Abstract: Shallow gas resources are widely distributed and have a broad prospect for exploration and development. In view of unclear understanding of shallow gas distribution in the Changchunling South Block, by taking the shallow-buried reservoir at the fourth member of Quantou Formation as the target formation, main controlling factor is specified by analyzing the reservoir forming conditions so as to obtain the controlling effect of sedimentary microfacies and fault on gas reservoir formation. The study results show that the gas source in the research area is mainly derived from the associated gas of crude oil generated by the hydrocarbon source rock at the first member of Qingshankou Formation. The reservoir is the fluvial facies deposition with thick channel sand body and good physical property, which is conducive to shallow gas enrichment. The reservoir sand bodies in fault structure and incline provide good vertical and lateral migration channels for shallow gas. The research area has an anticlinal shape, which is cut by three groups of faults in North-South, NW and a few NE strikes, and the structural trap conditions are good. Meanwhile, the hydrocarbon source rock at the first member of Qingshankou Formation is the regional cap rock with large thickness. The fault stops its activity at the late period of the Mingshui Formation and the preservation condition is good. Sedimentary microfacies and faults are the main controlling factors of shallow gas accumulation in the research area, so fault-lithologic gas reservoirs should be mainly sought, and the anticline uplift zone in the eastern part of the research area is a favorable exploration area. The research results point out a favorable direction for further exploration of this block.

Key words: shallow gas, reservoir forming conditions, main controlling factor, fourth member of Quantou Formation, Changchunling anticlinal zone