关键词: 廊固凹陷, 中浅层气类型, 后生生物气, 低熟气, 控藏因素

Abstract: Langgu Depression is a Cenozoic remaining basin with strong uplift and denudation in the late period. Numerous natural gas reservoirs of different types have been found in the middle and shallow layers (with the buried depth less than 3000 meters). Based on the source rock conditions, natural gas is divided into four types of origin. Taking into consideration the geological conditions of different structural positions, it is assumed that the origins of gas reservoirs in the middle and shallow layers are mainly Es3 biological gas reservoirs developed under degradation from methane into bacteria as well as Es3 and Es4 low-maturity gas reservoirs. Based on analysis of development process of the reservoirs of these two types, it is considered that biological gas reservoirs are controlled mainly by distribution of gas source rock and most abundant in the area close to the trap of gas source rock. Low-maturity gas reservoirs are controlled by hydrocarbon source rock and distributed in the surrounding area, migrating along the transportation formations composed of faults and sandstone. Gas is abundant mainly in the reverse faults