Abstract
Based on the background of sedimentary characteristics, a large amount of core and thin section analysis, taking Chang 6 reservoir of Yanchang Formation in the central and western Ordos Basin as an example, through the application of scanning electron microscopy, high-pressure mercury injection, nuclear magnetic resonance and microscopic water drive oil model, and other experimental test methods, the diagenetic facies types and microscopic pore structure characteristics of tight sandstone reservoirs are discussed and analyzed in depth. The results show that the average porosity loss rate caused by early diagenesis compaction in the study area is 50.62%, which is the main reason for reservoir compactness. The cementation further causes porosity loss, and the later dissolution increases the reservoir space in the study area to a certain extent. Different diagenetic facies reservoirs not only have obvious differences in porosity evolution characteristics but also have significant differences in pore throat radius distribution characteristics, movable fluid occurrence characteristics, and water drive oil characteristics. The pore throat distribution with radius greater than R50∼R60 determines the permeability. The difference in movable fluid saturation mainly depends on the connectivity of the relative large pore space corresponding to the relaxation time greater than the cut-off value of T2. The size of pore throat radius has a good control effect on water flooding efficiency.
Highlights
In recent years, with the decreasing of conventional oil and gas resources, the world has increased the exploration and development of unconventional energy, especially tight oil and gas [1,2,3,4,5,6,7,8,9]
Compared with conventional sandstone reservoirs, tight sandstone reservoirs are characterized by small pore throats, complex pore structure, and strong micro- and macroheterogeneity [10]
The pore microstructure, pore type, pore evolution and control factors, and reservoir performance parameters have become the focus of tight oil reservoir research [11, 12]. e Ordos Basin is an early area of tight oil and gas exploration and development in China. e tight oil and gas resources are very rich and have broad prospects for exploration and development [13,14,15]. e Ordos Basin is the second largest sedimentary basin in my country
Summary
With the decreasing of conventional oil and gas resources, the world has increased the exploration and development of unconventional energy, especially tight oil and gas [1,2,3,4,5,6,7,8,9]. E Ordos Basin is an early area of tight oil and gas exploration and development in China. E Ordos Basin is the second largest sedimentary basin in my country It is structurally located on the western edge of the North China Craton [16, 17]. E types and distribution characteristics of micropore throats restrict the quality and development effect of tight sandstone reservoirs. E complex pore throat structure characteristics lead to the changeable occurrence state and distribution characteristics of fluid in the pore throat, which directly restricts the exploration and development. Erefore, it is necessary to analyze the microscopic pore structure characteristics under different diagenesis, hoping to provide reference for the optimization of high quality target areas of tight sandstone reservoirs. Based on the auxiliary experimental results of casting thin section, scanning electron microscope, X-ray diffraction, and cathodoluminescence, the microscopic pore structure and seepage characteristics of the study area were studied by high-pressure mercury injection, nuclear magnetic resonance, and microscopic water flooding experiments. e differences of microscopic characteristics of different diagenetic phases were analyzed, and the main influencing factors of microscopic characteristics were clarified, so as to provide guidance for further understanding the heterogeneity of tight sandstone reservoirs and evaluating the effective reservoir distribution
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