Electrokinetic Driven Low-Concentration Acid Improved Oil Recovery in Abu Dhabi Tight Carbonate Reservoirs

• As acid concentration increases, displacement efficiency and permeability enhancement increase due to increased electroosmotic, electromigration and electrophoretic effects.
• At ambient conditions, 2 V/cm provides the highest displacement efficiency but lower permeability enhancement whereas at reservoir conditions, 1 V/cm provides the highest displacement efficiency and maximum permeability enhancement.
• A voltage gradient of 1 V/cm and an acid concentration of 1.2% were identified to be optimum parameters using simultaneous EK LCA-IOR approach in lab scale.
• EK Low-concentration acid IOR produces better stimulation results by 29%, better oil recovery by 15% and reduced water/acid consumption by 70%.

Conventional acidizing, though useful in increasing the effective permeability in the near well-bore region, has compatibility and operational issues such as limitation in depth of penetration and HSE issues to handle, transport and injection of high concentration acid into the well. However, the application of electrokinetics (EK) has a number of economic and environmental advantages such as reduced oil viscosity, reduced water-cut, and no depth limitation. This study presents recent research that demonstrates the impact of EK on matrix low-concentration acid stimulation in Abu Dhabi carbonate reservoirs with varying acid concentrations and voltage gradients.Core-flood tests were conducted by saturating core-plugs retrieved from Abu Dhabi oilfields with medium and light crude oil in a specially designed HPHT EK-EOR core-flood setup. Initially, EK was applied using acids of varying concentrations from 0.125 to 1.2% HCl injected at the anode to cathode (producer) at 0.25ml/min. Experiments were also repeated with low concentration HCl stimulation without the application of EK.Several correlations related to acid concentration, displacement efficiency and permeability enhancement are presented here at ambient and reservoir conditions. The experimental results have shown that the application of waterflooding on the carbonate cores yields an average oil recovery of 60%. An additional 17-29% oil recovery was enhanced by the application of EK-assisted low concentration (∼2%) HCl at Abu Dhabi reservoir conditions. In addition, EK LCA-IOR was shown to enhance the reservoir's permeability by approximately 11-53% across the tested core-plugs. Furthermore, this technique can be engineered to be a sustainable process in the presence of EK as the concentration and voltage gradient can be optimized to reduce the amount of acid injected and power consumption by 20-41%, further improving economic feasibility.