摘要
Low thermal evolution degree of gas and connected fracture network are key features in the continental shale gas reservoirs.When the pressure decreases lower than the dew point pressure,gas condensate diminishes the mobility of subsurface fluid forms in the near well region,which further reduces the productivity and final recovery factor in addition to the low connected fracture network.This work is motivated to investigate the application of gas injection,proven to be a feasible technique in conventional/marine-shale gas condensate reservoirs,in continental shale gas condensate reservoirs.We apply a compositional model to investigate the mechanism of gas injection treatment taking a continental shale gas condensate reservoir in the Fuxing area,Sichuan Basin,China as an example.The results demonstrate that for the removal of gas condensate during CO_(2)injection,re-vaporization plays the main mechanism through two processes including pressurization and development of miscibility,while the former is overwhelming.Considering the variation trend of the total volume of gas condensate,we divide the whole injection process into four and six stages in the single fracture model and fracture network model,respectively,and reason the trend with respect to phase behavior and flow pattern.A sensitive study on the injected gas type indicates that the sorting of the gas injection performance to remove gas condensate produced gas followed by CH4,and followed by CO_(2).Finally,we investigate the performance of cyclic produced-gas injection and optimize the injection scheme.This work provides technical and theoretical support for the development of continental shale gas reservoirs.
陆相页岩凝析气藏的主要特征包括热演化程度低和裂缝网络连通性差.当压力衰减至露点压力时,近井地带开始析出凝析油,导致地层流体流度降低.与裂缝网络连通性差相似,该行为会降低产能和最终采收率.注气解除反凝析已经在常规凝析气藏和海相页岩凝析气藏开发中取得良好效果,本文旨在探讨其在陆相页岩凝析气藏中的应用.以中国四川盆地复兴区块某陆相页岩凝析气藏为例,采用组分模型研究注气解除反凝析机理.结果显示,注CO_(2)消除凝析油的主要机理是再气化,通过加压和混相实现,前者占主导地位.根据地层中凝析油总量变化趋势对注入过程进行阶段划分,单裂缝模型可以划分为4个阶段,裂缝网络模型可以划分为6个阶段.针对每个阶段,结合相态和流动模式详细分析了变化趋势及其原因.此外,注气介质敏感性分析结果表明,注产出气的解除反凝析效果优于甲烷,优于CO_(2).最后研究了循环注产出气的效果,并对注气策略进行了优化.本文工作为陆相页岩凝析气藏开发提供了理论和技术支持.
基金
supported by the Sinopec Key Laboratory of Shale Oil and Gas Drilling,Completion and Fracturing(Grant No.35800000-22-ZC0613-0023)
Beijing Municipal Natural Science Foundation(Grant No.2232073)
the Sinopec Science and Technology Department(Grant Nos.P21078-8 and P22005).
