Evaluating Controls on Cross-fault Flow within Reservoirs

Abstract

Flow across a series of simulated faults were modeled to evaluate how variation of fault properties (juxtaposition, complexity, and fault rock) affect upscaled fault flow resistance. . Simulations with cell size similar to that typical of reservoir simulators overestimate juxtaposition flow resistance. Juxtaposition flow resistance also deviates where upscaled reservoir cells near the faults contain a significant fraction of shale. Fault complexity in the absence of fault rock adds little flow resistance to that created by juxtaposition along a single shear plane. Continuous, tight fault rock causes the greatest flow resistance. However, the presence of even a small number of high-permeability pathways through the barrier greatly reduce its flow resistance. Overall, the major cross-fault flow control is continuity of tight fault rock. Where the fault rock is not continuous, flow resistance is low and controlled by the fault architecture. Where tight fault rock is continuous, flow resistance is high and controlled by fault rock properties. The abruptness of change between low flow resistance with discontinuous barriers to high resistance with continuous barriers is controlled by the ratio of reservoir to fault rock flow resistance.