Calculating Pore Size Distribution by Using Capillary Pressure

Abstract

Abstract Pore size distribution is an important parameter in quantifying reservoir heterogeneity. A thorough understanding of different pore sizes in the rock provides a solid base for reservoir development plan and makes an accurate estimation of volumetric sweep efficiency possible. For instance, more certainty in determining pore size distribution can be valuable in accurately predicting the hydraulic flow units which in-turn affects building more reliable geological and petrophysical models for reservoirs. Conventional rock porosity estimation from core and well log only provides porosity without pore size distribution. Therefore methods used to estimate percentages of different pore size are highly desired. Our novel approach is engineered to address this issue. Starting from the capillary pressure data obtained in special core analysis, we developed a correlation in which capillary pressure is expressed as a function of pore size, water saturation, and other petrophysical parameters, which are readily obtained from well log interpretation. Through this correlation each pore size is corresponding to a unique capillary pressure and water saturation. Therefore, the calculation of percentage of each pore size can be accomplished. The pore size distribution from our method is not only vital for two and multiphase flows in reservoirs such as water drive oil and gas drive reservoirs, but also crucial in estimating the percentage of reservoir volume that can be depleted at the abandonment reservoir pressure. Thus a reliable estimated ultimate recovery can be achieved without adding much cost and time since capillary pressure and well log data that are used as inputs for calculation are readily available. Therefore, the proposed method fills the big gap in reservoir characterization and is a useful tool to supplement other methods in reserve evaluation.