Impact of Low Concentration Ferric Chloride on Physical and Electrical Parameters in Low Permeable Limestone Formation

Variation in rock type or any physical alterations in the rock has great impact on the Archie's parameter, unlike the brine conductivity which has no influence on these parameters. When the Ferric chloride (FeCl₃) solution is injected into limestone formation, it reacts with the carbonates and alters the permeability. The current study aims to investigate the impact of low concentration FeCl₃ on physical and electrical properties by intentionally altering the rock's characteristics which in turns changes the resistivity. The study uses Indiana limestone core samples having length of 2 inches and diameter of 1.5 inches. The centrifugation method was used to achieve uniform FeCl₃ saturation levels inside the core samples while investigating the variation in their physical and electrical properties. The resistivity of core samples were determined at different FeCl₃ saturations to examine its effect on the electrical properties. Medical CT was conducted on the core sample, both before and after treatment in order to understand the structure variation during the saturation and De-saturation. Furthermore, NMR analysis was performed for comprehensive insight into the pore system and fluid distribution inside the core sample. Additionally, geomechanical analysis showed a moderate decrease in Young's modulus and a slight increase in Poisson's ratio, consistent with mild matrix weakening. The initial porosity and permeability of samples were measured to be 17.7% and 16 mD respectively. The results indicates that the Archie equation can be modified for fluid-rock interaction, providing a better understanding of the resistivity changes in the limestone formation. The findings also showed the stimulation of the limestone reservoir due to the acidizing effect of FeCl₃. The FeCl₃ on interacting with water forms HCl which is responsible for dissolving the carbonates present in the limestone samples developing wormhole across the core sample, enabling the enhanced fluid flow through the rock. The stimulation of rock can be quantified by resistivity changes and enabling precise estimation of Archie parameters. This stimulation also causes a variation in the porosity and permeability of the core samples. The NMR results suggests that the contribution of macro pores in total porosity has shifted towards the micro pores. This research highlights the impact of FeCl₃ interactions when applying Archie's Law in reservoir engineering. FeCl₃ in low concentration can be used as acidizing agent in limestone formation and enhancing its permeability for improved hydrocarbon recovery. The experimental results provide a pathway for refining Archie parameters in limestone formations undergoing stimulation and the individual pore contribution to the porosity shifts from a large pore system to small pore system.