Continuous Circulation Technology to Reduce Drilling Days in Offshore West Africa: Case Study

Continuous circulation technology is a form of managed pressure drilling (MPD) where the constant circulation of drilling fluid is maintained by allowing the rig pumps to remain on while adding and removing stands of drillpipe. Using continuous circulation, many drilling challenges are solved through continuous hole cleaning and solids transport, including maintaining constant bottomhole pressure (BHP), reducing the loading of solids and cuttings bed formation resulting from a pumps-off state, mitigating stuck pipe incidents, reducing ballooning effects, providing continuous cooling of bottomhole assembly (BHA) components, and improving formation integrity. Continuous circulation technology was used extensively for its hole-cleaning benefits during a 17-month development, gas drilling, and oil drilling campaign on a deepwater drillship in offshore West Africa from 2015-2016. Operations restarted in 2018 and are ongoing in 2019. Deepwater drilling using continuous circulation in this field provided a solution for significantly helping improve the rate of penetration (ROP) through continuous hole cleaning when drilling one stand per hour or faster. With constant circulation during the drillpipe connection process, the operator was able to significantly decrease the amount of time spent on hole-cleaning activities after a stand was drilled down in both oil-based mud (OBM) and water-based mud (WBM) applications. The enhanced hole cleaning provided by continuous circulation also helped improve cuttings transport efficiency, mitigate stuck pipe incidents, and enhanced the ability to drill a clean hole. This continuous circulation system was used on a deepwater drillship in offshore West Africa on 16 wells from 2015-2016, following two wells drilled without this technology, and four wells after the restart in 2018. Overall, more than 535 operating days and more than 1230 successful continuous circulation drillpipe connections were performed during both drilling and tripping operations. Because of the increased ROP provided by continuous hole cleaning with the system, approximately five drilling days were saved per well, totaling to an approximate 85 drilling day reduction over the planned drilling campaign from 2015-2016, resulting in a significant cost savings to the operator and to obtain first production much sooner than anticipated. Continuous circulation technology has proven to reduce overall nonproductive time (NPT) and total drilling days. During a long-term drilling campaign, additional improvements were recognized with superior prewell planning and front-end engineering design to minimize interference with rig operations and equipment and improve understanding and communication between the service company and operator. A newer generation, dual-activity rig helped prevent downtime by providing a platform for continuous repair and maintenance activities while drilling.