SENSITIVITY STUDY OF FLOWING GAS COMPOSITION FOR WELLS IN SHALE GAS RESERVOIR

Because of the ultra-low permeability of the shale-gas reservoir, the transient flow in these reservoirs can last many years and radial flow is very di cult to reach, which makes the pressure transient analysis impractical. Transientrate-analysis methods as a substitute for pressure transient analysis to determine reservoir parameters have become very popular in recent years. However, due to the absence of the flowing well pressure and low-frequency, low-resolution production data, diagnosis of production data su ers from uniqueness and uncertainty. Composition of di erent gas components change with time has been reported in the gas-condensate reservoirs and the shale-gas reservoirs. In this paper we use a compositional model incorporating extended Langmuir isotherm and apparent permeability to study flowing composition transient response. First, a dry gas compositional model is established to model flow of components in the shale-gas reservoirs. Then, fully implicit linearization of the equation system is employed to solve the nonlinear equation system based on unstructured gridding. Numerical simulation shows that adsorption gas content, porosity and permeability a ect the characteristics of flowing composition, composition change and composition derivative. Adsorption gas content determines drop speed of composition, the value of composition change and composition derivative for CH4 component. Permeability a ects composition transient response during early stage. However, during the medium and late stages, di erent permeabilities have the same influence on the composition transient response. The e ects of porosity and adsorption gas content on composition change and composition derivative are similar. However, small difference exists for the e ects of porosity and adsorption gas content on composition change with time at early stage. The findings in this paper would provide a new way to interpret the shale-gas reservoir parameters.