Abstract

A thorough review of past chemical EOR projects illustrate that chemical EOR implementation can result in produced-fluid handling issues. However, in all projects such issues were resolved, mainly through a combination of improved demulsifiers and oversized vessels. In previous work, we have demonstrated the potential of surfactant/polymer flooding for a high temperature and high salinity carbonate. In lieu of future plans to pilot the process, further assessments were conducted to evaluate any side effects of those EOR chemicals on upstream facilities and come up with mitigation plans if needed. In this work, we investigate the surfactant-polymer compatibility with additives used in processing facilities for demulsification, and scale and corrosion inhibition as well as their possible impact on oil/water separation and metal corrosion.

We firstly conduct a sensitivity-based simulation study to estimate the volumes of back-produced EOR chemicals. Secondly, a comprehensive compatibility study were conducted to evaluate EOR chemicals compatibility with oilfield additives (i.e. demulsifier, corrosion inhibitor, and scale inhibitor). Bottle tests were also conducted using surfactant-polymer solutions prepared in both injection and produced water to evaluate EOR chemicals impact on oil/water separation. Separated water qualities were evaluated using solvent extraction followed by ultraviolet visibility testing. Finally, static and dynamic corrosions tests were performed to evaluate EOR chemicals possible side effects.

Based on simulation, the peak polymer and surfactant concentrations at the separation plant would be 83, and 40 ppm, respectively. The sensitivity study suggests a worst case scenario in which peak polymer and surfactant concentrations of 174 and 128 ppm are back-produced. Comprehensive compatibility testing confirmed the compatibility of EOR chemicals with the additives used in upstream facilities. In those tests, neither precipitation nor phase separation were observed. Bottle tests indicated an overall negligible impact on oil/water separation speed. However, analyses of separated water quality indicated a noteworthy deterioration in separated water qualities. Oil-in-water concentrations increased from 100 to 750 ppm and from 300 to 450 ppm at injection and produced-water salinities, respectively. Finally, corrosion tests suggest surfactant-polymer presence results in a significant reduction in corrosion rates by 70 and 86% at static and dynamic conditions without any pitting issues.

Based on those results, the selected surfactant-polymer implementation will have negligible impact on separation facilities, if any. The main side effect was on oil/water separation. However, we shall stress that, at produced-water salinities, gravity-settling rates were not affected; yet, a slight but manageable deterioration in separated water quality was observed. However, a slightly more pronounced impact on separation could be observed at a late stage of the pilot once the polymer overflush (hence only polymer without surfactant) is back-produced. Nonetheless, we believe, such side effects if any can be addressed by adapting the demulsifier dose rate and will probably be small due to the reduction in polymer backflow concentrations at later stages and the continuous degradation of the polymer at reservoir high temperatures.

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