Different from oil properties, gas
properties (gas formation factor,
viscosity, and Z-factor, etc.) have nonlinear behaviors
with pressure changes. However, many scholars use the average pressure
or pseudopressure concept to simplify the phenomenon for easier solutions.
Gas flow in shales is believed to be a complex process with multiple
flow mechanisms including continuum flow, slip flow, diffusion, ad-desorption,
and the stress sensitivity of fractures (natural or induced) permeability
in multiscaled systems of nano- to macroporosity. Multistage hydraulic
fracturing not only creates the stimulated rock volume (SRV) to improve
production but also makes the flow in shales more complex. In this
work, a rectangular composite model for a multistage fractured horizontal
well (MFHW) with finite conductivity in shale gas considering the
multiple flow mechanisms and multi-nonlinearities is developed. Comparing
with the existing models for MFHW in shale, the model presented here
takes strong nonlinearity of gas properties, hydraulic fracture asymmetry,
fracturing efficiency, and SRV region into account, which is more
in line with field practice. Numerical simulation of fully implicit
control volume finite element (CVFE) based on unstructured 3D tetrahedral
mesh is proposed to obtain the production performance of MFHW. Sensitivity
analysis focuses on the effects of nonlinearity, Langmuir volume,
stress sensitivity, finite conductivity, and SRV type on the production
performance. The research and the numerical results obtained in this
work can provide theoretical guidance to efficient and scale development
for shale gas reservoir.
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