Abstract
A complex fracture network is generally generated during the hydraulic fracturing treatment in shale gas reservoirs. Numerous efforts have been made to model the flow behavior of such fracture networks. However, it is still challenging to predict the impacts of various gas transport mechanisms on well performance with arbitrary fracture geometry in a computationally efficient manner. We develop a robust and comprehensive model for real gas transport in shales with complex non-planar fracture network. Contributions of gas transport mechanisms and fracture complexity to well productivity and rate transient behavior are systematically analyzed. The major findings are: simple planar fracture can overestimate gas production than non-planar fracture due to less fracture interference. A “hump” that occurs in the transition period and formation linear flow with a slope less than 1/2 can infer the appearance of natural fractures. The sharpness of the “hump” can indicate the complexity and irregularity of the fracture networks. Gas flow mechanisms can extend the transition flow period. The gas desorption could make the “hump” more profound. The Knudsen diffusion and slippage effect play a dominant role in the later production time. Maximizing the fracture complexity through generating large connected networks is an effective way to increase shale gas production.
Highlights
Large-scale shale gas production began in 2000, when horizontal drilling and hydraulic fracturing techniques provided access to commercial volumes of shale gas
The method is based on the discrete fracture network simulation and the fracture flow is numerically solved by the method of finite difference method, which is related to gridding problem and computational cost
We develop a comprehensive and efficient semi-analytical model by incorporating the main shale gas flow mechanisms, including gas diffusion, gas desorption, gas slippage, and non-Darcy’s flow in the complex fracture network
Summary
Large-scale shale gas production began in 2000, when horizontal drilling and hydraulic fracturing techniques provided access to commercial volumes of shale gas. Yu et al (2015) developed a comprehensive semi-analytical model for gas transport in shale formation with complex fracture geometry[21]. We develop a comprehensive and efficient semi-analytical model by incorporating the main shale gas flow mechanisms, including gas diffusion, gas desorption, gas slippage, and non-Darcy’s flow in the complex fracture network. The effects of various gas flow mechanisms and fracture network complexities on well performance and rate transient behavior with the constraint of constant bottomhole pressure are studied systematically. To best of our knowledge, this work is the first study that presents the impacts of gas transport mechanisms on well performance and rate transient analysis in shale formations with the complex non-planar fracture network
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