Drilling operations can require the usage of oil base drilling fluids (OBM). These fluids are formulated as an emulsion consisting of water emulsified into a continuous oil phase. During the last decade the North Sea drilling industry has moved from using diesel oil to low toxic base oils in OBM. Further development of low toxic base oils has continued on the Norwegian Sector of the North Sea, and resulted in the use of non-aromatic base oils. The current paper describes the results from a field test where the introduction of non-aromatic base oils reduced the hydrocarbon content by more than 50% in head space level in the shale shaker area compared to the use of low toxic base oils. In this test two wells were drilled where the hydrocarbon vapour and mist were collected at the same locations in the shaker area. The first well was drilled with a more traditional low toxic mineral oil based drilling fluid. The second well was drilled in a comparable formation with a drilling fluid based on the non-aromatic base oil. The paper also describes how skin irritation is reduced when using the non-aromatic base oils compared to the use of previous base oils and synthetic base oils. The reduction in skin irritation and hydrocarbon content at head space level has significantly improved the occupational hygiene for personnel exposed to drilling fluids offshore. The paper also discusses biodegradability and toxicity of different base oils. Ecotoxicological test results indicate that use of the non-aromatic base oils may result in less environmental impact compared to use of other mineral oils or synthetic oils if an accidental discharge occurs. Finally, the paper discusses dermal irritation effects from the different drilling fluids. It is shown that use of the non-aromatic base oil reduces the skin irritation index compared to use of other oil or synthetic base oils. Introduction During a period in the fall of 1997 a well was drilled with used low toxic mineral oil based drilling fluid (LTOBM) on a field on the Norwegian sector of the North Sea. On a comparative well drilled in the spring 1998, the OBM was based on non-aromatic base oils (NAOBM). The hydrocarbon content in the air at head space level was measured at the same locations at those drilling operations. Both of the OBMs were used; thus leaving the OBMs slightly polluted by reservoir oils. The pollution by reservoir oils is anticipated to have only limited effect on the overall occupational hygiene and environmental properties of the OBMs. Before proceeding it is important to define the term non-aromatic base oil. Non-aromatic is meant to describe an oil without any measurable content of poly-aromatic hydrocarbons. Other types of hydrocarbons containing cyclic compounds are not described by the term aromatics in the present context. Accidential spills of OBM can occure. Therefore it is important to outline how big an impact the OBM will have on the marine environment compared to synthetic based fluids like Ester based drilling fluids or linear alphaolefine based drilling fluids since cuttings drilled out with the latter drilling fluids can be permitted. Inhalation of oil mist and oil vapour may lead to irritation of the mucous membrane and the respiratory organs. Aspiration of oil may lead to chemical pneumonia. The most commonly reported health effects reported due to inhalation of oil mist or vapour are acute effects, such as headache and nausea. Long term health effects such as cancer or reproductive effects has not yet been proven. However, precautions are taken within the industry to avoid these problems by selecting acceptable base oils for oil based drilling fluids.
The new OSPAR regulation (OSPAR 2000/3) on drill cuttings is due to be effective by January 2005 at the Norwegian continental shelf. Drilling operations planned to be performed from to date and onwards therefore have to take into account that the forthcoming regulation has important implications with respect to selection of adequate and compliant technology. Drilling will commence at a new HTHP Statoil operated field offshore middle Norway, by late summer 2003. Ahead of the spudding in, a detailed and comprehensive review of technological solutions has been carried out to resolve the issues of zero discharge and use of best available technique. The paper describes the challenges associated with the forthcoming zero discharge regulation and the different technological scenarios that have been reviewed. Waste minimisation methodology has been of major importance in the decision process. Treatment of oily drilling waste, applying new technology at the rig, was studied in detail. The respective energy budgets, environmental impacts and risks associated with the different solutions are also presented, as well as a suggested best technique. The paper offers a study of how operators may comply with a zero discharge in drilling operations, with reference to BAT (best available technique). On a general basis the ultimate goal of environmental legislation is discussed with reference to the forthcoming discharge regime and how to decide BAT; achieving the right balance between technology and value. Introduction Statoil ASA is the operator of a sub-sea high temperature high pressure (HTHP) gas and condensate field offshore mid-Norway. Due to increasingly tighter legislation and regulations with respect to discharges and emissions during drilling operations applied drilling and waste technologies must be of a high standard. Further, for confidence building preferred technological solution should be accompanied by a transparent decision making procedure, allowing insight for any stakeholder. Recognizing that no common acknowledged formula exists, e.g.: a discriminative instruction for deriving at an exact solution, decisions related to drill cuttings disposal have to be weighted up against several adequate issues. The new OSPAR regulation (1) on drill cuttings is due to be effective by January 2005 at the Norwegian continental shelf. The zero discharge regime will then prevail. The planned drilling operations aspire to comply with this regime. A European Council Directive (2), the "IPPC Directive" is also important, as a secondary legislation adopted to pursue a certain purpose within a given hierarchy and legal framework. Of particular interest is how this Directive addresses the concept of new technology aiming to qualify as best available under the terms of the Directive (BAT = Best Available Technique). The "integrated approach" pursued under the IPPC Directive is essential as it addresses the problem of a number of highly undesirable environmental impact "transfers" that resulted from previous discrete, source specific legislation:"shifting of pollution" from one media to another,shifting of pollution between different geographical areas,and the replacement of pollution emissions by increased energy and/or material consumption. Balancing zero discharge and BAT is by no means straightforward. In order to comply with the new legislation and regulation a detailed and comprehensive review of technological solutions was carried out to resolve the issue of zero discharge and use of BAT. As will be presented a new offshore waste minimization technology, a hammermill unit (TCC) capable to treat drilling waste at the drilling rig was evaluated as a possible BAT. This technology in many respects intensifies the discussion about right or wrong decisions, and therefore the implication of this technology is given particular attention. Is a literally zero discharge regime justified, and can it be defended against the renunciations it apparently encompasses? This is an intriguing question that tickles the wits of stakeholders.
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