Pore Structure Characteristics and Their Influence on Petrophysical Properties of Carbonate Reservoirs in the Nanpu Area

Key words: 
• Nanpu area /
• carbonate reservoirs /
• pore structure /
• porosity /
• permeability

Abstract: The pore structure parameters of carbonate rocks is quantified by digital image analysis (DIA) to determine the characteristics of the pores in this complex structure and their influence on its physical properties. A model for predicting the physical properties of the carbonate reservoir is established after selecting appropriate parameters. The carbonate reservoir is a typical porous reservoir dominated by secondary pores. Application of pore-structure parameters in this way enables the various pore types in the carbonate reservoirs in the Nanpu area to be distinguished. Pore types included:moldic pores with low perimeter-over-area (PoA) and high aspect ratio; intergranular pores with low PoA and high equivalent diameter (the latter having a large standard deviation); and matrix pores, typically of high PoA and high average equivalent diameter. Of all the pore parameters, the equivalent diameter, form factor, roundness and compactness are found to have the greatest effect on porosity and permeability. Further, 28 parameters are optimized by means of correlation matrix. The best-fit relationship between pore structure parameters and porosity and permeability is established by multivariate linear regression, giving the very reasonable R² values of 0.778 for porosity and 0.916 for permeability. These results provide an ideal reference for evaluating the properties of porous carbonate reservoirs in Nanpu and in other areas.