The role of salt dissolution on the evolution of petrophysical properties in saline-lacustrine carbonate reservoirs: Pore structure, porosity–permeability, and mechanics

Abstract

The invasion of low-salinity fluids into saline-lacustrine reservoirs may induce salt dissolution, resulting in significant changes in petrophysical properties. Accurate characterization of these changes due to salt dissolution is critical for efficient drilling and development. Here, low-salinity core flooding experiments and several core analysis technologies were employed to investigate the changes in pore structure, porosity–permeability evolution, and mechanical properties. Ion compositions in outlet fluids analyzed in real-time to determine the dissolved salt mineral compositions, mainly include halite (1.66 %), anhydrite (7.32 %), and glauberite (0.98 %). Salt dissolution produces many dissolution pores, especially with sizes ranging from 0.01 to 10 μm, broadens the seepage channels, and enhances the connectivity between pores, which significantly improves rock porosity close to 1.80 times the initial one and permeability to 70 times initial one. During the salt dissolution process, the stability of clay minerals is weakened to induce dispersion, migration, and swelling behavior, leading to the reduction of porosity and permeability. A semi-empirical power law relating expressing porosity and permeability for saline-lacustrine reservoirs is proposed, allowing for salt dissolution and clay swelling during the invasion process of low-salinity fluids. Although salt dissolution could slightly relieve stress sensitivity damage by 56.54 %, it significantly weakens rock strength by reduction of elastic modulus (43.51 %) and compressive strength (61.54 %). The positive and negative effects of salt dissolution on petrophysical properties are critical to guide the development of formation damage control measures for saline-lacustrine reservoirs.