Exploration breakthrough and hydrocarbon accumulation conditions of Mesozoic volcanic rocks in Bodong Low Uplift, Bohai Bay Basin, China

Abstract

The Mesozoic volcanic rocks of the Bodong Low Uplift in the Bohai Bay Basin have been studied and explored for years. In 2024, the LK7-A well drilled in this region tested high-yield oil and gas flows from volcanic weathered crust. These volcanic rocks need to be further investigated in terms of distribution patterns, conditions for forming high-quality reservoirs, and main factors controlling hydrocarbon accumulation. Based on the logging, geochemical and mineralogical data from wells newly drilled to the Mesozoic volcanic rocks in the basin, and high-resolution 3D seismic data, a comprehensive study was conducted for this area. The research findings are as follows. First, the volcanic rocks in the LK7-A structure are adakites with a large source area depth, and the deep and large faults have provided channels for the emplacement of intermediate-acidic volcanic rocks. Second, volcanic rock reservoirs are mainly distributed in tectonic breccias and intermediate-acidic lavas, and they are dominantly fractured-porous reservoirs, with high-porosity and low-permeability or medium-porosity and low-permeability. Third, the dominant lithologies/lithofacies is the basic condition for forming large-scale volcanic rock reservoirs. Structural fractures and late-stage strong weathering are crucial mechanisms for the formation scale of reservoirs in the Mesozoic volcanic rocks. Fourth, the Bodong Low Uplift exhibits strong hydrocarbon charging by two sags and overpressure mudstone capping, which are favorable for forming high-abundance oil and gas reservoirs. The Mesozoic volcanic buried hills in the study area reflect good trap geometry, providing favorable conditions for large-scale reservoir formation, and also excellent migration and accumulation conditions. Areas with long-term exposure of intermediate-acidic volcanic rocks, particularly in active structural regions, are the key targets for future exploration.