Reservoir Compaction, Surface Subsidence, and Casing Damage: A Geomechanics Approach to Mitigation and Reservoir Management

Abstract

Geologic, and historical well failure, production, and injection data were analyzed to guide development of three-dimensional geomechanical models of the Belridge Diatomite Field, California. The central premise of the numerical simulations is that spatial gradients in pore pressure induced by production and injection in a low permeability reservoir may perturb the local stresses and cause subsurface deformation sufficient to result in well failure. Time-dependent reservoir pressure fields that were calculated from three-dimensional finite difference reservoir simulations were input into three-dimensional nonlinear finite element geomechanical simulations. The reservoir models included nearly 100,000 gridblocks (100-200 wells), and covered nearly 20 years of production and injection. The geomechanical models were meshed from structure maps and contained more than 300,000 nodal points. Shear strain localization along weak bedding planes that causes casing dog-legs in the field was accommodated in the model by contact surfaces located immediately above the reservoir and at two locations in the overburden. The geomechanical simulations are partially validated by comparison of the predicted surface subsidence with field measurements, and by comparison of predicted deformation with observed casing damage. Further, simulations performed for two independently developed areas at South Belridge, Sections 33 and 29, corroborate their different well failure histories. The simulations suggest the three types of casing damage observed, and show that although water injection has mitigated surface subsidence, it can, under some circumstances, increase the lateral gradients in effective stress, that in turn can accelerate subsurface horizontal motions. Geomechanical simulation is an important reservoir management tool that can be used to identify optimal operating policies to mitigate casing damage for existing field developments, and also applied to incorporate the effect of well failure potential in economic analyses of alternative infilling plans and operating strategies. P. 403

Mechanical Compaction of Porous Sandstone

“…For very porous or weakly consolidated reservoirs, the increase in effective stress may be sufficient to cause inelastic deformation of the reservoir rock (e.g., Jones and Leddra, 1989;Goldsmith, 1989). The consequences of such inelastic compaction can be economically severe and include surface subsidence and various production problems (e.g., Smits et al, 1988;Fredrich et al, 1998). Significant reduction of permeability may also accompany the compaction (Zhu and Wong, 1997b).…”

“…In such cases, the inelastic deformation may lead to casing failure or solids production, both of which may be serious enough to force well abandonment (e.g., Fredrich et al, 1998). Knowledge of the compactive response of rock masses to stress is also relevant to various geotechnical applications, including drilling technology (e.g., Thiercelin, 1989;Suarez-Rivera et al, 1990), and nuclear waste isolation (e.g., Davis, 1991).…”

Iterative Coupled Analysis of Geomechanics and Fluid Flow for Rock Compaction in Reservoir Simulation

“…In general, the coupled analysis of geomechanics and reservoir fluid flow can be classified into three types (e.g., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]). They are loosely coupled, iterative fully coupled, and simultaneously fully coupled.…”

“…Also, it may be difficult to develop a robust and effective numerical procedure for simultaneously solving the coupled system of equations that combines geomechanics and reservoir multiphase flow. On the other hand, depending upon the degree of coupling that varies between one-way coupling to explicit coupling (e.g., [1][2][3][4]), the loosely coupled analysis has low computing cost and at best provides only an approximate solution to the true solution of the coupled problem. The iteratively coupled analysis decomposes the coupled system of equations into two subsystems of equations that correspond to the governing equations of the reservoir simulator and of the geomechanics model.…”

Constitutive models for the Etchegoin Sands, Belridge Diatomite, and overburden formations at the Lost Hills oil field, California

“…Central to the numerical modeling work has been the use of sophisticated material models that capture accurately the highly non-linear deformation behavior of the reservoir rock, including inelastic compaction (yield) at stress states below the shear failure surface. Fredrich et al (1996Fredrich et al ( , 1998Fredrich et al ( , 2000 described the development of three-dimensional geomechanical models for the Behidge field and the historical simulations that were performed collaboratively with Shell E&P Technology Co. and Aera Energy LLC for Sections 33 and 29 using Sandia National Laboratories' quasi-static large-deformation structur@ mechanics finite element code, JAS3D (Blanford et al, 1996). JAS3D provides several constitutive models to simulate time-independent elastic and inelastic (non-linear) deformation as well as time-dependent (creep) behavior.…”