Summary Annular reinjection offers a cost-effective disposal mechanism for the oily cuttings and associated wastes generated when oil-based muds are used during drilling. This disposal method eliminates overboard cuttings discharge and hence removes any environmental impact. Continued use of oil-based muds is therefore feasible. A 12-member Drilling Engineering Assn. in Europe (DEAE) project was initiated in 1990 to study the engineering aspects of this approach in the North Sea. This paper reports on the first trial off a fixed platform in the North Sea and discusses the preliminary engineering studies, injection, and analysis of fracture propagation. It demonstrates that, with proper regard to the engineering of the injection well, the process is a safe, efficient, and effective disposal technique. Introduction Low-toxicity oil-based muds (LTOBM's), used widely in the North Sea operating area, offer significant operational benefits, especially for exploration and appraisal drilling and, more importantly, for development drilling. However, the overboard discharge of the oil-contaminated cuttings leads to environmental damage that, although localized, is unacceptable. To resolve this conundrum, novel water-based muds were evaluated and a range of cleaning and disposal options for the cuttings was reviewed. From these options, cuttings slurrying and reinjection appeared to offer the most cost-effective solution because this approach would also address the problem of oily liquids from the drilling unit. Cuttings slurrying and reinjection is established practice in Alaska and the Gulf of Mexico, but the technique had not been used previously in the North Sea. We knew that the legislative authorities would have some concerns. Therefore, 12 operating companies sponsored a joint project, through the auspices of the DEAE, to evaluate the engineering issues associated with this approach. The project was established with three objectives in mind:to demonstrate that cuttings slurrying and reinjection was technically viable for the North Sea,to gain acceptance of this approach to waste management from North Sea legislative authorities, andto evaluate a novel approach to cuttings grinding.

This paper describes how Conoco planned and implemented downhole injection of oil contaminated drill cuttings on the

No abstract