基于非线性效应的页岩气产能预测模型

A productivity prediction model of shale gas wellbased on gas nonlinear effects

页岩气产出过程中非线性效应复杂,为产能的精确描述带来了较大困难,如今多数页岩气产能预测模型对气体跨尺度产出过程中的非线性效应认识不全面,导致气井产能预测结果不准确和生产动态规律分析存在误差。基于常规五区复合线性流模型,完善了模型中的气体综合非线性效应,建立了改进的复合线性流模型并获取了产能半解析解,进而验证了模型的可靠性,最后开展了气井生产动态规律实例分析。研究结果表明:考虑气体产出过程中对非线性效应的认识越完善,模型计算精度越高;吸附气是气井生产中后期长期稳产的关键组成部分,年吸附贡献率可超过50%,当地层压力降至临界解吸压力以下时,吸附气储量动用程度明显升高,单位压降下的累产气量明显上升,最终吸附气占比可达20%以上。研究成果可为准确评价页岩气储层动用效果及提高气藏动用率、最终气体采出程度提供一定的理论借鉴。

The complex nonlinear effects in the production process of shale gas wells have brought great difficulties to the accuracy of productivity evaluation.Nowadays,the nonlinear effects of the multi-scaled gas production process can be considered incomplete in most shale gas production prediction models,resulting in the inaccuracy of the production prediction of gas wells and errors in the dynamic production analysis of gas wells.Based on the conventional five-zone composite linear flow model,the comprehensive gas nonlinear effects were upgraded and an improved compound linear flow model was established in the paper.Subsequently,a semi-analytical solution of the proposed production model was obtained to verify the reliability of the model with practical production data.Ultimately,the gas well dynamic production analysis was developed.The research results show that:1)the more complete the various nonlinear effects in the gas production process,the more accurate the production prediction value and the greater the calculation accuracy;2)Adsorbed gas is a key component of shale gas wells long-term stable production,with an annual adsorption contribution rate exceeding 50%.When the pressure drops below the critical desorption pressure,the utilization of the adsorbed gas reserves will increase significantly,and the cumulative gas production under unit pressure drop will increase significantly.The final adsorbed gas volume will account for more than 20%in the cumulative gas production composition.The research results of this paper provide some theoretical reference for the accurate evaluation of shale gas reservoir utilization effect and the improvement of gas reservoir utilization rate and final gas recovery degree.