Abstract
An appropriate representation of faults is fundamental for hydro-mechanical reservoir models to obtain robust quantitative insights into the spatial distribution of stress, strain and pore pressure. Using a generic model containing a reservoir layer displaced by a fault, we examine three issues which are typically encountered if faults have to be incorporated in reservoir-scale finite element simulations. These are (1) mesh resolution aspects honoring the scale difference between the typical cell size of the finite element (FE) reservoir model and the heterogeneity of a fault zone, (2) grid geometry relative to the fault geometry and (3) fault dip. Different fault representations were implemented and compared regarding those on the modeling results. Remarkable differences in the calculated stress and strain patterns as well as the pore pressure field are observed. The modeling results are used to infer some general recommendations concerning the implementation of faults in hydro-mechanical reservoir models regarding mesh resolution and grid geometry, taking into account model-scale and scope of interest. The goal is to gain more realistic simulations and, hence, more reliable results regarding fault representation in reservoir models to improve production, lower cost and reduce risk during subsurface operations.
Highlights
Since the beginning of the 21st century, the hydrocarbon industry has shifted towards faulted and structurally more complex conventional or unconventional reservoirs, which require a thorough understanding of both the hydraulic and the mechanical reservoir behavior [1,2,3]
Significant differences in the stress and strain patterns are indicated in the results, which are induced by the fault depending on its incorporation in the numerical model
It needs to be ensured that the fault cells do not interlock with the surrounding, stronger and less permeable host rock as this effects both fluid flow through and straining of the fault zone
Summary
Since the beginning of the 21st century, the hydrocarbon industry has shifted towards faulted and structurally more complex conventional or unconventional reservoirs, which require a thorough understanding of both the hydraulic and the mechanical reservoir behavior [1,2,3]. Various numerical modeling techniques have been tried and tested, e.g., finite difference (FD), boundary element (BE), discrete element (DE) and hybrid methods [11,12,13,14,15], but the most commonly used approach for hydro-mechanical reservoir simulations is the finite element (FE) method which the present study focuses on. Such FE reservoir models typically have a lateral size between kilometers to tens of kilometers and applications can range from hydrocarbon and geothermal reservoirs to sites for underground gas storage [16,17,18]. In order to obtain a realistic subsurface representation for reliable stress and fracture predictions as well as fluid flow path analysis, the reservoir models have to take into accounts faults, i.e., discontinuities offsetting the strata, in addition to the lithostratigraphic horizons
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