Abstract
Shale gas reservoirs (SGR) have been a central supply of carbon hydrogen energy consumption and hence widely produced with the assistance of advanced hydraulic fracturing technologies. On the one hand, due to the inherent ultralow permeability and porosity, there is stress sensitivity in the reservoirs generally. On the other hand, hydraulic fractures and the stimulated reservoir volume (SRV) generated by the massive hydraulic fracturing operation have contrast properties with the original reservoirs. These two phenomena pose huge challenges in SGR transient pressure analysis. Limited works have been done to take the stress sensitivity and spatially varying permeability of the SRV zone into consideration simultaneously. This paper first idealizes the SGR to be four linear composite regions. What is more, the SRV zone is further divided into subsections on the basis of nonuniform distribution of proppant within the SRV zone which easily yields spatially varying permeability away from the main hydraulic fracture. By means of perturbation transformation and Laplace transformation, an analytical multilinear flow model (MLFM) is obtained and validated as a comparison with the previous models. The flow regimes are identified, and the sensitivity analysis of critical parameters is conducted to further understand the transient pressure behaviors. The research results provided by this work are of significance for an effective recovery of SGR resources.
Highlights
Due to extremely low permeability and porosity of shale gas reservoir (SGR), multistage hydraulic fracturing has become an integral tool to improve the gas recovery
The zone containing the main high-conductivity hydraulic fractures and large spatial network system which can effectively improve well performance is defined as stimulated reservoir volume (SRV), and the remaining zone which is hardly influenced by the treatment of hydraulic fracturing is defined as USRV (Mayerhofer et al 2006, [2, 3])
By means of perturbation transformation and Laplace transformation, we proposed a new analytical multilinear flow model to systematically investigate the effects of stress sensitivity in SGR
Summary
Due to extremely low permeability and porosity of shale gas reservoir (SGR), multistage hydraulic fracturing has become an integral tool to improve the gas recovery. Brown et al [12] presented an analytical trilinear flow model that incorporates transient fluid transfer from the matrix to the fracture to simulate the pressure transient and production behavior of fractured horizontal wells in unconventional reservoirs. Those proposed analytical models lack the ability to explicitly consider the medium conductivity secondary fracture, which absolutely induces certain errors to some degree. Given the stress sensitivity effect of fractures and reservoirs, Wang et al [19] established a semianalytical model suitable to study transient flow behaviors of a multistage fractured horizontal well with complex fracture networks without considering the property contrast between the stimulated zone and the unstimulated zone. Corresponding solutions can be useful for fracture design and well test interpretation in field practice
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