页岩气藏SRV区域气体扩散与渗流耦合模型  

A coupling model for gas diffusion and seepage in SRV section of shale gas reservoirs

作　　者：高树生[1] 刘华勋[1] 叶礼友[1] 胡志明[1] 常进[1] 安卫国[1] Gao Shusheng Liu Huaxun Ye Liyou Hu Zhiming Chang Jin An Weiguo(Langfang Branch of PetroChina Exploration and Development Research Institute, Langfang, Hebei 065007, Chin)

机构地区：[1]中国石油勘探开发研究院廊坊分院

出　　处：《天然气工业》2017年第1期97-104,共8页Natural Gas Industry

基　　金：国家科技重大专项(编号:2011ZX05018);国家重点基础研究发展计划(973计划)项目(编号:2013CB228000)

摘　　要：页岩气藏有效开发的前提是储层大规模整体压裂形成有效流动的复杂缝网系统,即所谓的SRV区域,而准确描述该区域气体的流动规律是页岩气井产能评价与开发动态预测的基础。SRV区域由各种大小不同的基岩块与裂缝网络组成,二者的流动规律完全不同,基岩以扩散为主,裂缝以渗流为主。根据页岩储层基岩和裂缝的孔隙度、渗透率参数与吸附、扩散及渗流特征,分别建立二者的物质平衡方程,推导SRV区域基岩与裂缝中气体扩散与渗流的连续性方程;根据体积一致性的原理,为了方便计算,将体积压裂后的立方体基岩块简化为球体,结合球体截面拟稳态流动特征假设,运用Fick扩散定律和基质与裂缝中气体的密度函数推导出了气体的窜流方程,连续性方程与窜流方程的有机耦合可以有效描述SRV区域气体复杂的输运规律。研究结果表明,基岩扩散能力和体积压裂形成的基岩块大小(即压裂规模),共同决定着页岩气井的产能大小及稳产时间。实例计算结果表明,四川盆地长宁—威远地区A井区基岩扩散能力弱,约为10^(-5) cm^2/s,基岩块体积较大,等效球体半径约6.2 m,降低了气体由基岩向裂缝的窜流能力,因而大大影响了该气井的产能。结论认为,增加体积压裂规模、提高SRV区域内缝网密度是页岩气藏高效开发的重要手段。A prerequisite to effective shale gas development is a complicated fracture network generated by extensive and massive frac- turing, which is called SRV （stimulated reservoir volume） section. Accurate description of gas flow behavior in such section is fundamental for productivity evaluation and production performance prediction of shale gas wells. The SRV section is composed of bedrocks with varying sizes and fracture networks, which exhibit different flow behaviors - gas diffusion in bedrocks and gas seepage in fractures. According to the porosity and permeability and the adsorption, diffusion and seepage features of bedrocks and fractures in a shale gas res- ervoir, the material balance equations were built for bedrocks and fractures respectively and the continuity equations of gas diffusion and seepage in the SRV section were derived. For easy calculation, the post-frac bedrock cube was simplified to be a sphere in line with the principle of volume consistency. Under the assumption of quasi-steady flow behavior at the cross section of the sphere, the gas channel- ing equation was derived based on the Fick＇s laws of diffusion and the density function of gas in bedrocks and fractures. The continuity equation was coupled with the channeling equation to effectively characterize the complicated gas flow behavior in the SRV section. The study results show that the gas diffusivity in bedrocks and the volume of bedrocks formed by volume fracturing （or the scale of fractur- ing） jointly determine the productivity and stable production period of a shale gas well. As per the actual calculation for the well field A in Changning-Weiyuan block in the Sichuan Basin, the bedrock has low gas diffusivity-about 10 -5 cmZ/s and a large volume with equiv- alent sphere radius of 6.2 m, hindering the gas channeling from bedrocks to fractures and thereby reducing the productivity of the shale gas well. It is concluded that larger scale of volume fracturing and higher fracture density in the SRV zone are important guarantee

关 键 词：页岩气藏 SRV区域 基岩 裂缝网络 连续性方程 窜流方程 四川盆地 长宁—威远地区 

分 类 号：TE312[石油与天然气工程—油气田开发工程]