页岩气藏多重介质耦合流动模型

为准确掌握页岩气流动规律以及精准评价水力压裂效果, 需要建立页岩气藏多重介质耦合流动模型。为此，基于页岩气 藏干酪根、无机基质及裂缝物性特征，综合考虑微纳米尺度气体黏性滑脱、努森扩散、吸附解吸、表面扩散等运移规律，通过表观 渗透率来综合表征页岩气藏多尺度介质渗流机理。在此基础上，考虑储层压裂改造特征及跨尺度流体传质机理，建立页岩气藏多重 介质耦合流动模型，应用Laplace 变换和Stehfest 数值反演，得到了定产和定压情况下封闭边界单裂缝井底无因次拟压力和产量半解 析解。在模型正确性验证的基础上，结合矿场参数对模型进行实例分析。结果表明：①干酪根是页岩气藏重要的烃源介质，干酪根 含量每增加10%，对页岩气累积产量的贡献度增加12% 左右；②无机基质滑脱效应及努森扩散在对生产中期气体流速产生较大影响 的同时也增大了孔隙压力衰竭速度。基于所建流动模型研究了页岩气藏分段压裂水平井流动规律，结果表明：不考虑井筒存储及表 皮效应时，储层有线性流、双线性流、“双窜流”、无机基质稳态流、拟边界流、“三线性”流、封闭边界流7 个流动阶段。

A multi-media coupling flow model for shale gas reservoirs

It is necessary to establish a multi-media coupling flow model for shale gas reservoirs in order to understand the shale gas flowing rules and accurately evaluate the hydraulic fracturing effects. In this paper, migration rules were comprehensively investigated on the basis of kerogen, inorganic matrix and fracture physical properties of shale gas reservoirs, including nano-scale gas viscosity slippage, Knudsen diffusion, adsorption-desorption and surface diffusion. The multi-scale medium filtration mechanisms of shale gas reservoirs were characterized comprehensively by using the apparent permeability. Then, a multi-media coupling flow model for shale gas reservoirs was established considering the reservoir fracturing characteristics and cross-scale fluid mass transfer mechanisms. Based on Laplace transformation and Stehfest numerical inversion, the semi-analytical solutions of dimensionless pseudo-pressure and production at the bottom hole with closed boundary single fracture were calculated under constant production rate and pressure. Finally, a case study was made on the model by using field parameters after it was verified. It is shown that kerogen is an important hydrocarbon source medium for shale gas reservoirs and it contributes to the cumulative shale gas production increment of 12% if kerogen content rises by 10%. Inorganic matrix slippage effect and Knudsen diffusion have more effects on gas flow rate in the middle period of the production, and also increase the depletion rate of pore pressure. The flow rules of staged-fracturing horizontal wells in shale gas reservoirs were investigated by using this flow model. It is indicated that there are seven flow stages (i.e., linear flow, bilinear flow, “bi-cross flow”, inorganic matrix stable flow, pseudo boundary flow, “trilinear” flow and closed boundary flow) if wellbore storage and skin effect are not taken into consideration.