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

Abstract

Summary 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. Further development of low-toxic base oils has continued on the Norwegian sector 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 introduction 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-toxic base oils. In this test, two wells were drilled in which the hydrocarbon 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-based drilling fluid. The second well was drilled in a comparable formation with a drilling fluid based on the nonaromatic base oil. The paper also describes 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. Ecotoxicological test results indicate that use of the nonaromatic base oils may result in less environmental impact, compared to the use of other mineral oils or the synthetic oils used in Norway, if an accidental discharge occurs. Finally, the paper discusses dermal irritation effects from the different drilling fluids. It is shown that use of the nonaromatic 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 low-toxic, mineral-oil-based drilling fluid (LTOBM) on a field in the Norwegian sector of the North Sea. On a comparative well drilled in the spring of 1998, the OBM was based on nonaromatic 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 OBM's were used, thus leaving the OBM's slightly polluted by reservoir oils. The pollution by reservoir oils is anticipated to have only a limited effect on the overall occupational hygiene and environmental properties of the OBM's. Before proceeding, it is important to define the term "nonaromatic base oil." Nonaromatic is meant to describe an oil without any measurable content of polyaromatic hydrocarbons. Other types of hydrocarbons containing cyclic compounds are not described by the term "aromatics" in the present context. The aromatic content measured by UV analysis indicates that the low-toxic base oil had an aromatic content of less than 5 wt%, while the aromatic content of the nonaromatic base oil was less than 0.01 wt%. A typical aromatic content value was estimated to be 0.003 wt%. Accidental spills of OBM can occur. Therefore, it is important to outline how great an impact the OBM will have on the marine environment, compared to synthetic-based fluids such as ester-based drilling fluids or linear alphaolephine (LAO)-based drilling fluids, because cuttings drilled out with the latter drilling fluids can be permitted in some cases. In the following, only synthetic drilling fluids used in Norway will be discussed. Inhalation of oil mist and oil vapor 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 vapor are acute effects, such as headache and nausea. Long-term health effects such as cancer or reproductive effects have 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. Field Measurements To investigate the effect of base-oil properties on occupational hygiene, a field evaluation was conducted. The field evaluation consisted of four series of measurements for each OBM. Active sampling techniques using filter for oil mist and absorbents for oil vapor were performed with a PVC filter and a charcoal absorbent in series for both the stationary and the personal measurements. The PVC filters were extracted with Freon 113 and analyzed with infrared spectroscopy (IR). The charcoal absorbents are desorbed with carbon disulphide and analyzed by gas chromatography-flame ionization detector (GS-FID). Pumps are set for an air flow of 1.4 l/min, and air-flow control is performed at the start and end of each series of measurements. Each series had a duration of 1 hours; this period was chosen to optimize data quality because the time is long enough to collect data, and the time is also short enough to prevent the evaporation of the mist in the probes. The hydrocarbon threshold values for the combined sampling and analysis are 0.1 mg/m3 for mist measurements and 0.03 mg/m3 for the vapor measurements. The overall uncertainty is 10% of reported value for both the mist and vapor measurements. The hydrocarbon content and oil mist were collected at four measurement points. The drilling rig was equipped with four shakers. The first measurement point, Point A, was positioned at head space level between two of the shakers on the walkway in front of the shakers. The second point, Point B, was located at head space level above the flow channel for drilling-fluid sample collection, between two of the shakers. Point C was located at the work table for repair of shaker screens. The last measurement probe, labeled Point D, was carried by a person working in the drill floor area. The positions of the three fixed measurement collection points are shown schematically in Fig. 1 . All the measurement points are located in positions relevant to the daily exposure of personnel working in the drilling-fluid area or in the vicinity of that area. None of the measurement points was located inside special protection gears mounted to prevent vapor or mist from escaping to other parts of the rig. Thus, the measurement points span the typical working area for drilling-fluid personnel.

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.…”

Survival and gill morphology of different life stages of Tilapia guineensis exposed to the drilling fluid XP-07

“…SAASEN et al (2001) gave Median lethal concentrations (LC 50 ) of drilling fluids based on non-aromatic oil based muds (NAOBM) as (in mg l -1 ): >100,000, 576, 76,088 and 1211 for marine algae -Skeletonema costatum; mussel -Abra alba; copepod -Acartia tonsa and amphipod -Corophium volutator respectively. NEFF et al (1981) exposed 11 marine invertebrates to different drilling fluids and observed that the drilling fluids were acutely toxic to these organisms and the level of toxicity depended on the additives used.…”