Geological Assesement Symbols And Log Responses Of CO₂Geologic Sequestration Body In Jingbian Qiaojiawa Region

Qiaojiawa region in Jingbian oilfield is located in the middle east of Shanbei slope of Ordos Basin, the studied intervals is Chang-4+5and Chang-6members of Yanchang Formation. As the CO2storage experimental area, it has good geological and air transportation conditions. It is better to realize the geological sequestration to understand the differences between reservoirs and cap rocks comprehensively. This paper mainly study the variation characteristics of the reservoirs and cap rocks through geological evaluation and log responses.In this paper, internal rock characteristics in Qiaojiawa region are mainly research objects, in order to study all kinds of geological assessment symbols of cap rocks and reservoirs and get response characteristics on various logging curve, comprehensively analyze and study on lithological features, pore types and sizes, pore and throat features, mineral composition characteristics, clay content and change and stress pressure in studied intervals, combining with the date analysis of casting lamella, scan electron microscope, porosity measurement, grading analysis, whole rock analysis, mineral clay qualification test, high pressure Hg injection and breakthrough pressure method, and which is based on sedimentary petrography, petroleum geology and logging interpretation. We basically achieved the following results and understanding.The reservoirs are mainly composed of lithicarkoses,some lithic feldspathic sandstones, and feldspathic litharenite sandstones in studied intervals. And it is given priority to fine sand and silt, then medium sand. Reservoirs mainly experienced compaction, pressolution, cementation, dissolution and metasomatism and have significantly differences with cap rocks in physical properties including porosity and permeability. Clastic content is higher than clay mineral in reservoirs, cap rocks is just the opposite. In the cap rocks, the pore structure between particles is narrow and sizes are focused on micrometer-to nanometer, the main pore types are nter-partical pore, residual intergranular pore, intragranular dissolved pore and fissures and microfissure in reservoirs, maximum pore measurement results can reach more than50μm. Cap rocks pore are very small and do not have regular pore structure, reservoirs pore throat structure include flake, curved plate, necking throat and reduces size of the pore throat types, the capillary pressure curve can be divided into three different forms and the quality of reservoirs reduce in return. Cap rocks have a larger displacement pressure, and reservoirs differ significantly. Logging response show that gamma and shale content have a higher response value for cap rocks, reservoirs have the opposite. Combining with the results above, the cap rocks of this area are divided into good and middle, reservoirs are divided into good, middle and poor, the matching of optimal cap rocks and the reservoirs is the most favorable sequestration group that has the best sequestration capacity.