Pore compressibility of reservoir sandstones from integrated laboratory experiments

Abstract

Understanding the pore structure and the compressibility changes with formation pressure is crucial for determining reservoir properties. Knowledge of these parameters is essential in optimization of hydrocarbon production. Fluid removal from a reservoir increases the effective stress causing reduction of porosity and permeability, and changes pore compressibility. While pore compressibility, and pore compressibility and porosity relationship have been studied extensively, there is a lack of research done on pore compressibility from Nuclear Magnetic Resonance (NMR) relaxation. The method consists of determining the pore compressibility by looking at the change in porosity values as a function of confining pressure. This method of pore compressibility determination will provide us with static measurement, which is closer to rock properties at reservoir conditions. Using the NMR tool, we can determine the pore compressibility of individual pore structures in the reservoir. In this study, I investigate pore size distributions and pore compressibilities for Hibernia and Berea sandstone samples. The Hibernia samples exhibit homogeneous mineralogy and wide range of porosities and permeabilities. I present pore compressibility values, determined from NMR and spectral induced polarization (SIP) pore size distribution, as well as pore compressibilities, calculated from helium porosimetry (CMS-300), and ultrasonic velocity measurements. SIP and CMS-300 data were used to validate the NMR pore compressibility calculation. The pore compressibility from these three measurements are in good agreement. The compressibilities calculated from NMR, SIP and CMS-300 are static data. Ultrasonic velocity measurements were conducted to determine the dynamic pore compressibility. A correlation between static and dynamic pore compressibility was established. Static measurement exhibits higher pore compressibility compared to the dynamic data. This correlation is usable to convert the dynamic acquired data into static data, especially for this formation. This acquired correlation can be used in geomechanical modeling of the reservoir behavior.