Microfluidic Pore-scale Analysis of Wax and Scale Formation/Mitigation for Sub-surface Water Injections

Summary A North-Sea operator was experiencing low injectivity in a water injection well that was injecting into both the water and oil legs of the formation of interest, potentially due to wax and scale formation under operating conditions. This study was motivated by a desire to confirm wax and scaling tendency, to identify the cause of the individual scaling mechanisms, understand the individual and combined impacts on formation damage, and to evaluate the effectiveness of wax and scale prevention chemicals in mitigating the problem. This study leverages a novel microfluidic platform with integrated optical access to investigate the individual and synergistic effects of wax and scale deposition on pore-scale flow dynamics, as well as the efficacy of wax and scale inhibitors in mitigating formation damage. A microfluidic reservoir analogue, designed to replicate the porous media properties of the formation of interest, such as porosity, pore geometry, and permeability was fabricated to enable direct visualization of wax and scale deposition under representative conditions and confinement during fluid compatibility testing. A systematic investigation was conducted to examine the impact of temperature, fluid incompatibility, and the presence of chemical inhibitors on the formation and growth of wax and scale deposits. The wax appearance temperature (WAT) of the crude oil was determined to be 35.9 ± 0.1°C, and the severity of wax deposition was found to increase greatly at temperatures lower than WAT. Microfluidic study also revealed that scale deposition is more pronounced at reservoir temperature compared to near-wellbore injection temperature. Microfluidic flow tests indicated a substantial reduction in injectivity below the WAT, resulting in higher differential pressures. Remediation tests, wherein the temperature was gradually increased, demonstrated a progressive increase in oil recovery, highlighting the critical role of temperature in wax dissolution. The microfluidic tests indicated that the addition of wax inhibitors led to a remarkable improvement in both oil recovery (42%) and injectivity (45%) while scale inhibitors exhibited a more modest effect on injectivity (22%) and marginal increase in oil recovery on chip. Furthermore, the combined use of wax and scale inhibitors yielded the most significant improvement in both injectivity and oil recovery. Pore-scale visual observations revealed the formation of complex clusters composed of a mixture of wax and scale. Interestingly, the appearance of these clusters was found to be more dependent on wax presence than scale, as evidenced by the greater efficacy of wax inhibitors in reducing their formation on chip.