Abstract
In this study, we introduced multitransient electromagnetic (MTEM) method as an effective tool for shale gas exploration. We combined the uniaxial perfectly matched layer (UPML) equation with the first derivative diffusion equation to solve for a finite difference time domain (FDTD) UPML equation, which was discretized to form an algorithm for 3D modeling of earth impulse response and used in modeling MTEM response over 2D South China shale gas model. We started with stepwise demonstration of the UPML and the FDTD algorithm as an effective tool. Subsequently, quantitative study on the convergence of MTEM earth impulse response was performed using different grid setup over a uniform earth material. This illustrates that accurate results can be obtained for specified range of offset. Furthermore, synthetic responses were generated for a set of geological scenarios. Lastly, the FDTD algorithm was used to model the MTEM response over a 2D shale gas earth model from South China using a PRBS source. The obtained apparent resistivity section from the MTEM response showed a similar geological setup with the modeled 2D South China shale gas section. This study confirmed the competence of MTEM method as an effective tool for unconventional shale gas prospecting and exploitation.
Highlights
Shale gas as the natural gas that is found trapped within the shale formation has become an important source of natural gas in China and a major energy source in the rest of the world
According to Nie et al [4], the most favorable areas for shale gas accumulation and recovery are located in Sichuan Basin, Micangshan-Dabashan foreland and East Chongqing, West Hubei Province of Upper-Yangtze River, North Hubei Province of Middle-Yangtze River, and South
We determined its applicability in shale gas exploration, which is intended at mapping the unconventional source rocks and exploitation process in South China
Summary
Shale gas as the natural gas that is found trapped within the shale formation has become an important source of natural gas in China and a major energy source in the rest of the world. MTEM is a relatively new time domain method which gives a high-resolution result [28], continuous 2D view of the subsurface resistivity distribution across a section [29], 3D volume resistivity image to supplement high-resolution seismic data in decision-making, and risk reduction [28] and has the capability to help maximize recoverable reserves and CO2 sequestration process, via 4D survey monitoring of water, gas, and/or chemicals injected into reservoirs during enhanced recovery programs [30, 31] The comparison of both CSEM and MTEM methods by Anderson et al [28] shows that the latter, which is used for both land and marine study (including deep offshore study), has several advantages over CSEM method. The final exercise in this study established MTEM as an effective and efficient tool used in subsurface characterization for shale gas prospecting and exploitation via quick reconstruction of earth resistivity distribution
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