The flow of nitrogen and brine in tight Vicksburg "P" Sand cores was studied under field stress conditions. The experiments simulated various stages of a hydraulic fracturing treatment. Measurements were made of critical gas saturation, gas flow vs pressure gradient, and gas permeability vs brine saturation. Brine saturations were imaged with a medical Computerized Tomography (CT) scanner.

The laboratory results suggest that water block is not important when drawdown pressures at the fracture face exceed the capillary entry pressure by several hundred psi. The addition of alcohol or an alcohol/surfactant package to the brine does not significantly increase final gas flow.

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