The Effect of Drilling Fluid Base Oil Properties on the Occupational Hygiene and the Marine Environment

Abstract

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 Effect Of The Synthetic- And Oil Based Drilling Fluid's Internal Water Phase Composition On Barite Sag

“…If invert emulsion drilling fluids are used, the drilling fluid must be based on non-aromatic base fluids. 18 It is not possible to deposit oil-wet drill cuttings on the seabed. Re-injection of drill cuttings into the subsea formation or to ship it to shore for treatment, are therefore the only possible options.…”

Occupational exposure to airborne contaminants during offshore oil drilling

“…2 Although oil companies have their own surveillance programs, scientic publications presenting data on occupational airborne exposure during oil drilling are sparse. [3][4][5][6] These publications have shown that the total hydrocarbon air concentrations based on personal samples collected from the North Sea oil elds, are ranging from 10-200 mg m À3 at the drill oor and from 20-450 mg m À3 in the shaker area in the late 1980s. Later studies indicated oil mist air concentrations below 1 mg m À3 in personal samples.…”