Polymerflood Field Pilot Enhances Recovery of Heavy Oils on the Alaska North Slope

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201279, “First-Ever Polymerflood Field Pilot To Enhance the Recovery of Heavy Oils on the Alaska North Slope: Producer Responses and Operational Lessons Learned,” by Samson Ning, SPE, Reservoir Experts and Hilcorp Alaska, and John Barnes, SPE, and Reid Edwards, SPE, Hilcorp Alaska, prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, 5-7 October. The paper has not been peer reviewed. The complete paper describes a field pilot project to perform an experiment to validate the use of an advanced polymerflooding technology on the Alaska North Slope. Polymer injectivity of horizontal wells is found to be sufficient to replace reservoir production voidage, although some declines occurred as high-viscosity polymer swept the near-wellbore region. Production data show significant reduction in water cut and increase in oil production rate. No polymer production has been confirmed from the two horizontal producers after 23 months of polymer injection into the two supporting horizontal injectors. Introduction The pilot involves two horizontal injectors (J-23A and J-24A) and two horizontal producers (J-27 and J-28) drilled into the Schrader Bluff NB sand in an isolated fault block of the Schrader Bluff heavy-oil reservoir in the Milne Point field. The lengths of the horizontal wellbores range from 4,200 to 5,500 ft, and the interwell distance is approximately 1,100 ft. Hydrolyzed polyacrylamide (HPAM) polymer injection began on 28 August 2018 using a custom polymer mixing and pumping unit. Polymer-solution quality control is discussed in detail in the complete paper. Injector Performance Since the start of polymer injection, a few shutdown events have occurred that lasted longer than 2 weeks. The first major shutdown took place in September 2018, when a more-than-expected amount of hydrocarbon gas was detected from the source water used to make the polymer solution. The polymer-injection facility was shut down for 3 weeks to modify the pressure-letdown module for operation safety. The second major shutdown occurred in November 2018 for pump and auger repairs. The third major shutdown happened from mid-June through late August of 2019 because of polymer-solution-quality issues. After 2 months of diligent work, the polymer-hydration problem was resolved and improvements made in polymer facilities, operational procedures, and the onsite quality-control process. Polymer-injection operations have been smooth since August 2019 except for a few short shutdowns for equipment maintenance. As of late May 2020, total cumulative polymer injected was 708,000 lbm into the two injectors, and the total amount of polymer solution injected was 1.4 million bbl, approximately 8.8% of the total pore volume in the two flood patterns. Since polymer injection began, injected polymer concentration was mostly between 1,500 and 2,000 ppm to achieve a target viscosity initially set at 45 cp and then reduced to 40 cp.