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).
Non-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. Introduction In rotary drilling for oil and gas, drilling fluids are essential to clean the well bore and to lubricate the drill bit. Non-aqueous based drilling fluids (NADFs) are thought to be superior over water based drilling fluids due to their higher natural lubricity and lower reactivity with clays and shales1,2. 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 include bioremediation technologies such as landfarming and cleaning technologies such as incineration or solvent washing3. 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 waste4. Supercritical Fluid Extraction. Supercritical fluid extraction (SFE) has recently been investigated as a possible NADF drilling waste treatment method. SFE uses a substance above its critical pressure and critical temperature as a solvent. In the vicinity of the critical point, the gas and liquid phases of a substance will merge, producing a fluid with properties intermediate of both phases5,6. Of particular note are the gas-like diffusivities and viscosities and the liquid-like densities of supercritical fluids. These properties allow for efficient mass transfer of solutes into the bulk supercritical fluid. Additionally, supercritical fluids have a near zero surface tension allowing easy penetration into most matrices5,6. Unlike typical solvents, however, the properties of supercritical fluids may be fine tuned to change their solvating power7. By simply altering the process conditions of pressure and temperature, one can achieve different densities of supercritical fluid and, as a result, alter the extent to which a solute will dissolve in the fluid.
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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