Effective Geomechanical Modeling of Geologic Structures, 20-R9665Printer Friendly Version
Inclusive Dates: 10/01/06 Current
Background - Although numerical modeling is a well-established tool in many scientific and engineering areas, the oil and gas industry has been hesitant to employ geomechanical modeling in the upstream phases of hydrocarbon prospect evaluation and reservoir characterization. A contributing factor to this reluctance is the short time scale for decision making compared to the typical time needed to build and analyze a representative geomechanical model. Furthermore, the uncertainties in boundary conditions and material properties often lead to poorly constrained problems that are difficult to validate against available field data.
Approach - The objectives are to develop an efficient workflow and set of best practices for effective numerical geomechanical modeling of hydrocarbon field-to reservoir-scale geologic structures by an analysis of a case example geologic structure. Big Brushy Canyon monocline in west Texas is an excellent analog for a common hydrocarbon reservoir structure in many Arabian Gulf oil fields, and the study site provides sufficient exposure so that field observations and measurements can be compared to model predictions to validate the model. The fundamental project plan includes field characterization to define the structural geometry and collect the data necessary for model validation; two-dimensional numerical modeling (both finite element and discrete element); probabilistic analyses to assess the importance of parameters such as boundary conditions and material properties on numerical model predictions; three-dimensional numerical modeling that is conditioned by the best parameter estimates derived from the probabilistic modeling; and development of an efficient but general workflow and a set of best practices.
Accomplishments - Team members conducted field work in Big Brushy Canyon. Efforts focused on constraining the three-dimensional geometry of the monocline; collecting oriented rock samples for microstructural analyses; and collecting fracture orientation and spacing measurements from the Santa Elena Limestone in the footwall near the fault. Two-dimensional finite element models of the monocline developed in ABAQUS® successfully replicated the monocline geometry and provided layer-parallel extensional strain and bedding-plane slip data for quantitative comparison to the field observations. Probabilistic analyses revealed that the numerical model results were more sensitive to the material properties of the stratigraphic intervals than to the strength of the frictional interfaces between layers. Refined numerical modeling continues based on insights gained from probabilistic analysis results. This integration of mechanical and probabilistic analysis techniques provides an innovative and robust approach to both guide iterative mechanical modeling and results evaluation, providing an improved understanding of reservoir deformation and uncertainties in reservoir conditions.