Production effect evaluation of shale gas fractured horizontal well under variable production and variable pressure

Abstract Most shale gas production prediction models are established on the ideal production conditions (the constant pressure and constant production condition), deviating from the production performance characteristics of shale gas wells with variable production and pressure and leading to large error in unknown model parameter inversion of the actual shale gas wells, and obviously showing great limitations in characterizing the dynamic production performance and predicting EUR of shale gas wells for variable production-pressure. Furthermore, the material balance equation is more common in solving the variable production and pressure of shale gas wells issues, but it is only suitable for characterizing boundary flow. In this paper, a semi-analytical productivity prediction model of shale gas well for constant pressure was established and validated by the practical production data. Then the material balance pseudo time and linear superposition pseudo time were introduced respectively to modify the true pseudo time in the proposed productivity prediction model to demonstrate that the linear superposition pseudo time was proper to obtain the unknown fracture inversion parameters compared to material balance pseudo time during the variable pressure-production of actual shale gas wells. Finally, the Monte Carlo method in the IHS numerical software was adopted to analyze the impact of the fracture half-length uncertainty on the probability distribution of EUR, which showed that the P50 value is closer to the deterministic EUR value predicted by the analytical production prediction model. Research indicates that it is of certain theoretical reference to reduce the risk of production prediction during the production of shale gas wells and guide the optimization of development plans.