Increasing depth of penetration by electrokinetic driven low-concentration acid IOR in Abu Dhabi tight carbonate reservoirs

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 of acid into the well. On the other hand, 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 paper presents recent research that demonstrates the impact of EK on matrix acid stimulation in 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 core-flood setup. Initially, EK was applied using acids of varying concentrations up to 1.2% HC1 injected at the anode to cathode (producer) at 0.25ml/min. Experiments were also repeated with low concentration HC1 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 on aged oil-wet core-plugs. 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 HC1-IOR (EK LA-IOR). In addition, EK LA-IOR was shown to enhance the reservoir's permeability by 32% on average across the tested core-plugs. It was observed that low acid concentration with application of low voltage EK, recorded a maximum oil displacement of 81% at reservoir conditions. 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.