Numerical Modeling of Regional Ground Water Flow in the Deep-Brine Aquifers of the Palo Duro Basin, Texas Panhandle




Wirojanagud, Prakob
Kreitler, Charles W.

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A conceptual hydrogeologic model of the Palo Duro Basin, Texas Panhandle, subdivides the basin into three hydrogeologic units: the shallow Ogallala and Dockum aquifers, the Permian evaporite aquitard, and the deep confined, underpressured Permian and Pennsylvanian brine aquifer. The first permeable units beneath the thick Permian evaporite section are Wolfcamp strata composed of carbonates, shales, and arkosic sand and gravels (granite wash) with average effective permeability values of 8.9, 0.0001, and 8.6 md, respectively. Groundwaters in the Wolfcamp aquifer flow to the northeast toward the semi-impermeable, granitic Amarillo Uplift. This anomalous hydrologic condition (flow toward a low-transmissivity barrier) may result from the presence of highly permeable granite-wash deposits that flank the uplift and function as "hydrologic sinks."

A two-dimensional, vertical-averaging finite-element model, incorporating the different lithologies and their different permeabilities as well as leakage through the overlying evaporite aquitard, has been used to simulate the observed potentiometric surface of the Wolfcamp aquifer. The conditions that best simulate the observed Wolfcamp potentiometric surface are a combination of specified head and no-flow conditions along the uplift, permeability values greater than 260 md for the granite-wash deposits that flank the uplift (in contrast to the average value of 8.6 md), and an increased permeability value of 50 md for the highly porous carbonate zone. The best estimate of the vertical permeability of the evaporite aquitard is 0.00008 md.

Treating the whole deep-brine aquifer as a single permeable unit beneath the evaporite aquitard, groundwater flow is to the northeast toward the uplift with a slightly larger west-to-east component than that found when considering only flow in Wolfcamp strata. The conditions that best simulate the averaged potentiometric surface are those from the best simulation of Wolfcamp strata, with increased permeability values of 260 md for the Pennsylvanian granite-wash close to the uplift and 250 md for the high-porosity Pennsylvanian sandstone.


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