The Study On Deep Structure And The Controlling Factor For Gas Accumulation In Changde Gas Field

The deep gas reservoir in Daqing oil field is consist of Xushen, Changde and Shengping gas field, and has been built 14×108m3/year capacity. During "Twelfth Five Year Plan" period, The gas production in Daqing oil field will reach at 50×108m3/year, and Changde gas field is one of the most important development block. In order to develop the reserves of Changde gas fieldand, provide technical support for the further exploration and development, it is necessary to study the deep structure and the controlling factor of gas accumulation in Changde gas field.Based on the fine interpretation of 3-D seismic data, the paper suggests that there are three sets of fault systems in Changde gas field, and they are the W-S trending normal fault system developed during the early Cretaceous rifting period, the N-S trending normal fault system developed during the period of the Qingshankou formation and the normal fault system developed during Cenozoic. During the early Cretaceous, the EW trending normal faults controlled the deposition and the development of faulted depression.The N-S trending normal fault system developed during the period of Qingshankou formation, shows the characteristics of weak growth fault,and has obvious effect on the deposition.The deep gas reservoir of Changde gas field is constituted of Changde gas reservoir and Eastern Changde gas reservoir, in which they have significant differences in terms of the gas composition, distribution, carbon isotope characteristics and gas reservoir types. For the origin of natural gas, a considerable part of natural gas in Changde gas reservoir is inorganic gas derived from deep earth, but Eastern Changde gas reservoir is mainly of coal source organic gas from the hydrocarbon source rocks in Xujiaweizi fault depression.On the basis of previous studies, combined with a variety of test and analysis of 13 wells about Changde gas field, the author puts forward the accumulation model about Changde gas field, they are the unconformity+weathering crust of basement rock, the unconformity or sandy body+fault+ palaeo uplift, the fracture+volcanic rock, the trap of sandy body+stratigraphic overlap.