Marine CSEM 3D modeling with a downhole dipole source for natural gas hydrate production monitoring

Concerning the geological and environmental risks of marine natural gas hydrate (NGH) exploitation, the NGH production status needs to be monitored by detecting the changes in reservoir physical parameters. Since solid hydrate dissociation and free gas extraction contribute to the resistivity change...

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Bibliographic Details
Published in:Marine geophysical researches 2022-12, Vol.43 (4), p.43, Article 43
Main Authors: Liu, Ying, He, Tao, Li, Yuan, Zhang, Yi
Format: Article
Language:English
Subjects:
Dissociation
Earth and Environmental Science
Earth Sciences
Electric field
Electric fields
Environmental risk
Exploitation
Gas hydrates
Geophysics/Geodesy
Horizontal wells
Hydrates
Mathematical models
Monitoring
Natural gas
Numerical models
Ocean floor
Oceanography
Offshore Engineering
Original Research Paper
Reservoirs
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Summary:Concerning the geological and environmental risks of marine natural gas hydrate (NGH) exploitation, the NGH production status needs to be monitored by detecting the changes in reservoir physical parameters. Since solid hydrate dissociation and free gas extraction contribute to the resistivity changes of the reservoir layer, the marine controlled-source electromagnetic (CSEM) method could be potentially applied for NGH production monitoring. Considering the commercial exploitation of NGH in the future using horizontal wells in the South China Sea, we construct a 3D numerical model with three reservoir layers to investigate the feasibility of marine CSEM with a vertical downhole dipole source for NGH production monitoring. Based on the relative anomalies of modeled electric field responses at seafloor receivers before and after NGH production, it is found that (1) the transmitter should be optimally placed just below the hydrate layer and downward crossing the mixing and free-gas layers, (2) the absolute value and gradient of the relative anomaly reflect the range change of production zone, characterizing the monitoring performance of CSEM system, and (3) the marine CSEM is feasible for monitoring not only the long-term commercial NGH production but also the short-term trial production process as the case of China’s second NGH production test at Shenhu area. The study results suggest that the marine CSEM with a vertical source has good sensitivity for the electric field of short source-receiver offsets and an optimistic application prospect for the monitoring purpose of NGH productions.
ISSN:0025-3235
1573-0581
DOI:10.1007/s11001-022-09506-9