The effect of drilling fluid base-oil properties on occupational hygiene and the marine environment

Drilling operations can require the use of oil-based drilling fluids (OBM). These fluids are formulated as an emulsion consisting of water emulsified into a continuous oil phase. During the past decade, the North Sea drilling industry has moved from using diesel oil to low-toxic base oils in OBM. Fu rther development of low-toxic base oils has continued on the Norwegian sec tor of the North Sea and has resulted in the use of nonaromatic base oils. This paper describes the results from a field test in which the introductio n of nonaromatic 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-t oxic base oils. In this test, two wells were drilled in which the hydrocarb on vapor 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-b ased drilling fluid. The second well was drilled in a comparable formation with a drilling fluid based on the nonaromatic base oil. The paper also des cribes how skin irritation is reduced when using the nonaromatic base oils, compared to the use of previous base oils and synthetic base oils. The paper discusses biodegradability and toxicity of different base oils, E cotoxicological test results indicate that use of the nonaromatic base oils may result in less environmental impact, compared to the use of other mine ral oils or the synthetic oils used in Nor-way, if an accidental discharge occurs. Finally, the paper discusses dermal irritation effects from the different d rilling fluids. It is shown that use of the nonaromatic base oil reduces th e skin irritation index compared to use of other oil or synthetic base oils .