A NEW METHOD OF DETERMINING PORE SIZE DISTRIBUTION IN SEDIMENTARY ROCKS

Determination of porosity in sedimentary rocks is central to the evaluation of potential storage volume for hydrocarbons. Pore size distributions (PSD) of reservoir rocks are one of the most important parameters that affect the fluid flow in oil/gas reservoir rocks. Within this context, we are examining PSDs of sandstones using a new method combining Digital Image Analysis (DIA) with an empirical equation that was suggested by Marsh (1988) to determine crystal size distribution of rocks. This is the first attempt to use the CSD theory along with image-analysis to determine (PSD) in sedimentary rocks. In this new method of measuring pore sizes in thin sections, we collected data on the number of pores per unit area in each class interval first (2D), and then converted it to the number of pores per unit volume for each class interval (3D) using the procedure suggested by the Crystal Size Distribution (CSD) theory. This method, in addition to providing accurate measurements of pore sizes, also gives the following additional information: 1) distribution of pores as a function of sizes, 2) percent of pores in each class interval, 3) the number of pores per unit area in each class interval 4) the number of pores per unit volume 5) the shape of the pores. The results of the study show that pore sizes in a thin section decrease with increasing depth (compaction effect). Besides providing new information about pore size distribution, this approach can be extended to evaluate distribution of pore sizes as a function of depth in a drill core, percent of pores in each class interval, and pore types and pore geometry.