Numerical simulation of resistivity and saturation estimation of pore-type gas hydrate reservoirs in the permafrost region of the Qilian Mountains

Abstract

The pore-type hydrate reservoirs in the permafrost region of the Qilian Mountains (PRQM) have complex characteristics, including low porosity, low permeability, high shale content, and conductive minerals. Currently, the research on the electrical properties of these reservoirs still needs to be sufficiently in-depth, and there are limitations in well-logging evaluation methods. To fill in this gap, a conductivity model of pore-type gas hydrate reservoirs (GHRs) is established based on the pore-combination modeling theory to investigate the influencing factors of the resistivity characteristics of GHRs through numerical simulations. The comparison between the laboratory-measured resistivity of different hydrate saturations and the results of the calculated model shows good agreement, indicating the accuracy of the conductivity model in describing the electrical characteristics of GHRs in the PRQM. Compared to conductive minerals, the numerical simulation results indicate that the high shale content is the main reason for the decrease in resistivity of pore-type GHRs in the study area. The hydrate saturation evaluation of well DK-3 from 386.3 m to 393.6 m depth shows that the hydrate saturation ranges from 5.1% to 66.4%, with an average value of 44.0%. The identified hydrate interval using this model is consistent with the actual hydrate interval encountered during the drilling. This study, as an innovation, can help clarify the conductive mechanism of pore-type GHRs in the PRQM and provide more accurate parameters for evaluating gas hydrate resources in the study area.