MODELING THE FLUID FLOW IMPLICATIONS OF VARYING FAULT PERMEABILITY STRUCTURE ALONG THE TEASDALE FAULT, UTAH

Exhumed reservoirs help to assess subsurface uncertainty in the presence, type, orientation and intensity of fault-related damage elements (e.g., joints and deformation bands). Outcrop analogs for groundwater and petroleum production found along the 40-km Teasdale Fault (cutting aeolian Navajo Sandstone) help to evaluate possible implications of incorrectly estimating damage element properties. Single-phase, transient, finite-element fluid flow simulations are used to explore geologically plausible fault-related permeability (k) structures at two locations along the fault. At the fault mid-point, displacement is reverse slip (~1.5 km). At one end, displacement is strike-slip (~200 m). Simulated artesian conditions cause production wells to discharge water at declining rates computed in the simulations. Damage element attributes (e.g., permeability, porosity, width, continuity) and their location are based on detailed field mapping of fault-affected rock at each study location. Typical joint zone k values (k_fn = fault-normal, k_sp = strike-parallel, k_dp = dip-parallel) are anisotropic with k_fn = 379 md, k_sp = 3631 md and k_dp = 2508 md. Deformation band zones are nearly isotropic with k_fn = 7 md, k_sp = 14 md and k_dp = 22 md. Varying these properties shows how intersecting zones of joints and deformation bands affect production from two hypothetical well fields. Simulation results indicate that high-k joint zones have a greater impact on drawdown and discharge volumes than low-k deformation band zones. The most restricted and compartmentalized systems yield cumulative production volumes 30% of the most connected systems. Thus, it is important to distinguish between subsurface joint zones and deformation band zones. Differences in cumulative production from individual wells illustrate how incorrectly estimating damage element properties may lead to poor well placement. Individual wells discharging from the least productive system can yield as little as 11% that of the most productive system. Simulation results show that the more closely spaced damage element zones of the reverse slip locality affect well production to a greater degree than the more widely distributed zones of the strike-slip locality. In both cases, production can be maximized by drilling wells near, or through the permeable joint zones.