Hydrocarbon Accumulation Conditions and Exploration Direction of Paleogene Xiao’an Formation in Lingbao Sag, Sanmenxia Basin

The Sanmenxia Basin, which is subordinate to the Western Henan Uplift of the Southern North China Basin, is a small fault-depression basin dominated by the Cenozoic Erathem. Early studies indicated that this basin lacks the necessary geological conditions for source rock development, resulting in no breakthroughs in petroleum exploration and a generally low exploration intensity. Recently, significant breakthroughs have been made in Paleogene oil and gas exploration in the basin. Multiple exploration wells have obtained high-yield industrial oil flows, showing promising oil and gas exploration prospects. Based on field outcrop, seismic, and drilling data, as well as laboratory test results, this study systematically analyzes hydrocarbon accumulation conditions, summarizes the main controlling factors and accumulation models for oil and gas, and evaluates exploration potential. The research results show that high-quality saline lacustrine hydrocarbon source rocks are developed in the Podi Formation and the lower part of the Xiao’an Formation of the Paleogene in the basin, which is generally in a favorable stage of hydrocarbon generation and evolution. Deltaic sand bodies of the Xiao’an Formation serve as the dominant reservoirs, being mainly medium-porosity and medium-permeability with favorable physical properties. Oil and gas migrate and accumulate towards structural highs mainly along the composite fault-sandbody migration system. The hydrocarbon accumulation is dominated by the lower-generation and upper-accumulation assemblage, and the accumulation process is controlled by three key factors: source rock quality, reservoir development scales and trap effectiveness. This study establishes a hydrocarbon accumulation model summarized as multi-source hydrocarbon supply in deep sags of saline lacustrine facies, compound migration controlled by faults and sandbodies, and composite hydrocarbon accumulation in structural-lithologic traps. The Paleogene Xiao’an Formation is the main exploration interval for conventional oil and gas in the basin, and the Liulinhe Formation has important replacement exploration value. The deep strata also hold great exploration potential for unconventional shale oil and gas, as well as tight sandstone oil and gas. The Lingbao Basin possesses the optimal matching conditions of source-reservoir-cap assemblages and traps and is the key exploration area at present. The Yangping and Tongguan Sags have similar geological and hydrocarbon accumulation conditions to those of the Lingbao Sag, with broad scope for expanded exploration. Strengthening the depolyment of seismic exploration and drilling engineering and deepening research on hydrocarbon accumulation laws can drive strategic breakthroughs in conventional and unconventional oil and gas exploration in the Sanmenxia Basin.