Gas permeability model considering rock deformation and slippage in low permeability water-bearing gas reservoirs

Permeability measurement is necessary in oil and gas fields. During the measurement, slippage, rock deformation, and water saturation affect apparent permeability of low permeability sandstones measured by different fluids. It is well known that gas slippage effect is very obvious and crucial in apparent permeability of low permeability sandstones measured for gas. Klinkenberg correlation was proposed to calculate gas permeability and absolute permeability for low permeability sandstones without considering rock deformation and water saturation. Most previous researchers modified the slippage factor b as a function of absolute permeability, porosity, and water saturation. However, few models were proposed for gas permeability calculation, simultaneously considering effects of rock deformation, gas slippage, and water saturation. In this work, Klinkenberg correlation was extended for permeability calculations measured by liquid and gases. The difference between apparent liquid permeability and apparent gas permeability was that gas slippage, which was much more evident from liquid slippage. An apparent gas permeability model was proposed for gas permeability and absolute permeability calculation simultaneously considering rock deformation, gas slippage, and water saturation in low permeability sandstones. The apparent gas permeability is proportional to the term T/p. Both the interception and the slope of the straight line in the T/p–kg plot with Cartesian coordinate were power law functions of net stress and gas saturation. Some experimental data from literature were applied to validate the proposed model. Good agreements between experimental data and those evaluated by the proposed model were obtained. The apparent gas permeability model proposed in this work will be useful to professionals involved in laboratory measurement of low permeability water-bearing rocks, modeling well performance, and gas production forecasting.