Micro-Pore Characteristics and Recoverability of Tight Oil Reservoirs

Tight oil reservoirs mainly include tight limestone and tight sandstone, and there are significant differences in their microscopic characteristics. However, there are relatively fewer comparative studies on tight limestone and tight sandstone, so it is very important to study micro-pore characteristics and recoverability of different lithology tight oil reservoirs. By combining cryogenic nitrogen adsorption surface area, nuclear magnetic resonance and high pressure mercury technology, this paper comprehensively described the pore structure differences between tight limestone and tight sandstone from various scales including nano scale, submicron scale and micro scale, analyzed the effect of pores at different scales on permeability and fluid occurrence state, and studied the difference of the starting pressure gradient and the effect of throat on the starting pressure gradient. Taking the central Sichuan limestone and Changqing sandstone as an example, the results show that the tight oil reservoirs have development potential with permeability of more than 0.01 mD, in tight limestone, the submicron and micron scale pores are important reservoir and flow spaces, and in tight sandstone the micron scale pores are important reservoir and flow spaces, which are key to effective development. Based on numerous microscopic experimental analysis and low permeability reservoir evaluation methods, 8 grading evaluation parameters of tight reservoir were proposed and grading evaluation boundaries were determined, which is of great significance to determine the target of tight reservoirs and select the preferred blocks to build capacity.