Stochastic Modeling of Subseismic Faults Conditioned on Displacement and Orientation Maps

Abstract

Subseismic faults are small faults or fractures that may be difficult to determine but can have large consequences for fluid flow and pressure communication in the subsurface. Thus, knowing their distributions may be important in several subsurface applications, such as hydrocarbon exploration and exploitation, geothermal energy production, and subsurface CO₂ injection. The aim of this work is to use a stochastic model to populate a three-dimensional structural model of the subsurface with subseismic faults. The novelty of the proposed method is the conditioning of the stochastic model to input maps describing displacement and stress orientation along subsurface horizons. Hence, the resulting structural model will be consistent with these maps. The maps can originate from a variety of sources, for example, predictions of a geomechanical model or (indirect) measurements of subsurface displacements and stresses. The model uses simulated annealing as the optimization algorithm, where the residual between the displacement of the modeled subseismic faults and the input displacement map is minimized through an iterative process. Each subseismic fault is modeled with a three-dimensional displacement field around the fault slip plane, enabling comparisons with the input displacement map along a horizon. An example of how the model distributes the subseismic faults around larger known faults, using a synthetically created displacement map, is provided. The result shows that the model quickly converges towards a set of subseismic faults, giving total displacement and strike orientation close to the input maps.