RESERVOIR CHARACTERISTICS AND MAIN CONTROLLING FACTORS OF CHANG 7 MEMBER IN NORTHERN SHAANXI SLOPE, ORDOS BASIN

The Chang 7 member in northern Shaanxi slope, Ordos Basin is a typical low-porosity, ultra-low-permeability tight oil reservoir, and it is a potential oil development zone. Reservoirs are an important factor controlling the enrichment and distribution of oil and gas, and the study of reservoir characteristics is an important part of oil and gas exploration. Based on core, logging and drilling data, this study investigates the reservoir characteristics and main controlling factors, such as sedimentary microfacies, quartz content and diagenesis, of the Chang 7 member by using different test methods. Among them, cast flakes are prepared, and scanning electron microscopy and X-ray diffraction are adopted in laboratory. The experimental results reveal that the rock types of the Chang 7 member are dominated by feldspar lithic sandstone with a porosity range of 6.33-9.3% and an average of 7.15%. The permeability range is 0.001 similar to 0.506mD with an average of 0.24mD, indicative of a low-porosity and ultra-low-permeability reservoir. Analysis of the main controlling factors indicates that sedimentary microfacies, quartz content and diagenesis have had the greatest impacts on reservoir development. The sedimentary facies mainly control the range and scale of the reservoirs distribution, while the quartz content and diagenesis determine its physical properties. Comprehensive evaluation of the reservoir in the study area shows that the Chang 7 area is dominated by type I and II reservoirs, accounting for about half of the total area of the district.