Abstract
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.
Highlights
Nowadays, shale gas has occupied an important strategic position in the energy structure of worldwide natural gas production for its rich reserves and energy efficiency [1]
Productivity model based on shale gas complex flow mechanism is an Geofluids effective approach to reasonably analyze the production performance of shale gas wells, which can avoid the limitations of shale gas production empirical equations and is of theoretical significance and application value to formulate shale reservoir fracturing design plans and guide the exploration and development of shale gas reservoirs
(1) Based on the conventional five-zone composite flow model, the supercritical adsorption, diffusion, slippage stress sensitivity, and the gas high-pressure physical property are comprehensively considered in the improved flow model, which makes up for the lack of consideration of gas nonlinear effects in previous productivity models
Summary
Shale gas has occupied an important strategic position in the energy structure of worldwide natural gas production for its rich reserves and energy efficiency [1]. Productivity model based on shale gas complex flow mechanism is an Geofluids effective approach to reasonably analyze the production performance of shale gas wells, which can avoid the limitations of shale gas production empirical equations and is of theoretical significance and application value to formulate shale reservoir fracturing design plans and guide the exploration and development of shale gas reservoirs. In this paper, considering the lack of the nonlinear factors of the existing production model, the workflow is developed as follows: first, the nonlinearity of real-gas physical properties, high-pressure desorption of adsorbed gas, the non-Darcy flow mechanism such as slippage effect and diffusion, and the stress sensitivity of the secondary fracture network are comprehensively considered in the production prediction model. The key production influence factors of gas wells have been clarified, and specific guidelines for production optimization have been put forward, which is of certain theoretical reference to increase gas reservoir production rate and final gas recovery
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