Experimental investigation of surfactant-enhanced washing and supercritical CO₂: extraction processes for waste drilling mud remediation

Waste drilling mud is the second largest waste stream produced in the oil and gas industry after produced water and cannot be discharged or landfilled without proper treatment to meet regulatory requirements. Various contaminants are present in the waste drilling mud, including petroleum hydrocarbons, heavy metals, BTEX (benzene, toluene, ethyl benzene, and xylenes), polycyclic aromatic hydrocarbons (PAHs), and other hazardous materials typically originating from the base drilling fluids. Strict environmental regulations are in place regarding the disposal of the waste drilling mud and cuttings to minimize their effect to the environment. Therefore, the waste drilling mud must be properly treated before being released into the environment. Different technologies have been proposed for waste drilling mud remediation; however, most of them are unable to meet the strict environmental regulation limits. In this thesis, different technologies to treat the waste drilling mud are reviewed. After a technical comparison, physical treatment technologies were selected as the most suitable methods. The main aim of this study is to investigate the abilities of the methods of surfactant-enhanced washing and supercritical CO₂ extraction, to treat the waste drilling mud and remove the hazardous petroleum hydrocarbons to meet the strict environmental regulations. The specific objectives of the study are to: (1) characterize the waste drilling mud using particle size distribution, X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometer (ICP-OES), scanning electron microscope (SEM), and gas chromatography GC analyses; (2) identify of the most efficient, environmentally-friendly, and cost-effective technologies to treat the waste drilling mud; (3) screen and select the best surfactants for drilling mud remediation using interfacial tension and sorption analyses; (4) experimentally determine the impacts of significant factors on the efficiency of the two physical processes, surfactant-enhanced washing and supercritical CO2 extraction (SCE); (5) optimize both the surfactant-enhanced washing and supercritical CO₂ extraction processes; and (6) evaluate both the physical treatment processes considering efficiency, environmental impacts, and possible separation and/or recovery of hydrocarbons. A technical review was completed by considering key factors in an efficient process for waste drilling mud remediation, including efficiency, particle size effect, environmental impact, cost, energy requirement, and processing time. Surfactant-enhanced washing and supercritical CO₂ extraction were selected as two viable, efficient, and environmentallyfriendly physical treatment methods. Three surfactants, one anionic (Alfoterra 145-8S 90), one non-ionic (Triton 100), and one biosurfactant (Saponin), were experimentally analyzed, and Triton 100 (TX-100) was selected as the best surfactant based on the interfacial tension and sorption analyses. Experiments were conducted to investigate the effect of different parameters on the surfactant-enhanced washing process’ efficiency, using Triton 100 as the most suitable surfactant, including (i) contact time, (ii) surfactant concentration, and (iii) temperature, and to obtain the optimized operating conditions. The supercritical CO₂ extraction experiments were also designed and conducted to investigate the effects of three parameters, including (i) temperature, (ii) pressure, and (iii) contact time on the process’ efficiency. The result of this study suggested that even though the surfactant-enhanced washing was able to remove up to 70% of the petroleum hydrocarbons, the process could not be employed to treat the waste drilling mud to meet the landfilling regulations. The supercritical CO₂ extraction process, however, was capable of removing the petroleum hydrocarbons up to more than 97% when operated at the optimized conditions and could effectively remediate the waste drilling mud considering the initial total petroleum hydrocarbon concentration). Based on the results of this study, supercritical CO₂ extraction (SCE) process was recommended as an efficient and environmentally-friendly method to remove the total petroleum hydrocarbons from the waste drilling mud to meet the provincial, national, and universal environmental regulations. The SCE process could easily separate the hydrocarbons from the waste mud effectively and in a short amount of time. The supercritical CO₂ extraction process could be tested and implemented for other contaminated substances with petroleum hydrocarbons as well. Although further investigation may be required, the results of this study can be a guide for future research on similar remediation processes