Shale-gas well test analysis and evaluation after hydraulic fracturing by stimulated reservoir volume (SRV)

Abstract

At present, there are a lack of mature and accurate analysis methods for post-frac evaluation and productivity prediction of shale reservoirs after hydraulic fracturing by stimulated reservoir volume (SRV). And the application is limited if only one method is used for evaluation, such as micro-seismic monitoring and pump-off drawdown test. In this paper, the fracture network morphology formed by SRV and the expected stimulation results were analyzed. Then, the stimulation results of SRV in shale gas wells were presented by sections by “semi-length of shorter effective fracture + higher effective permeability in SRV” method, so as to stress the forms of main fracture channels near the wells. The radial flow inside the SRV cannot be described by using the traditional multiple, long and straight areal fracture model. This problem was solved after the stimulation results of SRV which was cut and broken by complicated, dense fracture systems moderately far from the wells were described equivalently based on the concept of average effective permeability. As a result, the improvement effects of seepage capacity inside the SRV contributed by hydraulic fracturing were evaluated more rationally, and the productivity was predicted more accurately and stably. This method was applied in a shale-gas horizontal well fracturing in Weiyuan block, Sichuan Basin. It is shown that the seepage performance of fracture networks generated by SRV fracturing is quite different from that of surface source fractures, and it is more similar to the point source flow with perforations or near-well main fracture channels as the center. Besides, well test performance presents the characteristics of radial or pseudo-radial flow instead of linear flow. And the SRV can also be characterized by using the shorter main fracture length and the effective permeability which is several orders of magnitude higher than that of shale matrix.