A Novel Cost-Effective Approach for Enhancing Capillary Number while Stimulating Abu Dhabi Tight Carbonate Reservoirs

Abstract

Abstract Electrokinetic Low-concentration acidizing is one of the emerging technologies where the application of the Low-concentration acidizing is integrated with electrokinetic enhanced oil recovery (EK-EOR) as presented in previous studies [Ansari et al., 2014-2015]. This research focusses on analyzing the effectiveness of the EK LCA-IOR process in Abu Dhabi tight carbonate reservoirs by qualitatively analyzing the improvement in the capillary number and increase in depth of penetration. Core-flood tests were conducted by saturating Abu Dhabi carbonate core-plugs with medium crude oil in a specially designed core-flood setup at reservoir conditions. After the waterflooding stage, EK LCA-IOR was applied under optimum conditions (1.2% HCl concentration, 1V/cm voltage gradient), where acid was injected and transported by EK to the target producer. Moreover, the capillary number change, Single Energy CT Scan (SECTS) and oil API gravity change results were analyzed in order to observe the effect on rock-fluid interaction to control rock adsorption capacity through interfacial tension and depth of penetration. Several correlations at reservoir conditions related to acid concentration, displacement efficiency and permeability enhancement have shown that the application of waterflooding on the carbonate cores yields an additional 15-28% oil recovery beyond the waterflooding limit (58%), recording a maximum oil displacement efficiency of 88% and maximum permeability enhancement of 53%.EK LCA-IOR also improves the capillary number by 500% in Water-wet core plugs and 1500% in Oil-wet core plugs, mainly due to a decrease in interfacial tension, increase in crude oil API gravity by 20-40% with an increase in API gravity of about 10-18%. The use of SECT imaging confirmed wormhole orientation and propagation length across core-plugs, precisely delivering the acid front throughout the core-plug and also indicate the decrease in acid adsorption as acid is precisely transported to the targeted production well through the tortuous path. EK LCA-IOR may offer a feasible option to augment the efficient unswept oil displacement allowing us to save on the OPEX by maintaining decreased power consumption while reducing the acid/water requirement upto 10 times as compared to currently applied conventional EOR methods. This study takes one step forward towards the development of EK LCA-IOR method feasible for complex tight carbonate reservoirs in UAE.