页岩气藏压裂动用程度及气体流动模拟研究

Study of a Simulation of Degree of Fracturing Production and Resulting Gas Flow in Shale Gas Reservoirs

  • 摘要: 页岩储层孔喉细小、渗透率低,水力压裂后形成主裂缝及诱导裂缝网络加剧了页岩气流动的复杂性。为了准确表征页岩气拟稳态渗流特征,提出了离散裂缝耦合多重连续介质系统数学表征方法,并针对储层裂缝分布形态,利用商业数值模拟器建立了考虑吸附/解吸的页岩气藏离散裂缝耦合多重连续介质数值模拟模型。模型中采用局部网格加密的方法描述离散裂缝网络,基于建立的多重连续介质系统数学方法表征压裂后形成的密集分布微小裂缝体系。利用建立的模型,系统分析了储层横向/纵向动用程度以及裂缝导流能力、裂缝半长、裂缝排布方式等裂缝参数对页岩气泄气面积和气井产能的影响。研究发现,增大储层改造体积能够大幅度提高页岩气单井产量,但同时应当考虑主裂缝与次裂缝网络的配置关系;当储层改造体积相同时,最大限度提高裂缝与井筒之间的连通程度是提高页岩气产量的必要条件。研究认为,上述研究结果对页岩气压裂改造设计具有一定的理论指导意义。

     

    Abstract: Due to small pore throats and low permeability of shale reservoirs,primary natural fractures and induced fracture networks hydraulic fracturing can dramatically aggravate the complexity of shale gas flow.We needed to accurately characterize the pseudo-steady seepage characteristics of shale gas.To do so,we proposed a mathematical characterization method using discrete fractures coupled with a multiple continuous media system.Taking into consideration the distribution of reservoir fractures,the commercial numerical simulator was used to establish the discrete fractures and to couple them with multiple continuous media took into consideration adsorption/desorption for shale gas reservoirs.The mathematical model incorporated a local grid encryption method to describe the discrete fracture network.Based on the established multi-continuum system mathematical method,it was possible to model induced fractures within the natural fractures,including densely distributed micro-crack system that formed after fracturing.By using the established model,it was possible to systematically analyze the effects of fracture parameters,such as lateral/longitudinal mobilization of reservoirs,fracture conductivity,fracture half-length,and fracture arrangement on shale gas drainage area and gas well productivity.Studies revealed that increasing the reservoir stimulation volume could significantly increase shale gas production per well.Above all,the configuration relationship between the main fracture and the secondary fracture network should not be ignored.The model demonstrated that under the same reservoir stimulation volume,the connectivity between the fracture and wellbore was a necessary condition for increasing shale gas production,and it should be maximized.Studies suggested that the new modeling technique is effective and that it can be used as a guide when designing shale gas fracturing stimulation.

     

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