Hydromechanical modeling of tectonically driven groundwater flow with application to the Arkoma Foreland Basin

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Abstract
Deep groundwater flow can be driven by several mechanisms in sedimentary basins. In the case of evolving foreland basins, large‐scale compression and thrusting could develop abnormally high pressures in the foreland sag that would initiate transient fluid flow. The so‐called tectonic “squeegee” effect is thought to have caused basin‐wide migration of ore‐forming brines and hydrocarbons (Oliver, 1986). Two‐dimensional numerical models are developed here to quantify the role of compressional tectonics in driving regional fluid flow in the later stages of thrusting in a foreland basin. Poroelasticity theory coupled with regional groundwater flow form the basic elements of the mathematical model. We use the mathematical model to predict deformation and pressure dissipation in the unfaulted and nonfolded part of a foreland basin in front of a thrust belt as it is subjected to an instantaneous loading event. Sets of numerical experiments show that overpressure zones develop along the leading edge of the thrust belt near the loading front. Stress‐induced flow rates of the order of centimeters to meters per year are possible soon after compression of the foreland, and transient flow fields dissipate in about 103 and 104 years. Longer transients can exist in very low permeability strata. Large overpressures may be unable to buildup under conditions of gradual thrusting, as fluid pressures may dissipate too quickly. The general features of tectonically driven flow are also explored through a sensitivity study to consider effects of permeability, fault and stratigraphic heterogeneity, loading magnitude, and variations in rock compressibility. The sensitivity study is based mostly on numerical experiments. As these solutions suffered from stability problems in cases where bulk rock compressibility exceeded 10−9 Pa−1, some simple scaling arguments are used to extend the numerical results for squeezing of soft shale. One basin‐specific application to the Ouachita orogen suggests that tectonic squeezing could have caused transient flow systems with relatively large flow velocities in basal Cambro‐Ordovician aquifers. The volume of fluid expelled, however, is probably only a small fraction of the total brine volume needed to have formed the huge Mississippi Valley‐type lead‐zinc ore deposits fringing the northern margin of the Arkoma Basin on the Ozark Uplift.