Continuous circulation drilling technology has been used significantly in the Mediterranean during both shallow and deepwater offshore applications to address various drilling challenges. Continuous circulation is a variant of managed pressure drilling (MPD) in which mud pumps remain on, thus providing constant circulation of drilling fluid downhole through the wellbore and up the annulus during the process of adding and/or removing stands of drillpipe.
From 2014 to January 2019, the continuous circulation system was successfully deployed in offshore Egypt on 20 wells, totaling more than 1,785 successful continuous circulation drillpipe connections. During the same 5-year period, two offshore wells in Cyprus were drilled, adding more than 305 continuous circulation connections. This followed a separate extended campaign from 2006 to 2012 that used continuous circulation technology to drill 13 wells.
The use of continuous circulation to drill on both fixed platform and floating vessels in the Mediterranean has provided a solution for navigating tight drilling windows. For example, this technology was used during the exploratory phase of a project, which assisted an operator in reaching total depth (TD). This project resulted in the discovery of a significant natural gas field, where operation continues to this day.
Overall, lessons learned from the work in the Mediterranean include continuous circulation providing enhanced hole cleaning and improving cuttings transport efficiency, which helped in mitigating stuck pipe incidents in an extremely long horizontal section. In wells with extremely narrow drilling windows, continuous circulation was used in conjunction with standard backpressure-control MPD to provide an enhanced level of control and automation. In other wells, 8-in. continuous circulation subs were deployed to provide the capability for a 1,200-GPM circulation rate. Between drilling campaigns, onsite repair, maintenance, and recertification activities reduced transport costs and allowed the system to remain prepared for further operation.
With the combination of a proper drilling fluid design and continuous circulation during drillpipe connections, the operator can maintain a constant bottomhole pressure (CBHP) necessary to navigate wells with a narrow pore pressure and fracture pressure margin. By eliminating the large pressure swings caused during conventional drilling when cycling the pumps on and off, influx or fluid loss situations can be reduced or eliminated.
With a long and positive history, continuous circulation technology has helped eliminate a variety of drilling challenges by increasing operational efficiencies and reducing overall nonproductive time (NPT), all leading to a reduction in drilling days, and therefore, operator costs.
