Choose a Different Path. The Application of Multiple Activation Circulation Subs in Split Flow Mode to Assist with Hole Cleaning by Increasing Total Flow Rate in the Mariner Field, North Sea, United Kingdom

Abstract On the Mariner field in the United Kingdom sector of the North Sea, flow rate limitations imposed by well design and Bottom Hole Assembly (BHA) components restricted the ability to maintain sufficient annular flow velocity for effective hole cleaning, especially in the reservoir section. To address this challenge, a multiple activation circulation sub has been incorporated into the drill string and set-up differently - not to fully isolate the BHA below, as would be considered conventional use - but configured to direct a predetermined portion of the flow through the BHA while diverting the remaining flow into the annulus; a technique known as split flow. This paper analyses the outcomes and results of applying split flow hydraulics in two different hole sections on the Mariner field and demonstrates how the use of this split flow enabled higher overall flow rates, higher annular velocities, greater control over hydraulic performance and improved hole-cleaning efficiency by choosing a different path for the drilling fluid. The successful use of this technology helped the engineering team to trust this well design and continue to focus on improving other important aspects of the well design. The proof of this concept delivered significant cost savings on each well and is expected to continue to deliver for future wells on the field.