Abstract: A series of inherited structural traps with excellent reservoir formation conditions developed at a depth of >6 000 m in the Mahu Sag, surrounding Carboniferous system, and deep layers of the Lower Permian system. Through optimized selection, we chose the Da-1 Well anticline as the oil-gas exploration breakthrough point. The exploration of the Da-1 Well anticline Carboniferous structural trap might be the key to success in answering crucial questions such as whether a Carboniferous system can develop into an effective reservoir or what the formation patterns are for fluid phase traps and oil-gas reservoirs. Although a single well provides insufficient data based on the calibration of gravity-magnetic-electric data with drilling data, we consider the Da-1 Well anticline to be a developing basic volcanic weathering crust reservoir with relatively poor physical properties. The Da-1 Well anticline was predicted to be a gas reservoir based on the data on the evolutionary stages of the hydrocarbon source rock in the Mahu Area, seismic horizon velocity, and shallow well testing. Based on the structural evolution and hydrocarbon analysis, we consider the Da-1 Well anticline to be a side-of-source, multi-stage unconformity, lateral migration reservoir formation. After combining all factors, such as reservoir and fluid phase factors and reservoir-forming conditions and depth, the analyses confirm that the Da-1 Well anticline has advantageous conditions and high potential for reservoir formation, promising high-yielding gas flow and the exploration of a large gas field.

Key words: Carboniferous, fluid phase, reservoir formation pattern, volcanic rocks, weathering crust, Mahu Sag