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Deep basin gas, which is trapped deep in a basin, is a kind of unconventional natural gas. It is also one of the important unconventional gas resources. In the previous studies of the mechanism of deep basin gas accumulation, force balance and material balance are considered as essential conditions for the formation of deep basin gas reservoirs. However, the gravity of natural gas is not fully taken into account in the analysis of force balance. In this dissertation, the density of natural gas under the condition of underground temperature and pressure is calculated by using the EOS. The result shows that the density of natural gas cannot be neglected and the PR EOS is applicable to the analysis of the relationship between the volume of natural gas and the condition of underground temperature and pressure.

The subtle reservoir has become an important exploration target within the Bohai Bay Basin, especially in the Qikou sag. In order to guide subtle reservoirs exploration in offshore area geological analysis to Sha’nan structural belt is carried out in this paper. Qikou sag has large thickness, high abundance, ideal type hydrocarbon source rock. By unconformity recognition technique and paleotectonic analysis technique, results show that tectonic uplift had provided sedimentary source to the depression around it after Es1. By 3-D seismic interpretation technique and Seismic facies analysis, the sedimentary facies was confirmed. Geological analysis results show that sand bar, subaqueous fan is developed around it in Ed3. With the new geological analysis data sedimentary model of Sha’nan structural belt has been built in this paper. The sand bar and subaqueous fans showed a good reservoir potential, which are advantageous to oil accumulations. The southern part of Sha’nan structural belt has good hydrocarbon exploration potential.