Significant Oil Uplift from Field Implementation of the First High Salinity Polymer-Flood Targeting a Sour Heavy Oil Reservoir Worldwide

Abstract

A regular 5-spot pattern has been used to evaluate the techno-economic feasibility of polymerflooding after water-flooding using high salinity effluent water (up to 200,000 ppm TDS) for the Umm Niqa Lower Fars (UNLF) reservoir using a sulfonated synthetic polymer (Polymer A) that was selected based on extensive lab evaluation followed by a one-spot EOR pilot (Al-Murayri et al., 2020). Upon acquiring positive one-spot EOR pilot results, it was decided to proceed with a regular 5spot water-flooding/polymer-flooding pilot composed of 4 injectors, one producer, and one disposal well. Water-flooding started in 2021 and continued for approximately 1.5 years. After establishing a water-flooding baseline, polymer-flooding was initiated by late 2022. An integrated surveillance/monitoring protocol has been established including downhole pressure/temperature sensors, wellhead gauges, flowmeters, in-line viscometer(s), well logging, passive/partitioning tracer campaigns and detailed lab analysis of produced and injected samples. Besides lab analysis of produced samples, oil cut measurements have been regularly validated using a multi-phase flowmeter, a 3-phase separator and portable 2-phase separators. Water injection into UNLF was successfully implemented under sub-fracturing conditions. Tracer data indicated that two of the injectors are more connected to the central producer compared to the other two. A steep increase in water cut at the central pilot producer was clearly noticed reaching ~90% before the commencement of polymer-flooding. Approximately 0.55 PV of water was injected prior to polymer injection. The central producer has been producing since January 2016. Oil recovery from natural depletion and water-flooding is estimated to be around 23%. After polymer-flooding, water cut from the central pilot producer was reduced to 40% within 4 weeks. This favorable trend of oil cut increase continued, thus reaching a peak of ~70%, with a plateau between 60-65% after 3 months of continuous polymer injection. These field results are fairly in line with reservoir modelling forecasts and have been validated using 4 independent oil cut sources, namely: 3-phase separator, portable 2-phase separator(s), MPFM and on-site lab analysis. The strong water cut reversal trend that was observed post polymer-flooding unequivocally demonstrates considerable improvement in volumetric sweep efficiency and conformance control. Work is underway to acquire additional surveillance/ monitoring data to fine-tune the reservoir model and continue optimizing polymer-flooding techno-commercial feasibility. The acquired field results from UNLF polymer-flooding to this point demonstrate the feasibility of using high-salinity effluent water with customized sulfonated polymers to increase oil recovery from a shallow, sour and unconsolidated heavy oil sandstone reservoir. Field operations are in progress to gather high-quality data in preparation of a smooth and expeditious transition towards phased commercial polymer-flooding development.