Experimental Study on Porosity & Permeability Characteristics of Typical Tight Oil Reservoirs

Abstract

Tight oil has become one of the important energy sources for increasing reserves and production in China’s oil and gas field. Chang 8 Member of Ordos Basin shows great exploration potential, and the classification and evaluation of tight reservoirs are critical to reservoir optimization and reserve evaluation. However, the classification and evaluation of tight reservoirs in Chang 8 Member of Ordos Basin have not been unified. Therefore, on the basis of previous research results, this paper systematically studied the petrological characteristics, physical properties and microscopic pore throat structure characteristics of tight sandstone reservoirs by means of rock slice observation, overburden porosity and permeability test and high-pressure mercury injection test. On this basis, the weight coefficient of the correlation between the key parameters and the oil-bearing property of the reservoir is determined by screening the key parameters, and the mathematical model of reservoir classification evaluation is established by using the analytic hierarchy process. The research results show that the reservoir composition maturity of Chang 8 Member in Ordos basin is medium, and the lithology is mainly lithic arkose and feldspathic lithic sandstone. The physical property of Chang 8 reservoir is poor, and it belongs to low porosity, low permeability ultra-low permeability reservoir as a whole. The reservoir space is dominated by intergranular pores and dissolution pores, and micro fractures are developed locally. The pore throat structure of the reservoir is fine, and the pore type is smaller than 10 μm, and the throat and micro throat are dominant with 0.2 μm. Considering porosity, permeability, displacement pressure, average pore throat radius and other parameters comprehensively, normalize each parameter, and determine the weight of each parameter according to its correlation with oil saturation. The reservoir classification and evaluation model were established by using the analytic hierarchy process (AHP), and the reservoir quality index (RMI) is used to classify the reservoirs of Chang 8 Member in Ordos Basin into 4 types. This study can provide a basis for efficient exploration and development of tight oil.