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Reliable casing packer seal elastomers for the unusually severe geothermal environment a t 260°C (500°F) did not e x i s t in 1976. L'Garde, Inc., was awarded a contract to f u l f i l l this need by the United States Department of Energy. Successful developnent was completed in 1979. Compounds based on four d i f f e r e n t polymer systems were developed, a l l of which exceed the contract requirements. Successful laboratory tests above 300'C (575OF) have been performed w i t h packer seals. Field tests to temperatures as high as 317OC (603°F) have been performed on static O-rings in a cablehead, Successful, dynamic, d r i l l bit seal tests w e r e run with a presoak temperature of 288°C (550°F). The successful compounds are based on the following polymer systems: EPDM (Nordela), FKM (Vitona), EPDM/FKM (Nordel@/Viton@) blend, and propylene-TFE (AFL\S@) Evaluation was performed on full-scale packer seals as w e l l as on O-rings by L'Garde. L'Garde ran comparison tests against commercir l l y available elastqmers including Ka Irez@. C a s e histories of other organizations which have laboratory and/or downhole experience with oce or more of the developea compounds are presented. The applications c i t e d include blowout preventors, dynamic d r i l l bit seals, packers,, and cableheads. Finally, an effort to a c t i v e l y transfer t h i s technology t o the industry is described

In late 1976 L'Garde, Inc. was awarded a contract by the United States Department of Energy (DOE) , DEAC03-77-ET28309 (formerly EG-77-\cJ C-03-1308), the Geo-Elastomeric Materials (GEM) Program [1,2] . By that t i m e the DOE concluded that there was a general need for improved elastomers for various s e a l applications which were required to operate i n the unusually severe geotherma1,environment. Logging equipment could not be run for fear of losing seals and damaging the instrumentation. Packers could not be run without first cooling the w e l l . Rotating w e l l head seals and BOP seals required frequent replacement. There was a general need for higher temperature, more hydrochemically and extrvsion r e s i s t a n t elastomers and for that matter the need is still not satisfied i n practice today i n the geothermal field. L'Garde performed an i n i t i a l task to identify what elastomer application when upgraded to geothermal requirements would be of greatest benefit to the geothermal community. The formation packer was identified for t w o functions, hydraulic stimulation and i n t e r v a l t e s t i n g i n support of reservoir and w e l l characterization. However, though high temperature geothermal formation packers are needed, development of elastomers for this application was judged too ambitious a goal for the first e f f o r t . Therefore, it was recommended and approved to first develop improved elastomers for casing packer seal elements. In addition, rubber development for the casing packer element " k i l l s two birds w i t h one stone", as those elastomers which work successfully for the packer seal w i l l m o s t probably work w e l l for static O-ring seals. The O-ring application is-less severe because both surfaces are machined, the clearances are small and the required deformation of the O-ring is small compared to a casing packer seal element, In 1979 a f t e r the completion of the elastomer compound development, L'Garde was awarded a contract to actively t r a n s f e r the developed technology to industry. DOE through Brookhaven National Laboratory under contract BNL 490316-S, Geothermal Elastomeric Materials Technology Transfer, development €or high temperature geothermal casing packer seals, case h i s t o r i e s of laboratory and f i e l d experience by other organizations, and a description of the present technology transfer e f f o r t . 1 The t r a n s f e r is sponsored by the This paper presents the r e s u l t s of the elastomer compound GEOTHERMAL PACKER ELASTOMER COMPOUND DEVELOPMENT The objectives of the elastomer development contract w e r e successfully m e t . Though meeting the fundamental objective, t o de-relop a casing packer seal elastomer compound which w i l l operate i n a 26OOC ( 5 O O O F ) geothermal environment, was highly challenging and carried with it a d e f i n i t e probability of failure, L'Garde was fortunate to be able t o conclude the program with very positive r e s u l t s , 15-2 Packer seals which pe rm w e l l i n the o i l f i e l d up to temperatures of about 15OOC (302OF) run i n t o r e l i a b i l i t y problems (& at higher temperatures especially when they get as high as 260OC. Though the stresses induced i n t o the elastomeric element are subs t a n t i a l l y the same as at the lower temperatures, the loss in elastomer strength at 26OOC is substantial and, typically, the stress exceeds the reduced strength and f a i l u r e occurs. O t h e r common problems include hardening or reversion softening of the elastomer at higher temperatures with associated failure. The geothermal elastomeric packer seal problem at 260°C^'is significant and even the less demanding-static O-ring seal is still a problem. Figure 1 rather lucidly i l l u s t r a t e s the s t a r t i n g point of the geothermal packer seal development. synthetic brine. A t these unusually severe conditions, the seals did one of three things; extruded severely (B3), could not withstand the pack-off and cracked without sealing (220-3), or extruded and broke catastrophically (D3 and E3). For about the first 2/3 of the contract, it was doubtful t h a t elastomer improvements alone would provide reasonable performance at the test conditions at the special tests proved invaluable and enabled e f f i c i e n t evaluation of 129 compounds with quick feedback for subsequent compounding efforts. 96 seal Simulation T e s t s w e r e run which provide data which is closely correlated with operational performance with l i t t l e need for uncertain extrapolation to judge how conpounds w i l l perform operationally. The testing and evaluation scheme ' described below and is detailed i n References 1 and 2. These post mortem test specimens w e r e run at 26OOC i n The 2-phase Screening and Simulation Test evaluation scheme w i t h Screeninq T e s t s -- A battery of si,mple tests w e r e defined for d brush screening of compounds specimens cut from standard test s specimens and specimens aged i n synthetic geothermal brine at 260OC were made to assess the hydrothemochemical stabilkty of the compounds. The synthetic geothermal brine was defined 'and developed specifically for the elastomers development. levels include almost the e n t i r e population of known geothermal resource areas. high levels measured i n some locations which correspond fraction of the population. The synthetic Brine is an aqueous solution of 300 ppm H2S, 1000 ppm C02 and 25,000 ppm NaC1. s t a r t i n g pH is about 5. To specifically address the important problem, extrusion, a special test was designed and fabricated which measured the extrusion resistance of a specimen about the s i z e of a quarter. A good quantitative demonstration of the compounding accomplishments is seen through a comparison of characteristics for early compounds against commensurate ones at the completion of the program. This can be clearly seen by examining the data generated under the Screening Tests. The most pertinent parameters measured are ultimate t e n s i l e strength, ultimate elongation, Shore A hardness, and extrusion resistance. A l l screening tests used simple bs and comparisons between virgin The constituency This constituency s p e c i f i c a l l y avoids The The t e n s i l e and elongation were measured at room 15-3 temperature while the hardness and extrusion resistance were measured a t 26OOC. Table I i l l u s t r a t e s the improvements as indicated by the percent of each of the four critical c h a r a c t e r i s t i c s retained after ageing i n synthetic brine for 22 hours. virgin and chemically aged values.which are represented by the percentage numbers. N o t e t h a t there is s i g n i f i c a n t improvement reflected by the latest compounds. The 267 EPDM is v i r t u a l l y unchanged by the 22 hour ageing i n the s y n t h e t i c b r i n e with respect to a l l four characterizat i o n parameters indicating phenomenal hydrothermochemical s t a b i l i t y i n the synthetic brine. V a s t improvement was f i n a l l y accomplished with the 255 FKM: There is room for improvement on the extrusion . resistance especially, as is reflected by the packer seal Simulation T e s t s , however, the extrusion resistance is adequate to m e e t the requirements and the r e s u l t s are quite respectable. The 266 EPDM/FKM is very stable with some minor degradation of the ultimate elongation. The 291 Propylene-TFE shows some minor hydrothermochemical i n s t a b i l i t y i n the ultimate elongation. In general, a l l of the latest formulations showed very good s t a b i l i t y considering the unusual severity - of environment. ij Table I1 lists the The above data and tests are a l l comprehensively reported i n Reference 1. s -- Those compounds which performed w e l l raduated to full-scale packer seal tests. subjects a f u l l - s c a l e 10.2 cm (4-inch) packer seal to simulated downhole environments, i n the laboratory. In t h i s test the seal is simultaneously s ected to the chemistry, temperature, mechanical . forces, pressure rces, and limited surface exposure of the seal j u s t as it is on spectrum of i n t e tive operational environments, the combination of which is important when evaluating materials being stressed to t h e i r ultimate cap (one was required) separate polymer systems molded i n t o full-scale packer seals successfully sealed i n laboratory packer S I M T e s t s - i n excess of the prescribed duty cycle -- temperature of 26OoC, i n synthetic geothermal brine, d i f f e r e n t i a l pressure of 21.4-28.3 MPa (3100 to 4100 p s i ) , and for 24 hours. The four systems were based on the following polymers: EPDM, FKM, EPDMIFKM Blend, and Propylene- TFE. objectives and show d e f i n i t e improvement over elastomer compounds which are commercially available. measurable improvement of the hydrothennochemical s t a b i l i t y was achieved i n the synthetic geothermal brine. A laboratory simulator was designed and fabricated which operational packer. This provides the f u l l Upon conclusion of the development, compounds based on four A l l four elastomer systems successfully exceeded the contract Over the duration of the program, Figure 2 shows post mortem test specimen of one of the better, earlier EPDM compounds, seal 217-11-1. f u l l y a t 26OoC, but did suffer a s i g n i f i c a n t level of extrusion. This element sealed success- In Li2 15-4 contrast, one of the latest Compounds is shown, post m o r t e m seal 275-1, which is an EPDM/F lend. Only a minor amount of permanent deformation resulted and xtrusion; the seal had an excellent appearance when removed from the test. This element sealed successf u l l y under the same conditions as 217-11-1 except even a higher d i f f e r e n t i a l pressure, 24.8 vs. 21.4 MPa (3600 vs. 3100 p s i ) . t i o n of the accomplishments is the O-ring S est data which compares the developed compounds against a ted number of commercially available compounds. The packer SIM T e s t was modified for static simulation t e s t i n g of O-rings. The 2-329 O-ring groove is of standard commercial dimensions with no back-ups. clearance is 0.229 mm (0.009 in.), quite severe for the test conditions. The O-rings w e r e tested at 26OOC i n the synthetic geothermal brine s t a r t i n g at 28.3 MPa (4100 psi) d i f f e r e n t i a l pressure. The test was set for 22 hours and i f a compound f a i l e d before 22 hours, the differential pressure was decreased by 6.9 MPa (1000 psi) and the test rerun with a new seal. The-reduction i n d i f f e r e n t i a l pressure progressed to 14.5 MPa (2100 psi) where the t e s t i n g stopped i f the compound f a i l e d . Because t h i s is an unusually severe environment, the GEM compounds have a d i s t i n c t advantage i n t h a t they w e r e developed s p e c i f i c a l l y for t h i s condition. Figure 3 summarizes t h e r e s u l t i n g capability measured for each of the compounds. The GEM 255 FKM and 267 EPDM compounds performed better than t h e i r commercial counterparts. The 255 FKM held for the e n t i r e test period at 21.4 MPa (3100 psi) while the commercial counterparts both broke at 14.5 MPa (2100 psi). The GEM 267 EPDM looked excellent a f t e r the 28.3 MPa (4100 psi) run and is capable of higher d i f f e r e n t i a l pressures while its counterparts showed i n c i p i e n t f a i l u r e . There w e r e no commerc i a l l y comparable counterparts for the EPDM/FKM Blend or the Propylene-TFE, both ran the f u l l 22 hours at the f u l l d i f f e r e n t i a l pressure. The Blend looked as good as the 267 EPDM and, hence, is also capable of higher d i f f e r e n t i a l pressures and the Propylene-TFE suffered minor extrusion. There was no counterpart to the DuPont Perfluoroelastomer (KalrezR), however, it is of keen i n t e r e s t because it is one of the more chemically s t a b l e polymers. sive but its expense is j u s t i f i a b l e i n some,situations because of the longer l i f e it renders. For the synthetic geothermal brine environment the 3074 Perfluoroelastomer did not fare as w e l l as the four developed compounds i n the O-ring test, and earlier coupon ageing tests were made on 3073 Perfluoroelastomer which indicate t h a t it is not as hydrothermochemically s t a b l e as the developed compounds. may r e s u l t i n si lar improvements as was i n accomplished. ,more i n t e r e s t i n g seals; 267 EPDM, E-692-75 EPDM, 266 EPDM/FKM Blend, and the Perfluoroelastomer 3074. 28.3 MPa (4100 p s i ) d i f f e r e n t i a l pressure except the Perfluoroelastomer 3074 which ran at 14.5 MPa (2100 p s i ) d i f f e r e n t i a l pressure. 0-Rinq Simulation T e s t s -- Anoth good quantitative demonstra- The measured It is very expen- Specific compounding for the geothermal brine environment Figure 4 is a compos te photograph o A l l Seals ran Successfully for 22 hours at 15-5 N o t e 'that the 267 EPDM and 'the 266 EPDM/FKM Blend look excellent, although some permanent squaring of the O-rings did occur. Both the E-692-75 EPDM and the Perfluoroelastomer 3074 are seen to have suffered damage.

 

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