Integration of Electromagnetic Geophysics Forward Simulation in Coupled Flow and Geomechanics for Monitoring a Gas Hydrate Deposit Located in the Ulleung Basin, East Sea, Korea

Abstract

We investigate the feasibility of electromagnetic (EM) geophysics methods to detect the dissociation of gas hydrate specifically from a gas hydrate deposit located in the Ulleung Basin, East Sea, Korea via an integrated flow-geomechanics-EM geophysics simulation. To this end, coupled flow and geomechanics simulation is first performed with the multiple porosity model employed, where a mixed formulation with the finite volume (FV) and finite element (FE) methods are taken for the flow and geomechanics, respectively. From the saturation and porosity fields obtained from the coupled flow and geomechanics, the electrical conductivity model is established for the EM simulation. Solving the partial differential equation of electrical diffusion which is linearized using the 3D finite element method (FEM), the EM fields are then computed. For numerical experiments, particularly two approaches in the configuration for the EM methods are compared in this contribution: the surface-to-surface and the surface-to-borehole methods. When the surface-to-surface EM method is employed, the EM is found to be less sensitive, implying low detectability. Especially for the short term of production, the low detectability is attributed to the similarity of electrical resistivity between the dissociated gas (CH4) and hydrate as well as the specific dissociation pattern within the intercalated composites of the field. On the other hand, when the surface-to-borehole EM method is employed, its sensitivity to capture the produced gas flow is improved, confirming its detectability in monitoring gas flow. Hence, the EM geophysics simulation integrated with coupled flow and geomechanics can be a potential tool for monitoring gas hydrate deposits.

Review and Outlook on Fracturing Technology and Mechanism of Hydrate-Bearing Sediments

“…Therefore, how to maintain the structural stability of sediments and provide stable seepage channels during hydrate decomposition is an application problem that needs to be solved in hydrate exploitation. 27 As a mature reservoir modification technology, hydraulic fracturing has been applied to low-permeability oil and gas reservoirs and the extraction of gas shale, oil shale, and hot dry rock, which can effectively increase the production of oil and gas wells and promote the further increase of hydrate production capacity. 28−32 Fracturing produces artificial fractures in the formation, as shown in Figure 1, which can effectively expand the pressure wave range at the bottom of the well; at the same time, the fracture after fracturing is easy to close, and after the fracture is filled with proppant, the artificial fracture formed has sufficient conductivity, 33 which can be used as an effective seepage channel for fluids to enhance the conductivity of the formation and to expand the area of oil and gas pumping through the high conductivity channel of the borehole.…”