Characteristics And Distribution Of GAS Reservoirs Of Carboniferous-permian In The South Of Jinxi Flexural Structural Belt

This paper focused on the research of the gas reservoir characteristic and distribution in the south of Jinxi Flexural Belt. On the basis of the study of the formation and preservation of natural gas reservoirs in Carboniferous - Permian coal bearing strata, the sandstone gas reservoirs are identified and evaluated, and the distribution characteristic of gas bearing sandstone are studied. Then the paper analyzed the main controlling factors of sandstone gas reservoir, and established the gas reservoir section. The paper summarized the types and distribution of gas reservoir, and predicted the resource potential of the study area, and elected the favorable area.The study area has a good gas reservoir forming condition of gas generation,storage and preservation. Coal, dark mudstone and other hydrocarbon source rock in Carboniferous - Permian formation have high abundance of organic matter, stable thickness and wide distribution. The organic matter of source rock is in the stage of mature and over mature thermal evolution, with strong hydrocarbon generation capacity. The sand body is widely distributed in the plane, and the thickness of the stack is large. Based on the analysis of four sets of main sand bodies in the study area,it shows that the reservoir is mainly tight sandstone. The caprock condition of the study area is better, and the thickness of mudstone caprock is stable, and the displacement pressure is high. In the preservation condition, the whole structure of the study area is the westward dipping of the monoclinic, local development of small folds, and the fault is not very developed; Magmatic activity is not obvious; The salinity of groundwater is higher, indicating that the run-off condition is weaker ,which is favorable for the storage of gas reservoir.The sandstone gas reservoirs in the study area were identified and evaluated.First of all, the paper first use the method of curve overlap and intersection chart to identify the sandstone gas reservoir in this area, and established the method of identification and evaluation for gas reservoir. In consideration of the sandstone high mud content, the paper optimized the parameters of Indonesia formula. The sandstone gas content was calculated, and gas content as a whole appeared a "South high north low, west high east low" rule.The main controlling factors of gas reservoir are analyzed, and the types and distribution of gas reservoir are summarized. By using linear regression, partial correlation analysis and grey correlation coefficient, the main controlling factors of sandstone gas content in the study area are as follows: sandstone porosity, caprock displacement pressure and gas saturation. There are three types of gas reservoirs in this area: structural gas reservoir, lithologic gas reservoir and structural - lithologic composite gas reservoir, and lithologic gas reservoir and structural - lithologic composite gas reservoir are the main reservoir. It is concluded that the distribution law of gas reservoir in this area is as follows: 1. The distribution of gas reservoir controlled by the assembling of reservoir and cap; 2. The distribution of lithologic gas reservoirs controlled by sandstone physical properties; 3. The natural gas accumulated in the high position of the structure and the regional slope.Finally, according to the area abundance method, the resources of sandstone natural gas in the south of Jinxi Flexural Belt is predicted, totaling 9872.16×108 m3.According to the main controlling factors of sandstone gas reservoir, the favorable area of this area is selected, that is, the surrounding area of Y148 - well Y155, the surrounding area of Yi 10 - well Yi 18 and the surrounding area of Daji6-5 - well Jishi 20.