Research On The Restoration Of Paleogeomorphology And Its Impact On Gas Reservoir Distribution

Block 41-33 of Sudong is located in the northeast of the Yishan slope in the Ordos Basin.The long-term sedimentary intermittent weathering crust unconformity forms complex karst-paleogeomorphology.It is an important exploration area for ordovician carbonate gas reservoirs in Sulige gas field.Based on the latest drilling,logging,seismic and production performance data,this article takes the weathered crust reservoir of the member 5 of Majiagou formation as the research object,and uses the geophysical method,residual thickness method and impression method to accurately describe the ancient landforms.Through the core observation,thin section identification,mercury intrusion experiment and other analytical methods to complete the study of reservoir geological characteristics,gas reservoir development characteristics and gas-bearing systems,systematically summarize the distribution characteristics of gas reservoirs and main control factors,and further clarify the impact of paleomorphology on the distribution of gas reservoirs.It provides strong support for the Ordovician gas reservoir enrichment area in this area.Mainly achieved the following research results:1.The thickness of the upper and lower strata of the Ordovician paleo-weathering crust is divided into five types: upper thinner and lower thinner,upper thinner and lower thicker,and upper thicker and lower thinner.Based on the sedimentary thickness and residual thickness,a quantitative index for the division of the three-level karst unit in the work area is established: South Central Development of contiguous mounds with a restoration thickness of less than 15 m and a residual thickness of more than 85m;two eroded trench belts in the north with a filling thickness greater than 20 m and a residual thickness of less than 45m;the ancient slopes are divided by ancient mounds and trenches,and the residual thickness Between 45?85m,the restoration thickness is greater than 10 m.2.The member 5 of Majiagou formation in the Z94 well area is the most complete preserved.The reservoir lithology includes micrite dolomite,fine-powder dolomite,etc.,with dissolved pores and intercrystalline dissolved pores as the main reservoir storage space.Fractures,the reservoir has strong heterogeneity,and the physical properties of the reservoirs are best developed in Ma41 a and Ma13 Member,which is generally characterized by the coexistence of low porosity and low permeability matrix and local high permeability fracture-cavity system.3.The gas layers in Ma1-2 and Ma41 a Member are the best developed.The study area is divided into two gas-bearing systems by dividing the two sets of caprocks of Benxi Formation and Ma3 Member.The Benxi Formation is a lithologic caprock,and Ma1-2 Member are the first gas-bearing layer system of the reservoir and Ma3 Member is the physical cap layer,and Ma4 Member and below are the second gas-bearing layer system of the reservoir.4.The paleomorphology determines whether the main producing layers of the gas reservoir are intact,and it is the main controlling factor for the distribution of the lower paleogas reservoirs: the main gas layers in the ancient residual hills and the edge of the residual hills are well preserved and well connected,and the horizontal subsurface flow zone and the vertical seepage zone Both are well-developed and easy to form high-dissolution pores and become favorable reservoir development areas;low-relief ancient trenches are the gathering place for dissolved substances,and the degree of pore filling is high,which leads to relatively poor storage performance of karst zones,and suffers from erosion and cutting Layer preservation is poor.5.Comprehensive analysis of the controlling factors of gas reservoir distribution,it is believed that there is no shortage of gas supply in the study area,and that high-quality reservoirs and sealing caps are developed.The distribution of gas reservoirs is affected by three major factors: paleomorphology,local structure and reservoir heterogeneity Control;relatively speaking,in areas with relatively high structural parts and relatively gentle areas,the distribution of gas reservoirs is mainly controlled by paleo-geomorphology and reservoir heterogeneity,low-structural small-scale structural development zones,and gas reservoir distribution is controlled by paleo-geomorphology and local structures More obvious.