Pacific Section AAPG Convention

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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. Recent developments in horizontal drilling and hydraulic fracturing have changed the approach on the evaluation of potential reservoir capacity of sedimentary rocks. New techniques in horizontal drilling and fracking have made uneconomic sandstone reservoirs economic reservoirs. Therefore, to be able to evaluate and estimate reservoir capacity of these low- productive reservoirs accurately, revealing the size, shape and distribution of pores from thin sections has become a critical investigation. Within this context, we are evaluating pore size distribution (PSD) in sandstones using the methodology of crystal size distribution (CSD) theory proposed by Marsh (1988). Although this theory has been used to measure the number of crystals per unit size range per unit volume, our results show that it can easily be applied to reveal the pore size distributions in thin sections of sandstones. In this new method of measuring pore sizes in thin sections, we collected data on number of pores per unit size per unit area first, and then converted it to per unit volume using the procedure suggested by the CSD theory. This method, besides providing accurate measurements of pore sizes and areas, can also give the following additional information: 1) distribution of pores as a function of sizes, 2) percent of pores in each size range, 3) number of pores per unit area 4) number of pores per unit volume 5) number of pores per unit size interval per unit volume. This is the first attempt to use the CSD theory and image-analysis to reveal pore size distribution (PSD) in sedimentary rocks. 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 size range, and pore types and pore geometry.