Large-Scale Three-Dimensional Geomechanical Modeling of Reservoirs: Examples from California and the Deepwater Gulf of Mexico

Large-Scale Three-Dimensional Geomechanical Modeling of Reservoirs: Examples from California and the Deepwater Gulf of Mexico — Cost-effective improvements in the technology needed to develop and manage reservoirs in challenging environments require an increase in our understanding of geomechanical behavior. The local stresses relevant to reservoir-scale processes are strongly affected by stratigraphic and structural features at that scale, and the relationship between hydrocarbon production and the mechanical behavior of the reservoir and/or overburden can be complicated and difficult to discern from field data directly. Numerical simulation provides a means to achieve critical insight into the behavior of complex geosystems and advance understanding of both the subsurface environment before drilling as well as the relationship between fluid flow and geomechanical behavior during production. This paper reviews our recent work aimed at utilizing large-scale geomechanical simulation as a reservoir management tool. We first describe the constitutive models developed specifically for two important classes of geomaterials that are implemented in the quasi-static largedeformation finite element code JAS3D that we use in our work. We then describe several field cases where we apply nonlinear finite element modeling to key problems in reservoir mechanics. The first field cases involve historical geomechanical simulations of primary and secondary recovery at the Belridge Diatomite and Lost Hills fields located in California’s San Joaquin Valley. In this work, we apply nonlinear finite element modeling to investigate the causes of well casing damage experienced by the field operators and to identify mitigation strategies. Next, we describe an application that addresses potential well integrity issues associated with sub-salt and near-salt deepwater Gulf of Mexico reservoirs. In this work, we analyze hole closure behavior and quantify loading on casings for wells that penetrate thick salt formations to ensure that wells are designed to withstand salt loading over a service lifetime of 20-30 years. The field studies illustrate the difficult issues encountered in practical applications of large-scale three-dimensional nonlinear finite element geomechanical modeling and suggest areas where research advances could be beneficial. These areas include: development of solids models and finite element meshes from disparate geologic and/or numerical data, development of realistic constitutive models, robust and efficient implementation of these material models in finite element codes to achieve reasonable solution times, experimental rock mechanics data and the natural heterogeneity of geosystems, implementation of far-field (tectonic) stresses and stress initialization, and integration of geomechanical modeling results with other analysis tools. JT Fredrich and AF Fossum / Large-Scale Three-Dimensional Geomechanical Modeling of Reservoirs modeling. The first field cases involve historical geomechanical simulations of the Belridge Diatomite and Lost Hills fields located in California. In this work, nonlinear finite element modeling is applied to investigate the causes of well casing damage experienced by the field operators and to identify mitigation strategies. The approach includes the development of large-scale three-dimensional geomechanical models (hundreds of thousands of finite elements) and unidirectional coupling between three-dimensional black oil reservoir models and geomechanical models. Next, we describe a field application that addresses well integrity issues associated with sub-salt and near-salt deepwater Gulf of Mexico (GoM) reservoirs. In this work, we analyze hole closure behavior caused by salt creep and quantify loading on casings for wells that penetrate thick salt formations to ensure that wells are designed to withstand salt loading over a service lifetime of 20-30 years. Besides directly demonstrating both the feasibility and benefits of large-scale three-dimensional non-linear finite element geomechanical modeling, the field cases also illustrate the difficult issues encountered in practical applications. We close by discussing these issues and the approaches that we have taken to circumvent some of these difficulties. We also suggest areas where research advances would be beneficial. 1 COMPUTATIONAL GEOMECHANICS