Constraints of hydrodynamic conditions on gas reservoirs in Dongying depression and its enlightenment to CO₂ storage target area

A large number of natural gas reservoirs in Dongying depression and its surrounding areas indicate that there are good conditions for CO₂ geological storage in these areas. To optimize the target area suitable for CO₂ storage, through data collection and comprehensive analysis of Dongying basin flow field, this study summarized the main controlling factors and occurrence modes of natural gas accumulation in Dongying depression and its surrounding areas with a buried depth of 500-1500 m, and analyzed the restrictive effect of underground hydrodynamic field on the formation of natural gas reservoirs. The results show the migration pathways of shallow gas reservoirs can be divided into lateral migration pathways and vertical migration pathways based on the characteristics and modes of underground fluid movement. The lateral type is mainly distributed in the high uplift belt at the edge of the depression, and the vertical type is mainly distributed in the depression area in the basin. Compaction flow is the main driving force for the upward migration of the deep gas source in the center of the depression. A part of the deep gas moves for a long distance from the center of the depression to the edge of the depression, forming a closed hydrodynamic trap and a lateral shallow gas reservoir at the junction of compaction flow and gravity flow in the high convex part of the edge of the depression. The other part of deep gas, driven by compaction flow, migrates vertically along the high porosity and permeability fault zone and accumulates in the trap at the top. Lithologic traps caused by fault dislocation are relatively developed, which together with hydrodynamic traps form an effective trap of gas and form a vertical shallow gas reservoir. The most favorable target area for CO₂ storage in the shallow part (500-1500 m) of Dongying depression is mainly located in the west and north direction of the depression, such as Gaoqing Uplift, Linfanjia Uplift, Binxian Uplift, Chenjiazhuang Uplift, Guangrao Uplift, and their surrounding areas. The vertical fault development areas of Guangrao uplift, Qingtuozi uplift, and other depressions in the east are favorable targets for CO₂ storage in the shallows.