A Type Curve for Carbonates Rock Typing

Rock typing for heterogeneous carbonates is still a standing problem. The present work was directed to investigating the relationship between microscopic geological characteristics of carbonates and architecture of the pore systems in the effort to develop a better method for carbonates rock typing. Eight carbonate reservoirs with complete core analysis data of 1,838 core plugs were used in this work. Six carbonate data sets were utilized in developing the method and the rest two were used for verification. The well known Kozeny’s equation was employed to provide the relationship between pore geometry and the structure. It can be shown that these pore attributes contain only permeability and porosity. A comprehensive analysis was then carried out by plotting pore geometry against pore structure on log-log graphs (PGS cross-plot) and identifying microscopic geological features of every core plug employed. Results for each carbonate data set show that the data points divides into six to thirteen clusters, each cluster has its own similarity in the microscopic geological features, the fitting line drawn on each cluster has very high correlation coefficient, the space between two closest fitting lines is all practically the same, and interestingly all the fitting lines tend to converge to a single point. A mathematical analysis done confirms the existence of this point, leading to the construction of a type curve. The rest two carbonate data sets perfectly verify this type curve. This work differs from the previous ones in that the present work honors both geological and engineering aspects equally and reveals that certain diagenetic processes have produced certain pore architecture as exhibited on the PGS plot. This paper overall provides a better understanding about rock type definition, a tool to identify the effects of diagenetic processes on rock properties, and a type curve for easy rock typing.