Generation and filtration of O/W emulsions under near-wellbore flow conditions during produced water re-injection

Produced water in the oilfield contains oil droplets in the form of oil-in-water (O/W) emulsions. These oil droplets cannot be completely separated from the water by surface facilities, and produced water still containing suspended emulsions is re-injected into formations. These oil droplets plug the pore space in the near-wellbore or near-fracture region, resulting in rapid declines in the performance of water injection wells where the remediation processes can be expensive. Displaced oil droplets also contribute to the plugging of pore space near injection wells. These oil droplets are generated by high-velocity flow displacing residual oil in the rock. Because generation and filtration processes occur simultaneously, it is critical to understand both processes at high-velocity flow conditions. This paper experimentally quantifies the rate of generation and filtration of oil droplets in high-velocity flow. For the first time, empirical models were suggested to predict droplet size and rate of generation as a function of trapping number. For the filtration, synthetic dilute O/W emulsions were injected into granular packs to measure the filtration coefficient at various trapping numbers, grain sizes, and fluid velocities. We compared the measurements with known models. Also, filtration mechanisms of straining and interception are explained under high-velocity flow conditions experienced near injection wells. Based on this work, a macroscopic material balance model of O/W emulsion flow in porous media can precisely predict the near-well formation damage and the subsequent performance of injection wells during produced water re-injection (PWRI).