Research On Deep Volcanic Reservoir Features Of Shengping Tectonic Zone In Xujiaweizi Fault Depression

Volcanic rock is the most important deep gas reservoir in Xujiaweizi faul depression. The mineralogical characteris-tics and physical property characteristics, pore type and genesis, relationship of rock facies and physical properiesof volcanic reservoir rock are systematically studied, and the result shows that the secondary pores in volcanic rocksnot only increase the effective storage space, but also play a critical role for connection of primary pore.The seeondary pores are the precondition of volcanic rocks in Songliao Basin becoming effective reservoirsThe develop-ment degree of secondary pores can be reflected by the ratio of total porosity of volcanic rock to effective porositvfrom core analysis.The closer the ratio is to 1, the better the pore is developed. Vertically, the secondary pores aredeveloped at the interface between rock facies and lithology of large volcanic rock section. The thickness rangesfrom several meters to decades of meters which is the composite resuh of leaching and coltosion.Pores and fissures are the two major types of reservoir spaces in volcanic rocks in Xujiaweizi fault-depression. The types of reservoir space in volcanic reservoirs have been found to be controlled by the facies. The volcanic reservoirs found in various facies belts have quite different pores and fissures and their assemblages.Gas cavities, fissures in rhyolitic lamination, and joint fissures have been identified mainly in eruption-overflow facies. The main pore-type identified in explosive facies is intergranular pore; and inter-breccia pore and primary fracture are dominant in extrusive facies. Joint fissures and various primary fractures are mainly developed in volcanic conduit facies. It is found that " unconsolidated formation" often distributes at the base of each cooling unit in explosiveThe volcanic rocks in Xujiaweizi fault-depression, Songliao basin, was mainly erupted in Late Jurassic toEarly Cretaceous. Their occurences are characterized by a certain geometric pattern.On the basis of the structural position of volcanic eruption and the occurrences in the basin, three types of eruption have been identified, includingeruption on the upthrown side of fault, along fracture belt and on downthrown side. Different occurrences are oftencorresponding to different basin structures. The volcanic rocks occurring along fault plane would transit gradually tosublacustrine fan -turbidite fan; the volcanic rocks occurring on the upthrown side of fault would distribute in themanner of alternating beds of volcanic rocks and sandstones; the volcanic rocks occurring on the downthrown side havemostly been covered by fine grain sediments.Ingregrating with the study of regional geologic background, the thesis has full used the geology, seismic, mud-logging, well-logging and analysis data to systematically study the formation and development characteristics of igneous rock, genesis of gas reservoir formation in Xujiaweizi Fault Depression.The result shows that Xujiaweizi Fault Depression is a half graben-like fault depression that consists of fault in the west and overlap in the east, and is controlled by the main boundering faults of Xuxi Fault and Xudong Fault which divide Xujiaweizi Fault Depression into "two uplifts and three depressions" in structural pattern.So, Fault stucture system is not only controlling depressions but also controlling source rocks, biological indicator and reservoir, as a result, it is the crucil restraining factor of influcing the accumulation of gas reservoir. Formation and distribution of igneous gas reservoir in the Rift are mainly controlled by source rock distributed area, discordogenic fault, igneous rock facies, palaeohigh and igneous caprock of its own. The models for igneous gas reservoir formation mainly include two types:Transported by the faults near source rock type and Transported by the faults far from source rock type.