Abstract
A fractal discrete fracture network based model was proposed for the gas production prediction from a fractured shale reservoir. Firstly, this model was established based on the fractal distribution of fracture length and a fractal permeability model of shale matrix which coupled the multiple flow mechanisms of slip flow, Knudsen diffusion, surface diffusion, and multilayer adsorption. Then, a numerical model was formulated with the governing equations of gas transport in both a shale matrix and fracture network system and the deformation equation of the fractured shale reservoir. Thirdly, this numerical model was solved within the platform of COMSOL Multiphysics (a finite element software) and verified through three fractal discrete fracture networks and the field data of gas production from two shale wells. Finally, the sensitivity analysis was conducted on fracture length fractal dimension, pore size distribution, and fracture permeability. This study found that cumulative gas production increases up to 113% when the fracture fractal length dimension increases from 1.5 to the critical value of 1.7. The gas production rate declines more rapidly for a larger fractal dimension (up to 1.7). Wider distribution of pore sizes (either bigger maximum pore size or smaller minimum pore size or both) can increase the matrix permeability and is beneficial to cumulative gas production. A linear relationship is observed between the fracture permeability and the cumulative gas production. Thus, the fracture permeability can significantly impact shale gas production.
Highlights
Horizontal well drilling and hydraulic fracturing are two key technologies to the economic production of unconventional oil and gas reservoirs [1,2]
In order to investigate the effects of a fractal discrete fracture network on gas production in a fractured shale reservoir, a fractal discrete fracture network model was established based on the fractal distribution of fracture length and incorporated into our coupling numerical simulation model
Fracture length fractal dimension is a key parameter to a fracture network
Summary
Horizontal well drilling and hydraulic fracturing are two key technologies to the economic production of unconventional oil and gas reservoirs [1,2]. In order to investigate the effects of a fractal discrete fracture network on gas production in a fractured shale reservoir, a fractal discrete fracture network model was established based on the fractal distribution of fracture length and incorporated into our coupling numerical simulation model. This simulation model further combines the complex gas transport mechanisms in shale matrix to describe the interaction of flow mechanisms and geometrical distribution in each fracture. Parametric analyses are performed to investigate the impacts of fracture length fractal dimension, pore size distribution, fracture permeability, and aperture on the well performance of this fractured shale reservoir
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