Alkali Polymer Flooding: Tackling Risks and Challenges from Feasibility Study to Pilot

Abstract

Alkali Polymer (AP) is considered as enhanced oil recovery (EOR) technique for a mature field in Austria. To achieve technology qualification, different workflows have been implemented that supports risks definition and mitigations. We therefore present here the necessary steps utilized for the AP technology development and qualification. We evaluate challenges including laboratory assessments, subsurface and surface elements, aiming at demonstrating the effectiveness of AP to produce additional oil and to enable a field pilot. Multidisciplinary work packages allowed creating a holistic understanding of the benefits and challenges of AP injection and mitigate these challenges to enable a field pilot. Laboratory experiments were performed to determine an effective recipe to mobilize oil without detrimental reservoir interaction (rheology measurements, phase behavior tests, core floods etc.). The design of the pilot facilities built on water softening technologies tests. Finally key producers were identified based on previous tracer and polymer breakthrough results, and workovers were planned to allow implementing scaling mitigation solutions. A partitioning tracer test was also carried out to measure the remaining oil before AP pilot. The selected recipe showed significant residual oil mobilization, recovery factor increases and low polymer adsorption. Aging experiments showed that polymer hydrolysis in the reservoir in alkaline conditions allowed using lower polymer concentration and facilitate injectivity. Facilities design centered around keeping pilot costs as low as possible, by reusing existing polymer dosing and mixing facilities, and designing an additional alkali dosing and mixing plant. To mitigate the risk of precipitation at the injector, the water treatment was upgraded to remove divalent ions before mixing with alkali. Pre-qualification tests under field conditions allowed developing and optimizing a weak acid cation exchanger unit meeting operational requirements. This process was then engineered at the pilot scale and implemented in the AP pilot project. Finally, wells were evaluated to ensure material compatibility with AP fluids, and 3 producers with high expected alkaline back-produced concentration were selected for a workover allowing retrofitting a scale inhibition string. The scale inhibitor was selected using a dynamic scale loop. In conclusion, all work packages performed enable carrying out a field pilot with reduced risk. Starting Q2 2023, the pilot will focus on gaining operational experience with the new facilities, as well as scaling and emulsions mitigation solutions. While the industry saw multiple Alkaline, Surfactant and Polymer floods, Alkali and Polymer has only limited literature. However, by avoiding costs linked to surfactant, AP appears as an attractive EOR technique for highly reactive oils. This work presents the steps carried out to obtain understanding of the potential oil gains, and evaluate injectivity, scaling and emulsions risks. The methodology allowed de-risking the technology and bringing it from the laboratory to the field with a pilot.