Effect of pore type on porosity, permeability and pore volume compressibility of geological formations due to in-situ stress change

Abstract

Understanding the behavior of reservoir rocks under various in-situ stress conditions is important for compaction evaluation, reserve estimation, production forecasting, pressure maintenance, and casing collapse diagnosis. Such a behavior can be affected by change in rock porosity, permeability and pore volume compressibility which are all functions of rock pore type under various stress magnitudes. Thus, in this study the significance of pore type in determination of porosity, permeability and pore volume compressibility under different hydrostatic stresses were investigated. Twelve carbonate samples with four different pore types including touch vug, non-touch vug, porous matrix and tight matrix were tested hydrostatically. Samples with touch vug and tight matrix pores revealed the minimum and maximum porosity and permeability effects under various effective pressures, respectively. Also, samples with touch vug pore demonstrated a sharp reduction in their pore volume compressibility at the initial steps of measurement while the pore volume compressibility of samples with non-touch vug pore resulted in a fluctuated trend and less reduction compared to the samples with touch vug pore. Finally, it was noted that the samples with tight matrix pore type are deemed to have the lowest pore volume compressibility.