After a gas well is hydraulically fractured, the relative permeability of the reservoir to gas may be reduced when fracturing fluid invades the pay zone. This phenomenon reduces the well's potential productivity and is more pronounced in low permeability gas reservoirs. Efficient clean-up for this fracturing fluid is thus essential in gas reservoirs. As the first step toward this objective, this paper will study the effect of fracturing fluid clean-up using a numerical simulator for gas-water fractured reservoirs.

This study proves that (1) the dimensionless fracture conductivity FCD, (2) dimensionless fracture length,xf/xe, and (3) the formation capillary pressure, Pc, affect the rate and pattern of the clean-up process. It also shows that the pattern of clean-up can cause misinterpretation of post-frac pressure analysis tests. A better understanding of the clean-up pattern promotes correct analysis of pressure tests.

This paper also shows that the optimum fracture conductivity necessary to clean up the formation may be much higher than that necessary to produce the reservoir. Thus, the fracture parameters, especially for tight gas reservoirs, should be designed so a fracturing treatment will yield enough conductivity for efficient clean-up of fracturing fluid.

Pressure build-up data are simulated and the resulting synthetic data are analyzed to study the effect of clean-up on the calculation of reservoir and fracture parameters.

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