THE INFLUENCE OF FAULT PERMEABILITY ON SINGLE-PHASE FLUID-FLOW NEAR FAULT-SAND INTERSECTIONS - RESULTS FROM STEADY-STATE HIGH-RESOLUTION MODELS OF PRESSURE-DRIVEN FLUID-FLOW

By integrating numerical analysis with field information, we have deve loped realistic cross-sectional models of faulted sand-shale sequences at 3 km or greater depth to investigate how fluid-flow patterns vary with fault permeability, Simulated (isotropic) permeability ranges for shale were 10(-19) to 10(-17) m(2) (porosity phi = 10-35%) and for sa nd were 10(-14) to 10(-12) m(2) (phi = 20-25%). Fault permeability ran ged between 10(-21) to 10(-12) m(2) among four models. Our results wer e obtained with a novel multigrid finite-element technique allowing th e rapid solution of fluid flow on very fine meshes that represent thin faults and interlayered sand-shale strata with their correct aspect r atios (up to greater than or equal to 800: 1) and incorporate permeabi lity contrasts with the country rock of up to ten orders of magnitude. Pressure-driven flows have been calculated for boundary pressures, si mulating a transition from hydrostatic to 0.8 lithostatic with increas ing depth, The four high-resolution models show that fault permeabilit y and juxtaposition relationships across the fault control hydrodynami c fluid-flow patterns, The greater the difference between the permeabi lity of the fault and that of the undeformed country rock, the more th e flow patterns differ from those predicted by a simple geometrical an alysis of sand-juxtaposition relationships across the fault, assuming that flow occurs only across overlapping sands, In our small-scale mod els and in another idealized basin-scale model of pressure;driven flui d flow, the direction of flow in faulted sand units can be reversed by changing the fault permeability, This two-dimensional result may indi cate a wide range of hydrodynamic transport scenarios for hydrocarbons in basins where fault permeability changed with time.