Studies On The Mechanism And Mode Of Deep Oil And Gas Accumulation In Wenliu Area Of Dongpu Depression

Based on summarizing the research of predecessors, the mechanism and mode of deepoil and gas accumulation in Wenliu area of Dongpu depression are investigated in this paperthrough the new theories and methods of Petroleum Geology, Reservoir Geochemistry,Structural Geology, and the technique of fluid inclusion analysis.A systematic research has been conducted about the characteristics of the deep reservoirsin Wenliu area. Vertically, the deep oil is mainly distributed in middle Sha3Member, and thedeep gas is mainly in middle Sha3Member, followed by Sha4Member. In two dimensions,the deep oil and gas are largely distributed in the Wendong garben zone, followed by theWendong rolling anticline zone and Wenzhong horst zone. The deep oil possesses the traits oflow density, low viscosity, low in sulfur and high freezing point. There are three kinds ofnatural gas in Wenliu area, gas from oil, gas from coal meatures and their mixture.The characteristics of source rocks and their thermal evolution history in Wenliu areahave been researched. Laterally, the source rock of Qianliyuan sag is better than that ofLiutun-Haitongji sag, and the source rock of lower Sha3Member ranks first in vertical layers.The coal-measure source rock of Taiyuan Formation is the best of theCarbonniferous-Permian, followed by Shanxi Formation and Benxi Formation. The kerogenin shaly source rock of middle and lower Sha3Member is mainly type II1, followed by typeII2. As for the coal-measure source rock of the Carbonniferous-Permian, the dominant kind ofkorogen is type III. The main part of Wenliu area is shallowly buried, with a low maturity. Insags, the source rock of middle Sha3Member is in the period of overmaturity and that oflower Sha3Member is of high-over maturity. The source rock of Carbonniferous-Permian hadreached post-maturity by the end of Paleogene.The process of deep oil and gas accumulation is synthetically researched and theaccumulation modes are established. Around the sags, deep oil and gas migrate from the sagsto the slope zone, from the south to the north, and accumute in the higher parts. The gas fromcoal in Wenliu area laterally migrates to the east and west from the filling point which is themeeting-point between Wendong Fault and the reservoir of Sha4Member. The deep oil andgas in the sags is two-stage accumulated, their relevant geological periods are late Eocene and late Nm Formation to nowadays. In the sags, the more deeply buried of the reservoir, the morecomplicated of the hydrocarbon filing periods. There is only one hydrocarbon filing period inWen23gas field, the relevant geological period is late Eocene. According to the dominantfactors of different kinds of deep reservoirs in Wenliu area, there are two kinds of deep oilaccumulation mode, one is of native source, two hydrocarbon filling periods, with the shapeof一controled by pressure, the other is of and the shape of exotic source, one hydrocarbonfiling period, with the shape of Z controled by fault.