Understanding the Dynamics of Matrix-Fracture Interaction for Suitable Fracturing Fluid Design and Chemical EOR in Unconventional Oil/Gas Recovery

Abstract

Abstract The effects of chemical additives on mitigating water-blocking and improving oil recovery were experimentally examined for gas-water and oil-water systems in spontaneous imbibition cells. In these attempts, two factors are critically important: (1) Understanding the physics of the interaction, whether it is co- or counter-current, and (2) characteristics of the chemical additives to suitably orient the interaction for specific purposes (accelerate/decelerate matrix-fracture interactions). Co- and counter-current imbibition experiments were conducted on sandstone rock samples using various oil samples (viscosities between 1.37 and 54.61 cP) as well as gas (air). The selected new-generation chemical additives include deep eutectic solvents, cationic/anionic/nonionic surfactants, inorganic and organic alkalis. We observed that the functionality of the chemicals varied depending on the fluid type, interaction type (co- or counter-current), and application purposes. For instance, chemicals such as cationic surfactant CTAB significantly reduced water invasion into the gas-saturated sandstone cores during fracturing, while chemicals such as a nonionic surfactant (Tween 80) provided considerable oil recovery improvement in the oil-saturated sandstone cores. The surface tension and wettability of the rock surface are crucial factors in determining the suitability of chemicals in mitigating water blockage. In terms of the oil recovery, certain chemical additives, such as O342 and Tween 80, may result in a lower recovery rate in the early stage because their strong ability in IFT reduction but could lead to a higher ultimate recover factor by altering the wettability. Additionally, the introduction of chemicals resulted in notable spontaneous emulsification, especially in counter-current imbibition, thereby enhancing oil recovery. The spontaneous emulsification and its stability are influenced by factors such as oil drop size, boundary condition, interaction type, IFT, wettability, as well as rock surface charges. The results have implications for understanding the physics and dynamics of matrix-fracture interactions in co and counter-current conditions. Additionally, they offer practical insights for selecting appropriate chemical additives in hydraulic fracturing fluid design and enhancing oil recovery in unconventional reservoirs.