The Southern China Jiangnan—Xuefeng Structural Belt: Thrust Nappe Structural System and the Effect on Oil and Gas Resources

The complexity of the structural geology in Southern China presents significant challenges and risks to oil and gas exploration in the region. A key focus in recent years has been how to achieve breakthroughs in oil and gas exploration within these complex structures. Increasing geological evidence from surface structural mapping, geophysics, and drilling points to the possibility of buried marine Mesozoic and Paleozoic "shadow basins" beneath the nappes of the Jiangnan—Xuefeng Structural Belt. An analysis of the ancient oil reservoirs and remaining oil and gas fields along the northern edge of the Jiangnan—Xuefeng Structural Belt reveals that although the thrust nappe structures have exposed some Paleozoic strata at the surface, thereby disrupting oil and gas reservoirs, the nappe bodies (metamorphic rock cover areas) may effectively shield the underlying marine Paleozoic strata, preventing the escape of oil and gas. The analysis indicates that the main source of oil and gas is from three sets of high-quality Paleozoic source rocks, with the final period of hydrocarbon accumulation occurring in the late Yanshanian phase, coinciding with the final formation phase of the Jiangnan—Xuefeng Structural Belt. The activity of the thrust nappe structures also facilitates the formation of regional unconformities, creating high-quality reservoirs and structural traps, thus offering excellent spatial and temporal matching of source, reservoir, and cap rocks for secondary hydrocarbon accumulation, favorable for the formation of thrust nappe type oil and gas reservoirs. These geological elements also benefit the enrichment and preservation of Paleozoic marine shale gas under the cover of thrust structures, leading to a new approach in exploring both conventional natural gas and shale gas within a single well in the Jiangnan—Xuefeng Structural Belt.