In this work, different stages of gas production in shale reservoirs are modelled. First, hydraulic fracturing is considered by injecting water at high pressures to crack the formation and increase the flow capacity of the reservoir. During the fluid injection, rock properties are modified and water appears in the stimulated area. Then, these changes can be detected through seismic monitoring. Finally, once the fracking stage is completed, the simulation of gas production begins. The simultaneous gas–water flow in the injection and production stages is modelled using the Black-Oil formulation. Furthermore, a fracture criterion is applied under the hypothesis of constant temperature and constant stress field in this first analysis of the problem. The numerical simulations allow us to analyse the propagation of the fracture and the behaviour of the pore pressure and water saturation in the stimulated area. The advance of the fracturing fluid is delayed in relation to the breakdown of the rock. Besides, the presence of new fractures is detected by applying a poroviscoelastic wave propagation simulator that considers mesoscopic losses induced by heterogeneities in rock and fluids. After the fracture network is created, the injection well becomes a producer, allowing the extraction of gas and the flowback of the injected fluid. The simulated gas flow rates are compared with those obtained by a simplified single-phase analytical solution used for practical applications, achieving optimum matching results.

中文翻译：

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页岩气藏水力压裂与产气数值模拟

在这项工作中，对页岩储层天然气生产的不同阶段进行了建模。首先，水力压裂考虑通过高压注入水来破裂地层并增加储层的流动能力。在流体注入过程中，岩石性质发生改变，受刺激区域出现水。然后，可以通过地震监测来检测这些变化。最后，一旦水力压裂阶段完成，天然气生产的模拟就开始了。使用黑油公式对注入和生产阶段的同步气水流进行建模。此外，在问题的第一次分析中，在恒定温度和恒定应力场的假设下应用了断裂准则。数值模拟使我们能够分析裂缝的扩展以及受刺激区域的孔隙压力和水饱和度的行为。压裂液的推进相对于岩石的破裂被延迟。此外，通过应用多孔粘弹性波传播模拟器来检测新裂缝的存在，该模拟器考虑了岩石和流体中的不均匀性引起的细观损失。裂缝网络形成后，注入井成为生产井，允许提取气体和注入流体回流。将模拟的气体流量与实际应用中使用的简化单相解析解得到的流量进行比较，达到最佳匹配结果。