EXPERIMENTAL ANALYSIS OF RESERVOIR AND SEEPAGE CHARACTERISTICS OF TIGHT OIL SANDSTONES IN FUXIAN AREA SOUTHEASTERN ORDOS BASIN CHINA

The research on the storage and seepage properties of continental tight oil sandstone reservoirs is of great significance for formulating reasonable reservoir development plans. In this paper, taking the Chang 8 Member of the Yanchang Formation in the Fuxian area of the southeastern Ordos Basin as an example, the key elements in the evaluation of tight oil reservoir sweet spots, such as petrology, sedimentary facies, microscopic pore structures, physical properties and seepage characteristics of tight oil reservoirs were systematically investigated. The results show that the lithology of Chang 8 Member in the study area is mainly feldspar sandstone, followed by lithic feldspar sandstone. The Chang 8 Member is a delta front subfacies deposit, and its pore types include intergranular pores. intragranular pores. interstitial pores and micro-fractures. The Chang 8 reservoir has an average porosity of 8.48% and an average permeability of 0.207 mD which is a low-porosity and ultra-low permeability reservoir. With the increase of porosity, the permeability has an increasing trend, but the trend shows irregularity. This shows that the permeability is affected by the microscopic pore structures in addition to the porosity. The factors affecting the physical properties of Chang 8 reservoir in this area include sedimentation, burial compaction, cementation and dissolution. The underwater distributary channel sand bodies of the delta front are good oil and gas reservoirs. There is a negative correlation between the content of detrital mica and porosity. The carbonate cement content in the Chang 8 reservoir in the study area is 1%-30%, with an average of 6.5%. The carbonate content is negatively correlated with the reservoir physical properties, the higher the carbonate content, the worse the reservoir physical properties. The secondary pores formed by dissolution account for 10%-40% of the total surface porosity, with an average of about 24%. Due to the high irreducible water saturation in the oil-water relative permeability curve of the Chang 8 reservoir group, the water saturation at the isotonic point is about 46%, with an average of 46.81%. In addition, the irreducible water saturation of Chang 8 water flooding experiment was 27.19 A, the final oil displacement efficiency was 47.55%, and the water flooding recovery rate was high. This study can provide basic data for the formulation of efficient tight oil development plans.