Pore volume compressibilities of sandstones and carbonates from Helium porosimetry measurements

• Pore volume compressibilities measurements using Helium porosimetry.
• Differences between sandstones and carbonates regarding pore compressibilities.
• Relationship between pore compressibility and porosity.

For decades, several efforts have been put in place to understand the interaction between rock and fluids, and on the physical laws that describe the fluid behavior in a porous media. Petrophysical modeling is used in drilling, completion, compaction evaluation of the reservoir rocks and wellbore production to avoid unexpected interventions and optimize the hydrocarbon production throughout the life of the well. Pore volume compressibility is one of the main parameters to characterize the behavior of the reservoir rock as it quantifies the incremental pore volume variations due to external or internal pressures. This parameter is needed for reserve estimation, production forecasting, wellbore stability evaluation and seismic monitoring issues.In this work, uniaxial compression tests were carried out using helium gas porosimetry, which measured the variation of the pore volume for each applied load. The pore volume compressibility calculation was possible through a power-law fitting between pore volumes and confining pressure. That procedure was applied to six sandstone, six limestone and one dolomite samples at nine different confining pressures ranging from 400–2000 psi. Porosity was calculated for each pressure stage and the interdependency of the pore compressibility and porosity was evaluated, assuming that grain volume remains unaltered and using the pore volume measurements.Optical microscopy and Mercury Intrusion Porosimetry (MIP) aided to understand the pore space of some of the rocks and to quantify microporosity fraction, which impacts on a dual porosity system. This work also shows that the amount of microporosity influences how the pore volume changes as the external pressure increases. For rocks with small microporosity, the power-law behavior is likely to describe the relationship between the pore volume and the confining pressure practically perfect (R2~1), but as microporosity increases, the accuracy of this relationship decreases.