The paper reports a best-practices case study regarding the Casing-while-Drilling (CwD) installation of large outer-diameter (OD) tubulars—30-inch casing, specifically—in a troublesome zone in Campeche Bay, Mexico. The 30-in. CwD job was an industry first for this pipe size. The installation was an ambitious attempt to drill a 30-in. conductor in an area historically fraught with extreme wellbore instability and to produce better results than conventional drilling could deliver.
Another objective was to push the 30-in. conductor to a depth that had been unattainable in previous instances of comparable lithology. Hammering was too disruptive for such a precarious formation, and conventional drilling, with its manual equipment and serial tripping, was too time-consuming, making well collapse probable. CwD, therefore, was the best option.
The CwD process entailed a 30-in. Casing Running Tool (CRT) with hydraulic pick-up arms and a remotely operated Single Joint Elevator (SJE) handling the casing, the first joint bearing a 34-in. drillbit. In one run, the 30 × 34-in. conductor section was drilled, cased, and cemented at a total depth of 256m—78m reaching/jetting into seabed, 178m drilling. The job only took 9.52h, with an average Rate of Penetration (ROP) of 18.04m/h, and drill-time was reduced by 1.31d (26.3%) when compared to conventional drilling. And there were no stuck pipe issues, problems while tripping in the hole, or safety incidents.
Successful completion of the well hinged on the CRT's multi-functionality and capacity for running large-OD tubulars. Filling, or pumping, the string while lowering served as a lubricator, evacuating cuttings more effectively and resolving the hole-cleaning inefficiencies experienced in adjacent wells. The improved running efficiencies were also realized due to the hydraulic arms enabling better control of pipe movement; more specifically, the operational benefits of superior handling of large-OD pipe were three-fold.
First, rotation of the string enhanced the plaster/smear effect, strengthening the wellbore, averting lost circulation, and minimizing formation damage. Second, the large casing-to-wellbore diameter ratio created a gauged well, the smoother, more circular profile contributing to better well stability and requiring less cement. Third, a small, mono-bore annulus (between wellbore and casing) and consequent higher annular velocity facilitated cutting transport, prevented wellbore erosion, and resulted in hydraulic optimization while running 256m of conductor.