The Study On Volcanic Rocks And Their Natural Gas Accumulation Of Xujiaweizi Fault Depression, In Songliao Basin

Xujiaweizi fault depression is the biggest fault depression in the deep Songliao basin, and there ia a lot of natural gas in the Mesozoic igneous rock traps. The paper mainly took igneous petrology, reservoir geology, basin analysis and petroleum geology as a guidance, took igneous reservoir appraisal and prediction, and natural gas pool forming as its backbone and used core samples data, seismic data, logging data and testing data. The paper utilyzed chemical testing and identification of rocks, ESR method, fluid inclusion identification, igeous rock reservoir prediction and other methods to discuss the forming and evolution of the fault depression, igneous lithofacies, reservoir characteristics, the forming and prediction of traps on the basis of the identification of cycles of vocanic activity and volcanic rocks, which is the part of the paper, and finally discussed the the forming and distribution rules of the natural gas pools. The main achievements of this paper made as follows: 1. Two volcanic sequences were recongnized in Sonliao basin in Mesozoic, one is Huoshiling sequence (J3h), another is Yincheng sequence (K1yc). Songliao basin was formed under the environment of inner rift in the active continental margin with pacific plate subduction. 2. The accurate name of the volcaic rocks from the basin obtained according to the IUGS recommendation principles. The acidity, series, assemblage of the volcanic rocks in the basin were determined through the study of geology, petrology, and geochemistry in detailed. The succession, volcanic apparatus, volcanic structure and porosity of the volcanic rocks in the basin were classified in detailed. 3. According to the chemical characteristics of rocks, mineral components, texture and structure characteritcs, volcanic rocks in the research area were classified into two classes (lava and volcanoclastic rock) and several subclasses. The standards of logging parameters which used to identify the lithology of volcanic rocks was established according the radioactivity chacteristics of each kind of volcaic rocks, then built a appraisal methods using logging parameters and finnaly quantitatively evaluated the qualities of igeous rock reservoir. 4. It was the first time to use lithofacies, weathering degree, compensating seismic attributes parameters and well-constrained seismic inversion to comprehensively predict igneos reservoir. 5. Based on the analysis of genetic type of natural gas and the genesis of nonhydrocarbon gas, it was indicated that natural gas in the research area is mainly coaliferous gas, secondly composite type and little petroliferous gas. The content of nonhydrocarbon gas is small, which are mainly carbon dioxide and nitrogen. 6. The paper analyzed the forming geological conditions of natural gas pools in the research area. Based on the division of petroleum system and establishment of natural gas pool forming model, the paper analyzed the controlling factors of the forming of the natural gas pools and choosed four ignous lithologic traps.