Research on the relationship between hydrocarbon source-reservoir assemblage system and lacustrine level changes in Triassic period of Lunnan area

Abstract

The lacustrine level changes affects the sedimentary process of the basin, and has an important influence on the hydrocarbon source-Reservoir assemblage system. In this study, the method of wavelet transform and Fisher plot were used to identify 58 high-frequency cycles on drilling well, with an average cycle thickness of 8.21 m. On this basis, the cumulative offset value was calculated, and finally the lacustrine level changes curve was established during the Triassic period in Lunnan area. The results show that there were three obvious lacustrine level fluctuation cycles in the Triassic period in this area. In the descending stage of lacustrine level, the grain size of the sediments in the study area is large, mainly medium-fine sandstone. In the ascending stage of Lacustrine level, the sediment granularity is small, mainly fine-siltstone and mudstone deposits. Under the control of lacustrine level changes, three sets of “binary structure” lithologic assemblage were deposited in the study area, with large grain size lower and small grain size upper. It is found that the sandstone in the lower part of the “binary structure” has good porosity and permeability. The average porosity of the TⅢ oil formation of Karamay Formation is 15.80 %, and the maximum permeability is 3.785 μm2, which can be used as a good reservoir. The TOC content of the upper part of the “binary structure” is very high, and the average TOC is 3.8 % in Huangshanjie Formation, which is a very good source rock. Therefore, lacustrine level changes in this area has a very important control effect on the on the hydrocarbon source rock and reservoir.