Numerical simulation for effect of discrete fracture network on shale gas productivity of horizontal well
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摘要: 页岩作为典型的非常规储层，基质孔隙小，渗透率极低，水平井多级水力压裂为其商业开发的主要手段。准确模拟页岩气产能，应同时考虑水力裂隙和天然裂隙的渗流。基于离散裂隙模型和等效连续模型建立页岩气渗流数学模型，利用有限元分析方法进行数值求解，研究不同走向裂隙组对页岩气井产能的影响。研究认为，页岩基质为气体的生产提供了主要气源，天然裂隙作为渗流的主要通道，将气体输送到水力裂缝，进而到达井筒。模拟结果表征，离散裂隙的渗流特征对于页岩气井的产能有重要影响。根据页岩储层的天然裂隙走向，可以优化相应的水平井方位。对于二维离散裂隙网络模型，水平井沿着2个裂隙组夹角的平分线更有利于生产。Abstract: As a typical unconventional reservoir, shale gas reservoirs have well-developed natural micro-fractures, in which the pores of matrix are small and the permeability is extremely low. Multi-staged hydraulic fracturing for horizontal well has become a key technology for commercial development. Therefore, in order to accurately simulate the shale gas production, hydraulic fractures and natural fractures should be considered simultaneously. In this paper, the mathematic model is established based on discrete fracture model (DFM) and equivalent continuum model (ECM). The model is solved by Finite Element Method (FEM). According to the model, the effect of different fracture sets with different fracture orientation is investigated. The results show that matrix provides main gas resource for gas production and natural fracture as main passage undertakes a task of transporting gas into hydraulic fracture, and then to wellbore. The characteristic of gas flow in discrete fracture network has an important impact on gas production. According to orientation of natural fracture, corresponding horizontal wellbore azimuth can be optimized. For 2D discrete fracture model, the horizontal well along the angle bisector of two fracture groups is more advantageous to gas production.
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