Integrated Approach to Analyze the Compatibility and Performance of Electrokinetic Low-Concentration Acid IOR in Heterogeneous Abu Dhabi Carbonate Reservoirs
Authors: Ansari Arsalan A. , Haroun Mohammed , Rahman Mohammed Motiur , Chilingar George V. 
Published: March 2016

The increasing global demand for additional energy requirement forecasted upto 74% in 2030 has made Improved Oil recovery (IOR) at the forefront of oil and gas R&D for the past 4 decades as it helps in the improvement of the hydrocarbon sweep efficiency. In carbonate reservoirs, there is a challenge of having large fractions of unswept oil, mainly due to permeability damage, heterogeneous formation or unfavourable petrophysical properties. Conventional acidizing, though useful in increasing the effective permeability in the near well-bore region, has issues of limited depth of penetration, as acid is consumed and adsorbed early into the formation. However, the application of Electrokinetic Low-concentration acid IOR (EK LCA-IOR), where conventional low-concentration acidizing (LCA-IOR) is coupled with electrokinetic enhanced oil recovery (EK-EOR) [Ansari et al., 2014], has resulted in targeting the previously immobile oil, significantly improving the capillary number while minimizing acid consumption and adsorption.

This study demonstrates an integrated approach using Single Energy Computed-tomography (SECT) scan imaging and Nuclear Magnetic Resonance (NMR) to analyze the compatibility and effectiveness of EK LCA-IOR in carbonate reservoirs through an increase in depth of penetration. Core-flood experiments at Abu Dhabi reservoir conditions conducted on 1-foot core-plug, involved waterflooding followed by LCA-IOR, assisted by electrokinetics in both sequential and simultaneous fashion, identifying optimum conditions (1.2% HCl concentration, 1V/cm voltage gradient).The use of SECT images of core-plug before and after the experiments, confirmed wormhole orientation and propagation length across heterogeneous core-plugs. NMR was used to identify and confirm various reservoir rock types (RRTs)that were tested allowing us to expand the range of optimum current densities and acid concentration for the EK LCA-IOR process to meet the objectives of this study in maximizing displacement efficiency and permeability enhancement.

Findings confirm EK LCA-IOR application resulted in additional 15–35% displacement efficiency beyond the waterflooding limit (60%). In addition, the maximum permeability enhancement of 53% was recorded and made possible using the simultaneous approach. SECT imaging confirmed that the maximum penetration depth of the injected acid was achieved using the simultaneous approach as the enhancement of depth of penetration was 82% and 70% in simultaneous and sequential approach, respectively. Furthermore, NMR results indicate that EK LCA-IOR is promising across heterogeneous formations, which allows us to optimize the process for each unique formation, using the identified operating parameters increasing displacement efficiency by 35% and permeability enhancement by 28%.

EK LCA-IOR may be developed as an environomic technology targeting the reduction of power consumption and acid/water requirement upto 70% as compared to conventional IOR processes. This study takes advantage of integrating imaging capability of SECT & NMR in order to couple particle mobility and zeta potential to assess the performance of EK LCA-IOR compatibility in Abu Dhabi carbonate reservoirs.