Fig. 2. The conceptual model of lower limit of buoyancy reservoir formation and its control effect on the formation and distribution of conventional and unconventional oil and gas reservoirs[25, 34]. (a) In the process of burial, the buoyancy of oil and gas in the target layer is basically unchanged, but the capillary force is increasing, which leads to the change of oil and gas migration power from buoyancy dominated to non-buoyancy dominated; (b) Geological characteristics of reservoir formation and distribution under different burial depths and their correlation with the lower limit of buoyancy accumulation; (c) The maximum pore throat radius of the target layer decreases with the increase of burial depth, resulting in the migration and accumulation of oil and gas in shallow reservoirs with large pore throat radius being dominated by buoyancy, while in reservoirs with large pore throat radius, the migration and accumulation are dominated by non-buoyancy. The lower limit of buoyancy accumulation of sandstone reservoir usually corresponds to porosity of 10% ± 2%, permeability of 1×10-3 μm2 and throat radius of 1 μm.
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