Abstract
Multi-stage fracturing horizontal well currently has been proved to be the most effective method to produce shale gas. This method can activate the natural fractures system defined as stimulated reservoir volume (SRV), the remaining region similarly is defined as un-stimulated reservoir volume (USRV). At present, no type curves have been developed for hydraulic fractured shale gas reservoirs in which the SRV zone has triple-porosity dual-depletion flow behavior and the USRV zone has double porosity flow behavior. In this paper, the SRV zone and USRV zone respectively are simplified as cubic triple-porosity and slab dual porosity media. We have established a new productivity model for multifractured horizontal well shale gas with Comprehensive consideration of desorption, diffusion, viscous flow, stress sensitivity and dual-depletion mechanism in matrix. The rate transient responses are inverted into real time space with stehfest numerical inversion algorithm. Type curves are plotted, and different flow regimes in shale gas reservoirs are identified. Effects of relevant parameters are analyzed as well. The whole flow period can be divided into 8 regimes: bilinear flow in SRV; pseudo elliptic flow; dual inter-porosity flow; transitional flow; linear flow in USRV; inter-porosity flow and boundary-dominated flow. The stress sensitivity basically has negative influence on the whole productivity period .The less the value of Langmuir volume and the lager the value of Langmuir pressure, the more lately the inter-porosity flow and boundary-dominated flow occurs. It in concluded that the USRV zone has positive influence on production and could not be ignored.
Highlights
Shale gas are typical unconventional reservoir due to its ultra-low permeability and porosity
The zone containing the main high-conductivity hydraulic fractures and large spacious network system both of which can effectively improve the wells performance is defined as stimulated reservoir volume (SRV), and the remaining zone which hardly influenced by the treatment of hydraulic fracturing is defined as un-stimulated reservoir volume (USRV) [2,3,4]
236 The Open Petroleum Engineering Journal, 2015, Volume 8 model with consideration of the impact of shale gas desorption and diffusion [15], the impact of USRV zone was neglected; Xu et al (2012) analyzed the effect of USRV zone on shale gas production, at the same time, the impact of desorption diffusion is considered as well [16]; Zhao et al (2013) proposed triple-porosity spherical flow model for the fractured infinite shale gas reservoirs which considered the impact of diffusion and desorption [17], they considered artificial fractures as infinite conductivity
Summary
Shale gas are typical unconventional reservoir due to its ultra-low permeability and porosity. 236 The Open Petroleum Engineering Journal, 2015, Volume 8 model with consideration of the impact of shale gas desorption and diffusion [15], the impact of USRV zone was neglected; Xu et al (2012) analyzed the effect of USRV zone on shale gas production, at the same time, the impact of desorption diffusion is considered as well [16]; Zhao et al (2013) proposed triple-porosity spherical flow model for the fractured infinite shale gas reservoirs which considered the impact of diffusion and desorption [17], they considered artificial fractures as infinite conductivity In terms of these naturally fractured reservoirs, the phenomenon of stress sensitivity is readily observed. This model compares with numerical simulation and exhibits good agreements
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