Research On Cap Sealing Ability And Its Seal History In Xujiaweizi Fault Depression

According to the distribution layer of natural gas in Xujiaweizi fault depression, there are three sets of reservoir-cap combination, but the top of K1yc volcanic rock/ mudstone cap rock and shale cap rock in K1d is the main cap rock. The former is cover of volcanic gas reservoirs in K1yc1 only distributed in the southernof Xujiaweizi fault depression; The latter is cover of conglomerate gas reservoirs in K1yc4 and volcanic gas reservoirs in K1yc3, distributed in the whole depression. First, the use of lithology and well logs and other information on the developmental characteristics of a single well cover, the results show that the cover at the top of K1yc1 is mudstone, medium thickness, and its displacement pressure is greater than the displacement pressure of the reservoir, With a sealing ability to gas of K1yc1, and the cap rock lithology of K1d2 is mudstone, fine sandstone, with small displacement pressure.Flat cap thickness distribution of natural gas showed that the thickness high-value of cover in K1d2 located in the south of Dashen gas reservoir, the eastern Xushen 1 gas reservoir, the south of Xushen 21 and Zhaoshen1 gas reservoir, the cover thickness decreased from central to the surrounding cover. Thickness of high-value point of in cover of K1yc1 located in the north of Xudong gas reservoir, the northeast area of Xujiaweizi fault depression, the cover thickness gradually thinning to the south and west. Second, the micro-sealing ability of the caps in K1yc1 and K1d2 are different, the mudstone cap rock of K1d2 is regional cap rock, displacement pressure is greater, the sealing ability is stronger than K1yc1, the local cap rock. Meanwhile, it established Xujiaweizi caprock level of evaluation criteria through the relationship of 21 gas reservoirs displacement pressure and the abundance, the evaluation showed that mudstone caprock in K1d2 and volcanic rock /shale caprock in the top of K1yc1 are mainly the rigion of high sealing ability and high abundance of gas reserves, the area of good sealing ability and low abundance of gas reserves are relatively small. Finally, to further the cap sealing ability to the natural gas in the deposition process, we restored the sealing ability of caprock history, the results show that the mudstone caprock in K1d2 and volcanic rock / shale caprock in the top of K1yc1 form a closed cover of low abundance of gas reserves in the period were a lot later than the exhaust of gas source rocks, although the subsequent closure of capacity is gradually increased, the closure can be medium or high abundance of gas reserves of capacity, but it can be closed abundance of natural gas reserves to live only a low level based.