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Oil-based drilling fluids are essential for challenging drilling operations. However, their use requires costly handling, treatment and disposal. Supercritical fluid extraction is herein investigated as a novel technology to treat this waste. Supercritical fluid extraction employs a substance above its critical temperature and pressure as a solvent. In this state, the substance has both liquid- and gas-like properties that can be controlled by the pressure and temperature of the extraction process. In this paper, results of studies using supercritical carbon dioxide to remove the base oil from drilling waste are presented. Current work investigates the extraction of hydrocarbons (i.e. base oil) from a synthetic oil-based centrifuge underflow drilling waste. Extraction efficiencies as high as 98% have been observed. Additionally, results of both past and current studies indicate that the hydrocarbons are unchanged by the extraction process and that they may be recovered and potentially reused. Introduction In rotary drilling, drilling fluids are essential to lubricate the drill bit and circulate the drill cuttings to the surface. It is well documented that oil-based drilling muds (OBMs, sometimes referred to as non-aqueous drilling fluids or NADFs) have several advantages over their water-based counterparts(1, 2). OBMs have a higher natural lubricity, making them suitable for challenging drilling operations. Also, OBMs are less reactive with clays and shales, thereby preventing hole enlargement, resulting in smaller overall waste volumes. However, OBMs must be carefully handled and treated prior to disposal due to their potential negative environmental effects. There are a number of options available to treat and dispose of OBM drilling wastes (for example, land spreading and landfilling), however the cost of handling and disposing of drilling waste is increasing. The drilling industry is now turning to novel approaches for the treatment and disposal of drilling wastes in order to meet more stringent environmental guidelines(3). Supercritical fluid extraction (SFE) is an extraction technique that uses substances at or above their critical pressure and temperature as solvents. In the vicinity of the critical point, the liquid and vapour phases of the substance merge, producing a fluid with gas-like diffusivity and viscosity and liquid-like density(4, 5). These properties provide for favourable mass transfer of soluble waste components (i.e. hydrocarbons) from solid matrices to the bulk supercritical fluid. The density of the fluid is defined by the pressure and temperature; small changes in processing conditions can fine-tune the solvating power of the fluid(6). Additionally, supercritical fluids have zero surface tension, thereby allowing easy penetration into most matrices(4). Several studies have documented the treatment of OBM drilling waste using SFE. In 1984, a patent by Eppig et al. detailed a system suitable for the removal of organic contaminants from inorganic matrices(7). This patent specifically lists the treatment of oil contaminated drill cuttings as an application of the technology, and indicates that propane, Freon and carbon dioxide would be suitable supercritical fluids for this purpose. A later study by Eldridge investigated the use of a pilot-scale SFE system to treat oil contaminated drill cuttings from North Sea drilling platforms(8).

Summary Nonaqueous drilling fluids are essential in challenging drill operations. Their use, however, requires special treatment and disposal because of their potential for environmental damage. In light of increasing costs for common treatment technologies and ever-tightening environmental legislation, alternative treatment technologies are being sought by the drilling industry. Supercritical fluid extraction is one such technology that employs a substance higher than its critical pressure and temperature as a solvent. In this paper, the results are presented of a study using supercritical carbon dioxide to treat synthetic based drilling waste. Unlike typical supercritical fluid extraction studies in which the process is optimized using changes in pressure and temperature, this study was undertaken to improve the extraction of hydrocarbons from drilling waste by increasing the supercritical fluid solvent to waste ratio. Efforts focused on improving supercritical fluid/drilling waste contact, eliminating system clogging with waste solids and minimizing solids carryover. Alterations to the waste using additives and alterations to the vessel both led to an increased amount of waste being treated effectively using the same amount of solvent. Optimization of the process yielded efficiencies as high as 97%. Also, it has been determined that the extracted hydrocarbons are unchanged by the supercritical fluid extraction process. This result suggests that the collected hydrocarbons may be reused in the drilling process, resulting in significant cost savings to the industry. Introduction In rotary drilling for oil and gas, drilling fluids are essential to clean the wellbore and to lubricate the drill bit. Nonaqueous-based drilling fluids (NADFs) are thought to be superior over water-based drilling fluids because of their higher natural lubricity and lower reactivity with clays and shales [Canadian Association of Petroleum Producers (CAPP) 2001; Melton et al. 2004]. As such, they are often necessary for challenging drill operations. However, they are much more expensive and, because of their hydrocarbon content, the wastes they generate must be handled and disposed of carefully. Numerous techniques have been developed to treat the wastes generated from drilling with NADFs. These techniques include bioremediation technologies, such as landfarming and cleaning technologies (e.g., incineration or solvent washing) (Saintpere and Morillon-Jeanmaire 2000). As environmental legislation becomes increasingly more stringent and the cost of common treatment techniques increases, the drilling industry seeks out new approaches to the treatment of NADF drilling waste (Minton and McGlaughlin 2003).

fax 01-972-952-9435. AbstractNon-aqueous drilling fluids are essential in challenging drill operations. Their use, however, requires special treatment and disposal because of their potential for environmental damage. In light of increasing costs for common treatment technologies and ever tightening environmental legislation, alternative treatment technologies are being sought by the drilling industry. Supercritical fluid extraction is one such technology which employs a substance above its critical pressure and temperature as a solvent.In this paper, the results of a study using supercritical carbon dioxide to treat synthetic based drilling waste are presented. Unlike typical supercritical fluid extraction studies where the process is optimized using changes in pressure and temperature, this study was undertaken to improve the extraction of hydrocarbons from drilling waste by increasing the supercritical fluid solvent to waste ratio. Efforts focused on improving supercritical fluid/drilling waste contact, eliminating system clogging with waste solids and minimizing solids carryover. Alterations to the waste using additives and alterations to the vessel both led to an increased amount of waste being treated effectively using the same amount of solvent. Optimization of the process has yielded efficiencies as high as 97%. Also, it has been determined that the extracted hydrocarbons are unchanged by the supercritical fluid extraction process. This result suggests that the collected hydrocarbons may be reused in the drilling process, resulting in significant cost savings to the industry.

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