Geochemical characteristics and enrichment regularity of bedrock reservoir in the central paleo-uplift, north songliao basin

The Central Paleo-Uplift is a key target for exploration in the deep layers of the Songliao Basin. Our study focused on the systematic analysis of the forming conditions and accumulation patterns of bedrock reservoirs. We conducted this analysis using data such as gas composition, isotopes, slices, and CT scans, while also considering factors such as source rock, hydrocarbon supply window, and transport channels. By analyzing these factors, we were able to gain insights into the geological processes that led to the formation of these reservoirs. Our findings reveal that the gas in the Central Paleo-Uplift is primarily coal-formed and highly mature. These gases originate from two main sources - the Xujiaweizi Fault Depression as the primary source, and the Gulong Fault Depression as the secondary source. We identified two types of gas reservoirs in the area, namely weathering reservoirs and inside bedrock reservoirs. The weathering reservoirs primarily contain gas trapped in erosion pores and fractures, while the inside bedrock reservoirs mainly contain gas in fractures. The Central Paleo-Uplift area is surrounded by favorable source rocks, with greater hydrocarbon supply windows on the east side compared to the west. The efficient transport channels have facilitated the accumulation of gas, while the presence of a steady mudstone cap has been advantageous for the preservation of gas reservoirs. The region contains various traps that are favorable for gas accumulation, with higher concentrations found at elevated positions. Our study identified three distinct accumulation patterns in the north, middle, and south regions of the Central Paleo-Uplift. The Wangjiatun Bulge, Changde Bulge, and Zhaozhou Bulge are particularly promising areas for exploration in this region.