Deepwater Blowout—A Case History: Shallow Gas Hazards Hide in the Weeds

Abstract

Abstract This paper will detail the sequence of events involving the blowout of a deepwater development well adjacent to the discovery well, while Loop Current prevented running of the BOP stack and riser following the cementing of surface casing. Water depth was 2,400ft. The cause of the blowout was gas flow after cementing. The operator designed the discovery well to incorporate the pump and dump process and successfully drilled riserless through a shallow gas hazard. Surface casing was run and cemented and the #1 well drilled to the objective depth and completed, pending field development. The operator spudded the #2 well less than 200ft from the #1 well and duplicated the process, drilling riserless through the shallow hazard and running surface casing. After circulating lead cement to the mud line and observing cement returns at the wellhead, a proprietary cement slurry designed to achieve "right-hand set profile" was circulated into the well as planed. The drill string was withdrawn and preparations were made to run the subsurface stack and riser. However, Loop Current developed and prevented the running of any equipment until the currents subsided. Almost three weeks elapsed before the Loop Current abated, at which time the ROV was deployed and discovered the blowout. The plume of the blowout carried over 300ft. This paper will chronicle the extensive effort which the operator expended to reenter the well, perforate, pump kill mud, confirm that the well was static and cement. The conclusion however, is somewhat surprising: three days dormant after cementing the #2 well, while drilling the replacement well, the #2 blew out again. The paper will also present solutions implemented to successfully drill the replacement well.