Pump up the volume - Massive water injection increase through open water stimulations

This paper describes the evolution of subsea stimulation treatments within one field including a novel dual vessel approach that was developed and successfully implemented on multiple wells. The methodology that enabled stimulations of high volume, complexity and precision is described, including observed results and opportunities for continuous improvement. In a harsh low oil price environment such cost-efficient stimulations can unlock additional potential for many subsea developments. Three West of Shetlands (WoS) injectors stimulation campaigns successfully delivered 11 subsea well treatments with a novel dual vessel batch approach in 2020 delivering operations of outstanding efficiency and reservoir results while driving costs down. A construction vessel provided remotely operated vehicle (ROV) support including deploying the well control package, whereas the stimulation vessel ran its own downline to facilitate optimized use of its dedicated pumping system and large chemical handling capacity. To enable deep water stimulation, the quick connect downline was engineered and project specific equipment installed onto the stimulation vessel allowing deployment to 450m water depth. Notable cost reductions in excess of 34% were achieved utilizing the efficiency offered by manifold entry for batch treatments to minimise the number of subsea re-connection operations while the stimulation vessel allowed much larger bulk loadouts and optimised the number of vessel loadings for continuous operations. This novel dual vessel approach for batch subsea stimulations allowed multiple well access through 'daisy chains' within isolated pipeline segments, while keeping injection operations live to other wells from the Glen Lyon Floating Production Storage and Offloading Vessel (FPSO) in the Schiehallion field. Improved HSE performance was achieved through reduced chemical handling and transportation. Real time data solutions for onshore monitoring were developed which aided the management of COVID-19 risks. The post-stimulation injection rate from the stimulation has signifcantly improved in all wells, resulting in large additional injection capacity for the field. Maintaining increased injection capacity has proved to be a challenge. The acquired understanding regarding water quality and longevity of treatments will allow identification of further continuous improvement opportunities to enable sustainable stimulation results. © 2021, Society of Petroleum Engineers