Abstract
Producing gas from shale strata has become an increasingly important factor to secure energy over recent years for the considerable volume of natural gas stored. Unlike conventional gas reservoirs, gas transport in shale reservoirs is a complex process. In the organic nano pores, slippage effect, gas diffusion along the wall, viscous flow due to pressure gradient, and desorption from Kerogen coexist; while in the micro fractures, there exist viscous flow and slippage. Hydraulic fracturing is commonly used to enhance the recovery from these ultra-tight gas reservoirs. It is important to clearly understand the effect of known mechanisms on shale gas reservoir performance. This article presents the pressure transient analysis (PTA) and rate decline analysis (RDA) on the hydraulic fractured vertical wells with finite conductivity in shale gas reservoirs considering multiple flow mechanisms including desorption, diffusive flow, Darcy flow and stress sensitivity. The PTA and RDA models were established firstly. Then, the source function, Laplace transform, and the numerical discrete methods were employed to solve the mathematical model. At last the type curves were plotted and different flow regimes were identified. The sensitivity of adsorption coefficient, storage capacity ratio, inter-porosity flow coefficient, fracture conductivity, fracture skin factor, and stress sensitivity were analyzed. This work is important to understand the transient pressure and rate decline behaviors of hydraulic fractured vertical wells with finite conductivity in shale gas reservoirs.
Highlights
With the growing shortage of domestic and foreign energy industry, producing gas from shale gas reservoirs is currently received great attention due to their potential to supply the entire world with sufficient energy for the decades to come (Wang and Krupnick 2013)
A shale gas reservoir is characterized as an organic-rich deposition with extremely low matrix permeability and clusters of mineral-filled ‘‘natural’’ fractures
In this paper, based on shale gas flow mechanisms, such as desorption, diffusion, and flow in the fractures, the mathematical model which considers the effect of outer boundary effects for hydraulic fractured vertical wells with finite conductivity has been constructed
Summary
With the growing shortage of domestic and foreign energy industry, producing gas from shale gas reservoirs is currently received great attention due to their potential to supply the entire world with sufficient energy for the decades to come (Wang and Krupnick 2013). It is necessary to study the pressure response for hydraulic fractured vertical wells, which is meaningful for effective shale gas production and deep understanding about gas flow mechanisms in unconventional shale reservoirs. In this paper, based on shale gas flow mechanisms, such as desorption, diffusion, and flow in the fractures, the mathematical model which considers the effect of outer boundary effects for hydraulic fractured vertical wells with finite conductivity has been constructed. This model considers Fick’s first law of diffusion, Langmuir isothermal adsorption (Yin 1991), and stress sensitivity of natural fracture.
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