Quantitative evaluation of lateral sealing of faults in metamorphic rocks: A case study of Bohai Bay Basin in China

The Archean buried-hill metamorphic reservoirs in the Bohai Bay Basin are examples of metamorphic rocks having faults with diverse strikes as a consequence of multi-phase tectonic evolution. For faults in metamorphic rocks, no method that accounts for the properties of metamorphic rocks exists for evaluating fault sealing capacity. To elucidate the mechanisms controlling sealing capacity, our study pioneers a novel methodology termed the Mylonite Gouge Ratio (MGR) method. This method integrates neutron density log responses, petrophysical characteristics, and corresponding depth-specific rock thin-section analyses to assess lateral fault sealing capacity. Application of this set of rules and procedures to metamorphic faults in the basin's Archean strata reveals two critical findings: spatially, the Block X exhibits elevated MGR values indicative of superior sealing efficiency; temporally, Yanshanian NE-trending faults demonstrate enhanced sealing capacity compared to Himalayan EW-trending counterparts, with pre-Yanshanian and syn-Yanshanian tectonic activities facilitating paleo-fluid migration while current sealing conditions favor hydrocarbon preservation. The new method provides a tailored framework for evaluating fault sealing in metamorphic rocks, where conventional methods designed for sedimentary sequences are often inapplicable. This study establishes a new theoretical model for fault-sealing analysis in complex metamorphic reservoirs, with implications for deep hydrocarbon exploration and development.