength and to gain permeability after nine production shutdowns. Cement forms fissures when its tensile strength is less than the thermal tensile stress caused by a sharp temperature drop. As the cement gets more fractured by thermal cycles, both compre­ssive strength and permeability deteriorate.

The amount of CaC03 in the intermediate casing cement of production wells and in the major injec­tion wells is small. But in the production casing cement of major production wells, the CaC0

3 content

ranges from 24 to 48% by weight of cement. Calcium carbonate content derived from quantitative XRD analysis is in fair agreement with the more accu­rate CO2 evolution technique. The TGA analysis of one sample from Veysey 15 production casing cement shows 32.2% CaC01 by weight, which agrees well with CO2 evolution meEhod.

It was found that the amount of CaC03

in the production well production casing cement is direc­tly proportional to the maximum static downhole formation temperature, Figure 5. The data is also listed in TABLE 4.

The rate of carbonation seems to be rather high for the high temperature wells. It took Veysey 9 only 13 days to get 48% CaC0

3.

The solubility of CO 2 in water at high temperature and pressure is calculated and plotted in Figure 6. Values of the Henry's Law coefficient for CO 2 sote­bility in water was taken from Ellis and Golaing • To get CO2 solubility in 75,000 ppm chloride (Cl-) brine near 580°F (304°C), multiptr the solubility from Figure 6 by a factor of 0.5 .

Since the static formation pressure in Brawley wells is between 2000 and 3000 psi (13.4 and 20.7 MPa) , the CO2 solubility increases rather fast in the temperature range under considerations. Along with the kinetic effect of higher temperature in a hot well, the fast carbonation on Veysey 9, which had a static pressure close to 3000 psi (20.7 MPa), is expected.

TABLE 5 lists the XRD analysis data. The large reading of vaterite- the initial carbonation product- in Veysey 9 confirms that the carbonation was rather new, only 13 production days. On the other hand, the longer production wells, such as Tow 1, Veysey 12 and Veysey 15, contain more calcite and aragonite in their cement.

Halite (NaCl) and gypsum (CaS0t.) were found in most samples, which suggests that the formation brine intruded into the annult and deposited these two compounds. The high temperature calcium silicate hydrates-xonotlite and tobermorite- were found in the hot production wells such as Veysey 12 and 15. The redrill cement of Veysey 8 contains quartz and portlandite (Ca(OH)2)' two typical compounds found in a good geothermal cement.

Figure 7 shows a theoretical temperature distri­bution during production in the cement annuli.

4 EFFECTS OF CO~ ATTACK ON CEMENT IN HIGH TEMPERATURE APPLICATIONS SPE 18618 L.

Earlier reports4 ,5,6 have suggested that cement carbonation starts at fluid-accessible surface. With the aid of a special dye, Alizeran Red and polarized light, the results show that it was indeed the case. Carbonated cement layers were found next to the cement-casing interfaces and also next to the cement fractures (Figure 8). The thickness of these layers ranges from 1 to 6 millimeters. Fissures of 100 to 500 micron sizes existed extensively in Veysey 8,lZ and 15 samples and some finer fissures were filled with CaC03 deposits. The demarcation between the carbonated layer and the good cement solid matrix was well defined in some cases and were diffuse in other cases. Higher concentration of CaC03 was found in the inner region close to the production casing. Since the inner region was hotter during production, higher CaC03 amount is expected.

It is not known why the demarcation between carbo­nated and ,uncarbonated layers can be sharp or dif­fuse. But since cement carbonation is a diffusion limited chemical reaction, the temperature of cement might have played an important role.

Figure 9 shows the existence of a CaC03 filled fine fissure in Veysey 15 production casing cement.

There was no cement carbonation found in the produc­tion well in the Geysers field. The well was by far the most likely candidate to witness cement carbo­nation in the five wells tested in the Geysers field. Since the maximum production temperature was less than 400°F (Z04°C) and the CO Z concentration was lower than that in the Brawley field, the potential for CO attack was much less. From Figure 5, it is concluaed that the wells in the Geysers field may not have serious carbonation problem due to the tempera­ture.

Research Samples

Figure 10 shows the carbon concentration distribution of a geothermal cement sample cured under 450°F (Z3Z0C) and 3000 psi (ZO.7 NPa) and carbonated under 450°F (Z3Z0c) and 1500 psi (10.4 NPa) for three days under water. The outer edge of this sample to the left. The carbonatedlayer stopped at 800 microns from the outer edge. Assuming that the carbonation was a diffusion-limited chemical reaction and a shrinking core model was applicable, then the COZ diffusion coefficient in the cement solid matrix is estimated to be about 8.0x10-7 cmZ/sec at the reaZ: tion temperature and pressure. The average (C03 ) content was 16% by weight of cement.

When the geothermal cement was carbonated above water at 400 F (Z04 C) and 1000 psi (6.9 MPa), the mechan­ism of cement carbonation was changed to kinetics­limited. The whole sample was carbonated uniformly, see Figure 11. The four hour carbonated sample contains 3.Z% (C03)Z- by wt of cement. Figure 1Z shows the same cement carbonated for eight hours, it contains 8.9% (C03)Z- by wt of cement.

Based on the preliminary laboratory test can be said that the mechanism of cement can be affected by whether the COZ is in gaseous state or is dissolved in water. being planned to be done in this area.

results, it carbonation a moist More work is

22

CONCLUSIONS

Wellhead cement samples from geothermal wells in the Brawley and Geysersfields were collected and ana­lyzed for carbonation. The degree of cement carbo­nation was found to be dependent on factors such as, temperature, COZ content in the fluid and location. No cement carbonation was found in the Geysers field due to its low production temperature and low COZ concentration.

Both the carbonated and the uncarbonated cement have developed extensive fractures and fine fissures in the matrix due to thermal cycles. The carbonated cement has an acceptable level of compressive strength, but its permeability is normally higher than desired.

Preliminary results from laboratory cement carbo­nation tests under simulated downhole high temper­ature, high pressure conditions are presented. A new analytical technique was used to measure the depth of carbonation. The CO

Z diffusion coefficient

in the cement solid matrix was estimated to be 8.0x10-7 cmZ/sec by this technique.

By comparing field, lab and published data, the carbonation mechanism in high temperature cement is found to be a function of several parameters, i.e., temperature, CO Z content in the fluid and cement additives.

ACKNOWLEDGEMENTS

The authors wish to thank the management of Unocal for permission to publish this article and to gratefully thank all Uno cal personnel who were involved in this project.

REFERENCES

1. J. P. Gallus and D. E. Pyle, "Performance of Oil-Well Cementing Compositions in Geothermal Wells", SPE 7591, presented at the 53rd Annual Fall Meeting of the Society of Petroleum Engineers, 1978.

Z. API/ERDA Task Group, "Cementing of Geothermal Wells", Progress Report No.3, Brookhaven National Laboratory, BNL 506Z1, 1976.

3. J. W. Hedenquest and M. K. Stewart, "Natural COZ-Rich Steam Heated Wate'rs in the Broadlands­Ohaaki Geothermal System, New Zealand: Their Chemistry Distribution and Corrosive Nature", Geothermal Resources Council, International Symposium Energy, Hawaii, August 26-3-, 1985.

4. N. B. Milestone, L. E. Kukacka and N. Carciello, "Effects of Carbon Dioxide Attack on Geothermal Cement Grouts", Geothermal Resources Council, Transactions. Vol 10, pp. 75-79, September, 1986.

5. N. B. Nilestone, T. Sugama, L. E. Kukacka and N. Carciello, "Carbonation of Geothermal Grouts­Part 1: CO2 Attack at 150 C", Cement and Concrete Research, Vol. 16, pp. 941-950, 1986.

SPE 18618 J.C. SPEN & D.S. PYE

6. N. B. Nilestone, T. Sugama, L. E. Kukacka and N. Carciello, "Carbonation of Geothermal Grouts­Part 2: CO2 Attack at 250 C .. , Cement and Concrete Research, Vol. 17, pp. 37-46, 1987.

7. L. H. Eilers, E. B. Nelson and L. K. Moran, "High-Temperature Cement Compositions-Pectolite, Scawtite, Truscottite, or Xonotlite: Which Do You Want?", Journal of Petroleum Technology, pp. 1373-1377, July, 1983.

8. D. D. Onan, "Effects of Supercritical Carbon Dioxide on Well Cements", SPE 12593, Permian Basin Oil & Gas Recovery Conference, Midland, Texas, 1984.

9. W. A. Deer, R. A. Howie and J. Zussman, "An Introduction to the Rock-Forming Minerals", John Wiley and Sons Inc., 1966.

10. A. J. Ellis and R. M. Golding, "The Solubility of Carbon Dioxide above 100 C in Water and in Sodium Chloride Solutions", American Journal of Science, Vol. 261, pp. 47-60, January, 1963.

11. A. J. Ellis and W. A. J. Mahon, "Chemistry and Geothermal Systems", Academic Press, pp. 132, 1977 .

23

5

TABLE 1 Major Production Wells =:::::::;::::::::: == :::=:=::::;::::::;::::: ==:;:::

Production Maximum Cumulative Tota 1 In-Service S ta tic

Name MMLB Days M ~ Time (yr) Temp (F)

Veysey 12 7913 820 5746 Sect on 16 4.0 478 Veysey 15 3517 345 6915 Sect on 16 3.0 493 TABLE 4 Tow I 844 158 5031 Sect on 16 10.5 540 Major Production Well Data Veysey 8 495 103 8077 Sect on 16 7.0 496 Cox I 110 26 9609 Sect on 15 8.5

:::::::;::: =============:;:;====:;:; ===

Veysey 9 59 13 7908 Sect on 16 6.5 557 Cumu. Prod. Number of Maximum Stati c Name Days Shutdown Tempera ture, F CaC03 , wt%

- .. _-- ...... __ .. -------------- ----------Veysey 12 820 9 478 27.6 Veysey 15 245 4 493 33.5

TABLE 2 Tow 1 158 23 540 36.7 Major Injection Wells Veysey 8 103 11 496 31.2 :::::: === ===::: === -:;== =:::===::: Cox I 26 7

Veysey 9 13 3 557 48.3 Injection Maximum

Cumulative Total In-Service Static Name MMLB Days M ~ Time (,F) Temp (F)

Kruger I 7108 767 6793 Section 17 9.8 561 Veysey 8 4772 881 8077 Section 16 7.0 496 Tow 1 3192 466 5031 Section 16 10.5 540

TABLE 5 XRO Analysis

Veysey 2 3110 851 5921 Sect i on 21 10.7 440 ======== ======= ========:::

Veysey 9 1566 450 7908 Section 16 6.5 557 Veysey 1 708 427 5120 Section 15 10.7 414 Name Calc. Arag. Vater. Quartz Halite Xonot. Tober. Other

~ TABLE 3

Experimenta I Data

Tow 1 -p mod min ptr min mod pm;n pmin CaS04 Veysey 1 -p pmin m; n+ min Veysey 8 -S tra min min min min

-S min min mi n/mod pmin min ================= -p mod min min min

XRD Compres s; ve Permeabil i ty CaCO by CO 2 CaCO

Name Strength (psi) (millidarcy) Evor. (wt%) (wtd ------------ -----------

Cox 1 -p 4980 Jimi nez 1 -p 3550 Kruger 1 -S 1730

-p 2330 Slater 1 -p 2764 Tow 1 -S 570

-p 3493 50.3 36.7 27.8 Veysey 1 -S 4660

-P 4729 0.0 1.3 Veysey 2 -p 3035

-p min min min tra mi n/mod t r/mi n

-R ptr mod min Ca(OH)2 -R mod min Ca(OH)2

Veysey 9 -p min mod min pmi n CaSO 4 Veysey 12-P min min min ptr ptr min pmi n CaSO 4

-P min min tra mi n/mod mod pmi n CaSO 4 Veysey 15-S pm;n min min/mod pmin min

-S min mod m;n+ -S min m;n+ min+ -S m; n m; n/mod mod -P mod tra min ptr CaSO 4 -p mi n+ tra min ptr ptr min tra pmi n CaSO 4 -p tra mod+ tra mod CaS04

Veysey 8 -S 2202, 3304 0.98, 0.61 2.8, 2.9 -p 1804, 1877 0.41, 1.91 34.0, 28.3 -R 2202, 3304 0.39, 0.55 1.1, 1.8

Veysey 9 -S 1440 -p 4620 1.19 48.3

Veysey 12 -P 4223, 6859 3.74, 5.73 31.0, 24.2 26.6 22,.5 Veysey 15 -S 2179, 1903 1.01, 1.07 0.6, 0.7 3.3

-p 7039, 4304 1.55, 0.033 33.7, 33.3 30.2 4223, ---- 0.37, --- 3.1, --- 3.2 ---

mod= moderate, min= minor, tr, tra= trace, p= possible. Calc.= Calcite, Arag.= Aragonite, Vater.= Vaterite, Xonot. = Xonot lite, Tober.= Tobermorite.

8000

7000

iii 6000 !!:. :z: I-0 z 5000 w a: I-., w > iii ., w a: ... 2 0 (,)

1000

0 ~ ~ :::; iii <I: w 2 a: w ...

A

A

A

A A

A AA

A A

A A A

10 20 30 40 50 60

CALCIUM CARBONATE CONCENTRATION (WT%)

Figure 1. Concentration of CaCO, (wt %) vefSUS

10MD

9

8

7

6

5MO

4

3

Compr ... ive Str.ngth (pli)

A A

A

10 20 30 40

CALCIUM CARBONATE CONCENTRATION (WT%)

Figure 3. Perm.ability versus Calcium Carbonate Concentration

8000

7000

6000

iii !!:. 5000 : l-0 Z w a: I- 4000 ., w > iii ., w a: ... 3000 2 0 (,)

2000

1000

SO

50

0 40

~

5 iii 30 <I w 2 a: w ...

20

10

A

50

25

SPE 1861 8

SYMBOLSA: CLASS G + 40% SILICA FLOUR 0: CLASS G + 1: 1 PERLITE

+ 40% SILIC~ FLOUR A

A

A A A

A A 0

A

A

AO 0 A

0 £l 0

A

0

2 3 4 5 6 7 8 9 10 11

IN-SERVICE TIME (YR)

Figur.2. Brawley Field Cement Compr.ssive Strength versus In-Service Time

6000

?-, ,,>{ 1 I , I

, " \ l I '-a \ 5000 I \ /

6 \ / \ I / \ / 4000

r --j "",0 \ I"r-\ 3000 \ / \ ","/ \ ",,,,,,, / \ ,

/ 2000 /y"

/ /

/ 1000

~/--1 ~- - A

2 4 6 8 10 12 14 1S 18 20 22 24

NUM8ER OF PRODUCTION SHUTDOWN

Figure 4. Compressive Strength and Permeability versus Number of Production Thermal Cycles

12

iii !!:. :z: I-0 z w a: I-., w ~ ., ., w a: ... ~ 0 (,)

50

~

~ z 50 52 ~ 0:: ... Z ... 40 (J Z 0 (J ... ~ 30 Z 0 III 0:: « (J

" 20 :> U oJ « (J

10

8

7

6

q, 6 :z:

III oJ

~ "-0 4 (J

III oJ

~ iii 3 :> oJ 0 III

2

~

400 420 440 450 480 500 620 540 560 580 600

MAXIMUM STATIC TEMPERATURE (OF)

Figure 6. Calcium Carbonlte Concentration versus Maximum Static Temperature

V~8 TOWl VC12

\ \ b

\

100

'" 0...

200

" ......... __ P=1470 / ----Q---;I

P= 736

/

/

/ /

......... _ P=368 /

-0-"1

300 400 500 600

TEMPERATURE (OF)

Figure 6. Solubility of CO2 in Woter (Totol Preuure in pli)

26

It

t ... 0:: :> ~ 0:: ... ... " ... ...

500

400

300

200

100

500°F GEOTHERMAL FLUID

GCEMENT PLUS 40% SILICA FLOUR

4.8" 6.7" 10.0"

I --' STEEL CASINGS

FORMATION

Figure 7. Clment Temperatur. Diltribution During Production

Fig. 8-Thin-section photo of Veysey 15 production casing cement.

Fig. 9-SEM photo of Veysey 15 production casing cement.

f­Z

60.

I!l ~ 40.0

IT W 0..

f-~ 30.0

H W 3:

20.0

10.0

0.0

20.0

15.0 f-Z

m ~ IT W n.

H W 3:

5.0

0.0

Fig. 10-Carbon distribution 01 a carbonated cement at 1,500 psi and 450°F by Microprobe.

--_._----_ .. _--_._----- .. _-_._--_._.--_._--._----._-_.--_._-_._--- . - - .. _, I i I

I I

I I

I

10000

IN M1CRON~

Fig. II-Carbon distribution at 1,000 psi and 400°F lor 4 hours as measured by Microprobe.

27

20.0,---------------------··--

15. l-Z

I!I W (J a: W a.

H W 3:

5.0

, ' , .

I

111111111111111111111111111111111111111111111111111111111IIIIIII~ 10000

OISTANC~--Hr MICRUNS

Fig. 12-Carbon distribution at 1,000 psi and 400'F for 8 hours as measured by Microprobe.

28