Deepwater Blowout: A Case Study

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 105914, "Deepwater Blowout - A Case History: Shallow Gas Hazards Hide in the Weeds," by William Flores Jr., John B. Garner, SPE, and Chris Scarborough, SPE, Boots & Coots, prepared for the 2007 SPE/IADC Drilling Conference, Amsterdam, 20-22 February. The paper has not been peer reviewed. The full-length paper details the sequence of events of a blowout in 2,400-ft water depth of a deepwater development well adjacent to the discovery well. Loop current prevented running the blowout-preventer (BOP) stack and riser after cementing surface casing. After 3 weeks, the loop current abated, and a remotely operated vehicle (ROV) could be deployed. Upon deployment, it was discovered that the development well was blowing out, with the blowout plume carrying more than 300 ft. Introduction The prospect was drilled initially in 1997 and abandoned as a result of economics at that time. In the course of planning, a shallow gas hazard was identified from seismic, and records from the 1997 well reported several nonproductive days fighting lost circulation and gas. To avoid the nonproductive time encountered on the 1997 well, the operator designed a casing program for the first development well to include riserless drilling of the shallow gas hazard using the pump-and-dump process. Development Well 1 was drilled successfully in this manner and was completed as a producer in April 2006. The well currently is shut in, awaiting field development and production facilities. The rig was moved to a second location. Well 2 was spudded on 3 April 2006 less than 2,000 ft from Well 1 and drilled riserless through the shallow hazard. Structural pipe was jetted to 2,778 ft, which is 285 ft below the mudline. The 30-in. casing was allowed to soak for 4 hours. A 24-in. hole was drilled to 3,200 ft using seawater and gel sweeps. From 3,200- to 3,899-ft total depth (TD), a pump-and-dump system was used, maintaining a 10.5-lbm/gal equivalent mud density, by monitoring equivalent circulating density (ECD) with pressure-while-drilling (PWD) instrumentation and vortex mixing 16.0-lbm/gal water-based mud "on the fly" with seawater. A wiper trip was attempted. However, the well appeared to begin to flow with pipe at 3,597 ft. The pipe was tripped to bottom where circulation was begun and the equivalent mud weight (EMW) was increased to 10.7 lbm/gal. Circulation was stopped, and the well was observed to be static. A wiper trip then was made without problems. With no fill on bottom, the well was circulated again with a 10.7-lbm/gal EMW. While keeping the hole full, the pipe was pulled out of the hole to run 20-in. casing. The well, standing full of mud, was monitored by an ROV while preparing to run casing.