In the comparison between geochemical indices and mineral compositions in soil media over the oil-gas reservoir, the results of correlation analysis and cluster dendritic diagram analysis show remarkable differences in different areas. The correlations between geochemical indices and mineral compositions are considerably different over oil-gas reservoirs of different exploitation stages. It is found through the analysis of soil siderite over the oil-gas reservoirs that there exist differences in the average siderate contents in the margin of the oil-gas reservoir (except for the oil field of the late exploitation stage), within the oil-gas reservoir and outsite the oil-gas reservoir, and that soil siderate and heat-release hydrocarbon show different characteristics over the oil-gas reservoir and on the outskirts of the oil-gas reservoir.