Pore throat structure analysis and permeability prediction method of tight sandstone: a case study of Jurassic Shaximiao Formation in central Sichuan Basin

Abstract

Subtle characterization of pore throat structure and permeability prediction of tight sandstone reservoir are the key for quality reservoir evaluation and development. Taking Jurassic Shaximiao Formation in central Sichuan Basin as an example, the pore throat structure is statically characterized by HPMI and fractal theory. The relations among pore throat structure, fractal dimension and reservoir physical property are discussed, the contribution of pore throat structure to permeability is analyzed, and a permeability prediction model is established. The samples of Shaximiao Formation can be divided into four types: type Ⅰ samples have low displacement pressure, favorable physical properties and good pore connectivity; the average fractal dimension is 2.11, the pores are mainly macropores and mesopores with radius >0.1 μm, and the pore throat with radius >1 μm contributes more than 90% of the permeability. As for type Ⅱ samples, the displacement pressure are 0.4-1.0 MPa, the average porosity and permeability are 9.72% and 0.375×10-3 μm2, respectively, and the fractal dimension is 2.20; the mesopore content increases and mesopores contribute most of the permeability. The displacement pressure and fractal dimension of type Ⅲ and Ⅳ samples are significantly higher than those of type Ⅰ and Ⅱ samples, and the low porosity and lack of macropore lead to low permeability. The macropores and mesopores with radius > 0.1 μm contribute more than 98% of the permeability of Shaximiao Formation. Fractal dimension is a good indicator of pore throat structure. Fractal dimension is significantly negatively correlated with pore throat radius, maximum mercury saturation and permeability, and is positively correlated with displacement pressure and relative separation coefficient of pore throat. There is a strong correlation between fractal dimension and pore throat composition, and a permeability quantitative prediction model based on fractal dimension, porosity and maximum pore throat radius is established.

Keywords

• fractal dimension
• pore throat structure
• permeability
• tight sandstone
• shaximiao formation
• jurassic
• central sichuan basin