Subsidence and Well Failure in the South Belridge Diatomite Field

Abstract

Shell Development Co.; and S.K. Hara," Shell Offshore Inc. q SPE Members Copyright1995, Sodety of PetroleumEngineers,Inc. Thw paper wea preperedfor presentationat the Western RegionalMeethg held in Bakersfield,CA, U.S.A., S-10 March 1SS5. Th@PSPWwss selaotedfor preeentatbnby an SPE ProgramOommittaefolfowingreviewof informationcontainedIn an abatrsoleubmittadby the authef(s).Contentsof the paper, es presented,have not bean reviewedby the Sooiity of PetroleumEngineersand era sub@t to oormotionby the author(s).The material,se pWSSntW$ dOSenOtn--lY re~of enY~tl~Ofthe -kfy of PStdeUM Engineers,its officers,or members.Paperspresentedat SPE meetingsare aubjeotto publication ravkw by EditorialCommHtees of the .%cIefy of Pafm$aum Engineers. Permission toqy !srestricted toan stmtrect ofnotmorethan300 words.Illustmfiona mayI-Wb oapiad.The sbatrsct shouldcontainconapicucua acknowkdgmant of where end by whomthe pspar is presented.Write Librarian,SPE, P.0, Sox SSSS3S, Rkhardaon, TX 750s3-SS3S,U.S.A., Telex 1SS24.5SPEUT. ABSTRACTWithdrawal of fluids from shallow, thick and low strength rock can cause substantial reservoir compaction leading to surface subsidence and wel! failure. This is the case for the Diatomite reservoir, where over 10 ft of subsidence have occurred in some areas. Well failure rates have averaged over 3°/0 per year, resulting in several million dollars per year in well replacement and repair costs in the South Belridge Diatomite alone. A program has been underway to address this issue, including experimental, modeling and field monitoring work. An updated elastoplastic rock law based on laboratory data has been generated which includes not only standard shear failure mechanisms but also irreversible pore collapse occurring at low effective stresses (< 150 psi). This law was incorporated into a commercial finite element geomechanics simulator. Since the late 1980s, a network of level survey monuments has been used to monitor subsidence at Belridge. Model predictions of subsidence in Section 33 compare very well with field measured data, which show that water injection reduces subsidence from 7-8 inches per year to 1-2 inches per year, but does not abate well failure.The model has been used to infer potential well failure mechanisms resulting from fluid withdrawal policies and to estimate the impact of alternative operating policies for a 5/8-acre waterflood project; results show that aggressive operation of a newly completed producer can potentially damage a nearby well and that 1/1 producer/injector ratio results in significantly less subsidence and lower shear strains than a 3/1 ratio.

Estimating fluid-induced stress change from observed deformation

“…Because the fields in the San Joaquin Valley are characterized by soft and porous formations that are quite thick and rather shallow, oil production has generated observable subsidence at the ground surface (Bowersox & Shore 1990;Bruno & Bovberg 1992;De Rouffignac & Bondor 1995). Such subsidence has been actively monitored in several fields.…”

“…Well failures, due to reservoir deformation, have accompanied oil production from fields in the San Joaquin Valley of California (Bruno & Bovberg 1992;De Rouffignac & Bondor 1995;Myer et al 1996;Fredrich et al 2000). For this reason several studies explored the failure characteristics of diatomite, the main reservoir rock (De Rouffignac & Bondor 1995;Fossum & Fredrich 1998;Fredrich et al 2000), and of the overlying sediments where many of the well failures tend to occur (Bruno & Bovberg 1992;Fossum & Fredrich 2000;Fredrich et al 2000).…”

“…For this reason several studies explored the failure characteristics of diatomite, the main reservoir rock (De Rouffignac & Bondor 1995;Fossum & Fredrich 1998;Fredrich et al 2000), and of the overlying sediments where many of the well failures tend to occur (Bruno & Bovberg 1992;Fossum & Fredrich 2000;Fredrich et al 2000). The Drucker-Prager (Drucker & Prager 1952), Cam-Clay (Roscoe et al 1958), and the ESR model (Fossum & Fredrich 2000), an extension of the work of Sandler & Rubin (1979) have been used to model the yield surfaces and shear failure of both the overburden and the reservoir materials.…”

Analysis of Deformation Measurements for Reservoir Managemen

“…If a successful deconvolution of reservoir deformation is achieved, it can help provide answers to many questions that arise in typical production management activities (Wallace and Pugh, 1992;de Rouffignac et al, 1995;Bruno and Bovberg, 1992;Houtenbos, 2000;Dusseault et al, 2001): -Where are produced fluids coming from and where are injected fluids going? -What are the geometric parameters of an induced hydraulic fracture?…”

Estimation of constitutive parameters for the Belridge Diatomite, South Belridge Diatomite Field

“…The ESR Cap Model is qualitatively similar to the cap model implemented in the commercial finite element code ABAQUS (Hibbit, Karlsson & Sorensen, Inc.) that was used by Shell E&P in earlier two-dimensional finite element modeling of the Belridge Diatomite Field (de Rouffignac et al, 1995). However, there are several notable differences between the two models.…”