brine injection studies

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Brine Injection StudiesMarcclo J Lippmann

L a w r e n c e B e r k e le y Laboratory, Earth S c i ences D i v i s i onU n i v e r s i t y of C al i f o r n ia , B e r ke l ey , C a l i f o r n i a 94720

ABSTRACTT h e p r o g r a m of the Lawrence Berkeley Laboratory inBrine Injection Technology is comprised of field and theoreticalactivi t ies. Emphasis is given to t h e s t u d y of migrat ion ofinjection fluids and comp osit iona l eflects in t he reservoir , andopt imizing the heat ext ract ion f rom geothermal sys tems. Ajoint inject ion tes t program wi th indust ry has also been ini-t i a ted. Th e resul t s of the FYI985 eflort and the proposedplans for FY1986 are described.

INTRODUCTIONTh e overal l purpose of t he Lawrence Berkeley Lab oratoryBrine Injection Project is to develop and demonst ra te methodsfor predict ing, monitoring and analyzing the short and long-term response of geothermal reservoirs to fluid reinjection.The project addresses the main reservoir engineering issues inbrine injection Ta bl e l , which can be summarized by the following three s ta tements : 1) predict , cont rol and moni tor themovement of the inject ion plume, 2) maintain, and if poesibleincrease, the injection capacity of the wells and 3) opt imizethe production-injection system t enhance the heat ext ract ionfrom the reservoi r and reduce thermal degradat ion of produc-ing wells.

SUMhURY, OF MOST IMPORTANT FY1985A C T M T I E ~Modeling o j sharp jronts. Numerical dispersion is a seri-ous problem i n model ing shar p thermal or composit ional )fronts associated with injection plumes. A second-orderupwind/central difference method for convection-diKusion typeof equations that greatly reduces numerical diffusion errors hasbeen developed Lai e t al . , 1985). On Figure 1 a compar i sonbetween the sha r pnes s of a modeled front using the conven-tional upwind-difTerence num erical schem e grap hs on the left)

IS compar ed , for diflerent injected volumes, with th at obtaine dwi th the new approach graphs on the r ight ) . A much sharperf r o n t . that closely matches analytical resu l t s , is given by Lai etal.s method

Table 1. M a i n IMU- In B r i n e I n j e c t io n

Predict ion and moni tor ing of migration of injectionfluidshlaintain ing well injectivi tiesAnalysls of hrat extraction and composit i ional effectsin geothermal reservoirs during injectionDevelopment and improvem ent of mathem at ical toolsto rnotlt*I pro crss rs r elrv ant to t h e migration ofinjected f l u id5 in t h r rese rvo i r

LBL--20415DE86 006290

Compositional EJects We developed the capabil i ty ofmodeling heterogeneous re actions between solid phases andgaseous com ponents under geoth ermal reservoir condi t ionswhich has been applied to s tudy the or igin of CO, n the Lar-derello field Pru ess et al., 1985). This ef lor t complements ourprevious modeling work on H20/C02 mixtures for differentphase comp osit ions OSullivan et al. , 1985).Th e dissolution a nd precipi ta t ion of silica in nonisother-mal sys tems are being s tudied, includi rg the cor respondingchan ges in reservoir porosity an d permeabil i ty Lai et al .,1985b; V e r m a a n d Pruess, 1985). Equil ibrium as well askinetic relat ionships for silica-water reactions have beendeveloped an d incorporated in k, exist ing LBL compu ter codes .Heof Erfracfion Sfudies. Thi s year we completed themodeling of Stanfords heat ext ract ion exper iments us ing themethod of mul t iple interact ing cont inua MINC; ruess andN ar as i mhan , 1985). A chapter of a Lam et a l . 1985) epor t ,describing the LBL modeling code and involvement in the pro-ject , was cont r ibuted by IC. Pruess .To more accurately describe fractured geothermal reser-voirs the MIN method was extended to include variat ions infract ure spacing. Th is will allow a more realistic modeling ofthe heat transfer between irregularly shaped rock blocks andadjoining f ractures .Analys is OJ Injection Test in Fractured Reservoirs.Models to analyze injection tests in geothermal systems haveto consider nonisothermal eKects and the f ractured nature ofthe reservoir; otherw ise wrong permeabil i ty-thickness produ ctswill be obtained. C o x and Bodvarsson 1985) tudied pressuretransients result ing from nonisothermal injection into horizon-tal and vert ical fractures with variable rock matrix and frac-t u r e pa rame t e r s F i gure 2). T hey s h o w that the pressure isgreatly controlled by the moveme nt of t he t he r ma l f r o n tt h r o u g h the f ractures , because of the t emperature-dependentfluid propert ies. These eKects are quite difTerent than thoseder ived for porous sys tems because of unlike thermal frontadvance ra t e s. T h i s s t udy also describes differing pressureda t a ana l ys is p r ocedur es t ha t depend on the geometry vert icalversus hor izontal ) of the fractures and the propert ies of theinjected and reservoir fluids.Evaluation of Composite Reservoir Systems. A new tech-nique was developed for evaluating well interference test d a t ain radial ly symme tric composite reservoirs Benson and Lai,1985). By analyzing var ia t ions in the apparen t s toragecoefficient , both the mobil i ty k / p ) and the size of the innerregion can be calcula ted. Th e technique is particularly usefulfor evaluating heterogeneous systems where t h e intersection ofaeveral faults or hydrothermal a l tera t ion has created a zone ofhigh or l ow) permeability region i n t h e center of geothermalfield T h e method h a s been applied to characterize theK l amat h F a l l s , O r egon , sys t r m F i gure 3 ) .


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-0.143 Pore300-0.143 PoreVolumes Injected Volumes Injected

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400 1 1 1 * 1 1 1 * . . 1 1 . . 1

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XBL 858-10715Figure 1 Comparwn between results using the conventional first-order upis iiidd i k e n c e s ch e me ( l ef t c olu mn g r a p hs ) a n d the monoionized up\r i i id centraldiRerence scheme or La1 et a1 1985b (right column gr:ipli>) Fluid I> i i i j ~ i ~ lin t h e loucr l c f t corner and extracled from the upper left corncr of the 5 ) s -tem. linrs represent isocons

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Horizontal fracture3 0 -2.5 - Tm = 1, 1oooC

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Time sec)Figure 2. Pressure transients da ta for nonisothermal injection into a horizontal fractureCox and Bodvarsson, 1985).

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1200 2400

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Figure 3 i l igh-permeability r e g i o n inferred in t h e Klamath Falls geoitlrrmal tirltl b : ~ don ttir rompositr-rrsrrvoir analyse of Benson and La1 ( I J S 5 )


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brine injection studies

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