Search

The shale gas productivity model based on shale gas nonlinear seepage mechanism is an effective way to reasonably predict productivity. The incomplete gas nonlinear effects considered in the current production prediction models can lead to inaccurate production prediction. Based on the conventional five-zone compound flow model, comprehensive gas nonlinearities were considered in the improved compound linear flow model proposed in the paper and a semianalytical solution for productivity was obtained. The reliability of the productivity model was verified by the field data, and then, the 20-year production performance analysis of the gas well was studied. Ultimately, the key influencing factors of the fracture control stage and matrix control stage have been analyzed. Research indicated the following: (1) the EUR predicted by the productivity model is higher than the EUR that the comprehensive nonlinear effects are not considered, which demonstrated that the various nonlinear effects cannot be neglected during the production prediction to ensure the greater calculation accuracy; (2) during the early production stage of shale reservoir, the adsorbed gas is basically not recovered, and the cumulative adsorption contribution rate does not exceed 10%. The final adsorption gas contribution rate is 23.28%, and the annual adsorption rate can exceed 50% in the 20th year, showing that free gas and adsorbed gas are, respectively, important sources of the early stage of production and long-term stable production; (3) the widely ranged three-dimensional fracturing reformation of shale reservoirs and reasonable bottom hole pressure in the later matrix development process should be implemented to increase the effective early production of the reservoir and ensure the earlier gas production process of the matrix development. The findings of this study can help for better ensuring the prediction accuracy of the estimated ultimate recovery and understanding the main influencing factors of the dynamic performance of gas wells so as to provide a theoretical reference for production optimization and development plan formulation of the shale gas reservoirs. [ABSTRACT FROM AUTHOR]

The shale gas productivity model based on shale gas nonlinear seepage mechanism is an effective way to reasonably predict productivity. The incomplete gas nonlinear effects considered in the current production prediction models can lead to inaccurate production prediction. Based on the conventional five-zone compound flow model, comprehensive gas nonlinearities were considered in the improved compound linear flow model proposed in the paper and a semianalytical solution for productivity was obtained. The reliability of the productivity model was verified by the field data, and then, the 20-year production performance analysis of the gas well was studied. Ultimately, the key influencing factors of the fracture control stage and matrix control stage have been analyzed. Research indicated the following: (1) the EUR predicted by the productivity model is higher than the EUR that the comprehensive nonlinear effects are not considered, which demonstrated that the various nonlinear effects cannot be neglected during the production prediction to ensure the greater calculation accuracy; (2) during the early production stage of shale reservoir, the adsorbed gas is basically not recovered, and the cumulative adsorption contribution rate does not exceed 10%. The final adsorption gas contribution rate is 23.28%, and the annual adsorption rate can exceed 50% in the 20th year, showing that free gas and adsorbed gas are, respectively, important sources of the early stage of production and long-term stable production; (3) the widely ranged three-dimensional fracturing reformation of shale reservoirs and reasonable bottom hole pressure in the later matrix development process should be implemented to increase the effective early production of the reservoir and ensure the earlier gas production process of the matrix development. The findings of this study can help for better ensuring the prediction accuracy of the estimated ultimate recovery and understanding the main influencing factors of the dynamic performance of gas wells so as to provide a theoretical reference for production optimization and development plan formulation of the shale gas reservoirs. [ABSTRACT FROM AUTHOR]

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. • The production model is proposed to characterize the variable production and variable pressure issues. • The linear superposition time is more suitable to characterize the dynamic performance of shale gas wells. • The model parameters inversion and probability distribution of EUR is persuasive to reduce the risk of production effect evaluation. • The P50 value is closer to the true prediction result of EUR value. [ABSTRACT FROM AUTHOR]