Polymer Flooding Reduces Emissions and Energy Consumption in the North Sea

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 218231, How Polymer Flooding Reduces CO2 Emissions and Energy Consumption at the Captain Field: An Exergy-Return-on-Exergy-Investment Case Study,” by Tormod Skauge, SPE, and Arne Skauge, SPE, Energy Research Norway, and Nancy Lugo, Ithaca Energy UK, et al. The paper has not been peer reviewed. _ Insights into the energy efficiency and environmental performance of the extraction of heavy oil from the Captain field in the UK sector of the North Sea are gained using life-cycle assessment (LCA), which incorporates the concept of exergy-return-on-exergy-investment (ERoEI). The LCA allows for separation of the process into material and work streams, assessing the effect of each separately. In the complete paper, the authors compare waterflooding (WF) to polymer flooding (PF) as primary extraction strategies. Introduction The Captain field is approximately 145 km northeast of Aberdeen, Scotland. The reservoirs lie at shallow depths of approximately 900 m true vertical depth with correspondingly low temperatures of 31°C and low pressures of 87 bar. A primary challenge is the relatively viscous oil of 40–140 cp. The field was initially developed with long horizontal wells and downhole pumps. Viscous oil implies mobility challenges, however, and water injection could lead to unstable displacement, early water breakthrough, and possible coning issues. After a successful pilot PF at Captain during 2010–2017, a staged enhanced oil recovery (EOR) development approach was adopted in 2016 aiming to extend the pilot polymer-solution-injection scheme to the full field through a phased development. Following the pilot study, the Captain EOR project was split into Stage 1 and Stage 2. The first stage involved drilling of five producers and two EOR injectors by 2022. The second stage included some brownfield modifications across the three Captain installations (two installations and a floating production, storage, and offloading vessel) and a significant expansion in the subsea area. The complete paper concentrates on the expansion in the subsea areas, Areas B and C. The methodology of the study, including the development of simulation cases, LCA, exergy analysis, system boundaries, material and work streams, and CO2 emissions, is detailed in the complete paper. Production Profiles The Stage 2 EOR development evaluates PF for Areas B and C. The baseline is WF with fully produced water reinjection. WF was scheduled to begin in January 2024 and to end in December 2099. The PF case also was slated to begin in January 2024 and to end in 2035 and 2034 for Area B and Area C, respectively. The field is operated on pressure maintenance, and the voidage replacement ratio is kept close to 1.0. This means that the PF injects more liquid than the WF case during the first 5 years of injection when the oil production is higher for PF. After polymer injection ends, the PF case injects less liquid than the WF case. In Area B, water cut is high from the start for the WF case. Because of the high mobility of the water, it fingers through the oil. In contrast, when polymer is injected, the water cut falls to approximately 80% and does not reach the starting value of 94.1% before 7 years, more than 2.5 years after having stopped the polymer injection in this area. The low water cut is the result of production of a large oil bank generated by the improved sweep and mobility reduction of the injected polymer.