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摘要
Accurate characterization of fracture zones induced by hydraulic pressure plays a very important role in production optimization, because it may help to understand the porosity and permeability of the reservoir. During microseismic monitoring, a common technique to delineate fractures is to locate microseismic events. However, due to low signal to noise ratio (SNR) and a limited number of microseismic events, the fracturing areas may not be well described by the spatial distribution of microseismic events. Additionally, except for the inherent anisotropy of shale, fractures often show preferred orientations, which may enhance anisotropy in the formations. Therefore, in this study we propose an approach to characterize the fractured zones by applying anisotropic reverse time migration (RTM) to microseismic waveform data. During hydraulic fracturing, microseismic waveforms may include scattered wavefield due to pre-existing fractures. We shall use the scattered wave-fields, P and S-wave codas, to image fractures. We analyze the feasibility of this method by testing numerical examples with various circumstances, such as configurations of event cluster and receiver positions, different uncertainties of event locations, velocity parameters, and noises, using downhole observation in 2D models. Synthetic tests demonstrate that we can directly image the nearby fracture zones with only a small number of microseismic events. Comparison between the isotropic and anisotropic migration results indicates that the anisotropy in the shale should not be ignored for imaging.
- 出版日期2018-8
- 单位中国科学技术大学
