Gas Accumulation Regularity Of Huoshiling-Yingcheng Formation In Xiaochengzi Fault Depression,Songliao Basin

Xiaochengzi fault depression is in the northwest of the southeast uplift in Songliao Basin, with a trend of nearly east-west direction. Its mainly fault area is in the west of Xiaochengzi fault depression, and on the plane it has a fault in the west and an overlap in the east. The depression has a biggest thickness of 3928 m and an area of about 560km2.By the research of core, well log and seismic, it comes to that Huoshiling- Yingcheng formations all develop a certain size of volcanic constructions and sedimentary rock constructions. Based on the features of facies, four facies are found in Huoshiling- Yingcheng formation, namely lacustrine, fan deltaic, sublacustrine fan and volcanic facies; also 10 types of subfacies and 16 types of microfacies are found in the beds of interest. Besides, according to the reflectance signature of seismic, the results of discrimination show that the study area has 20 types of seismic facies. What’s more, this paper systematically builds a corresponding relationship between lithofacies and seismic facies.The core samples test and analysis from 28 drillings in the study area indicate that: the target of abundance of organic matter and types of kerogen from hydrocarbon source rocks in Huoshiling and Shahezi formation are better,also with a higher maturity.They come to be the source rock of nature gas.The terrigenous clastic rock of Huoshiling-Yingcheng formation all have ultra- low porosity,but different permeability:the permeability of Shahezi formation is ultra- low, the permeability of Huoshiling formation and Yingcheng formation is a little better than that of Shahezi formation,and especially Yingcheng formation has mainly low permeability. The porosity of volcaniclastic rocks of Shahezi formation is mainly type of Ⅲ,the permeability is mainly type of Ⅳ,better than that of Huoshiling formation; The porosity of volcaniclastic rocks of Huoshiling formation is also mainly type of Ⅲ,the permeability is mainly type of Ⅴ; The porosity of volcanic lava rock from Huoshiling formation is mainly type of Ⅱ~Ⅲ, the permeability is mainly type of Ⅳ~Ⅴ; There have several sets of source-reservoir-seal assemblages in target stratum. The mainly combination types of source-reservoir-seal assemblages are self source rocks and self reservoirs type, upper source rocks and lower reservoirs type, lower source rocks and upper reservoirs type and compound type.Depending on the test results of drillings and the analysis of core, seismic, structure and lithofacies, the study area are mainly gas accumulations in the Huoshiling formation and Yingcheng formation. Volcanic dome- lithological type and lithologic type are the main types of gas accumulations. Lithologic gas reservoir includes lobate sand body on the tip off type and lens type. The main controlling factors of volcanic dome- lithological gas reservoir in Huoshiling formation are: the volcanic dome structure, nearly to the high quality source rock and the inside volcanic dome with“the lava,breccia lava or tuff- lava which have qualities of accumulating”; The main controlling factors of lobate sand body on the tip off type gas reservoir in Shahezi formation are: the high quality reservoirs which is developed in the lobate sand body of fan dalta closing to the basin-controlling fault, the finger- like interaction between fan delta up-dip pinchout lobate sand body and lacustrine mudstone of contemporaneous difference facies and the high quality of source rock in Shahezi formation; The main controlling factors of lens type gas reservoir in Shahezi formation are: the reservoir space supplied by lens type sand body in middle fan of sublacustrine fan and the mudstone surrounding the sand body of sublacustrine fan having the hydrocarbon potential. What’s more, the beneficial source-reservoir-seal assemblages also do well to the development of gas accumulation in Huoshiling and Shahezi formation.Under the research above, this paper constructs a pattern of gas accumulation and points out that there are three furthersome directions of exploration in the study area: the volcanic dome structure closing to the high quality source rock in the sublacustrine fan, the finger- like interaction between the high quality mudstone in the semi-deep lake facies and the up-dip pinchout lobate sand body, the isolated lenticle of sublacustrine fan in the high quality mudstone of semi-deep lake facies.