Eagle Ford Water Management Strategy, Piloncillo Ranch, Southwest Texas

Southwest Texas is commonly associated with sprawling ranches, mesquite for miles, and phrases like “whiskey’s for drinking and water’s for fighting”. In the last few years this region has experienced an unprecedented activity boom related to the development of the Eagle Ford shale formation. Sustainable development is imperative given the scarcity of water in the area and the large volumes of water required for hydraulic fracturing. Shell has a multi-pronged approach to its water management strategy. Our goals are to minimize our impact on the Carrizo aquifer by using alternatives where available, treat/reuse water as possible and have disposal options that protect potable water.

The appraisal program at Piloncillo Ranch involved logging both Eagle Ford wells and Carrizo water wells from surface to total depth. This data was then used to characterize the different geologic formations. Several zones were identified that could be used for either disposal or for providing brackish water. Express pressure tools were run in five wells dispersed across the 106,000 acre ranch. This data was used to determine pressure gradients and mobility/permeability. Shell also drilled a water well into the Wilcox and collected samples that are being used to qualify the brackish water for hydraulic fracturing. Numerical groundwater flow modeling using MODFLOW was accomplished by updating a preexisting Texas Water Development Board model to simulate sourcing or disposing at Piloncillo Ranch. New inputs/updates to the model included grid refinement, yield, capacity, drawdown, local horizontal and vertical permeability, and extraction wells.

Testing the brackish upper Wilcox resulted in a secondary fracture water source. Model results established a sustainable timeline, rates, and volumes that the Carrizo and Wilcox aquifers could support based on current groundwater extraction forecasts. Injection and withdrawal simulations suggest negligible interaction between the upper Wilcox and Carrizo. Injection into the lower Wilcox, at a rate determined by disposal forecasting, had little impact on the upper Wilcox and Carrizo, which is supported by the permeabilities derived from the pressure tests and the geologic interpretation of the logs, where several massive aquitards were identified. We will be able to reduce the volume of fresh water extracted from the Carrizo aquifer by blending with brackish water and manage disposal by treating and reusing produced water.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California