Options for the Recycling of Drill Cuttings

Abstract

Abstract It is estimated that the UKCS produces between 50,000 to 80,000 tonnes wet weight of oily drill cuttings annually. With the implementation of OSPAR Decision 92, and given current offshore technology, it is no longer possible to discharge cleaned oily cuttings to sea. Increasingly stringent legislation also makes it likely that cuttings derived using water-based muds will not be discharged to sea in the future. Although several commercially available treatment processes can remove oil from oil based mud (OBM) cuttings, there are few satisfactory outlets for the residual solid material most of which currently goes to landfill. In light of the legislative changes, increased focus on duty of care, and commercial considerations, viable alternatives are being sought for the recycling and reuse of large volumes of material from future drilling programs. This paper examines possible options for converting drill cuttings into reusable secondary products and discusses the advantages and disadvantages of each option when considered against the criteria of environmental impact, technical risk, logistics, liability and cost. Examples of the research and pilot trials currently being undertaken to assess the feasibility of these options is discussed, as well as work being carried out to establish the variation in chemical composition of cuttings in the UKCS, since tolerance to the variation in the chemical characteristics of drill cuttings is a major issue for most of the end uses. Introduction Under present OSPAR legislation, oil based mud (OBM) cuttings bearing more than 1% oil-on-cuttings by weight cannot be discharged to sea. To date, technology cannot provide cost-effective, large volume cleaning offshore to these levels. Contaminated cuttings are therefore returned to shore uncleaned, for treatment and/or disposal. Operators, and their waste management contractors, are therefore faced with a considerable waste handling and disposal issue. Current estimates suggest of the order of 50,000 tonnes of OBM cuttings are produced in the UKCS annually. OBMs are essential in present practices for drilling certain sections of wells and in certain rock formations, and there is little prospect that they can be phased out entirely. Re-injection appears practical in some 25% of well developments however larger volumes of WBM may be returned to shore as environmental aspirations increase. There are several onshore operations providing a facility for reducing the oil content of OBM cuttings. The most common treatment technique used in the UK at present is indirect thermal desorption. This process removes oil and water from cuttings and has two objectives:to bring the oil content under the Special Waste classification threshold, andto produce a more easily handled dry product. There appears to be no developed, large-scale outlet for the recycling of the treated material. Consequently, the bulk of treated cuttings are disposed of in landfill sites. This paper addresses the management of cuttings from future drilling operations in the UKCS from the perspective of sustainable development, identifying options that are commercially and technically feasible for recycling and/or disposal. The approach taken was holistic in that the life cycle of the "product" was considered, taking account of secondary products and emissions. Options were identified to either recycle drill cuttings either as an addition to, or replacement for, a raw material that was required for the manufacture of a product or material; or as a supplement to an existing feedstock of waste material, that was already being processed into a useful product. The term "recycling" has been adopted, as the aim was to recycle drill cuttings into the chain of utility rather than re-use the cuttings as drill cuttings. Although the study looked at geographically widespread solutions, there was a locational emphasis on the Aberdeen area, where the majority of cuttings are brought onshore.