Oil-based cuttings (OBCs) produced by shale gas exploitation are classified as hazardous waste. Their appropriate utilization and disposal is a key issue that urgently needs to be resolved. A single-phase microemulsion (SPM) has ultra-low interfacial tension and strong solubilization ability. In view of this, based on an analysis of the characteristics of OBCs, SPMs have been selected for their cleaning. The effects of microemulsion components and other conditions on the cleaning efficacy have been explored, as well as the deoiling mechanism and the recycling efficiency of the SPM. Our results have shown that sodium dodecylbenzene sulfonate (SDBS), n-butanol, water, and white oil in appropriate proportions can form an effective SPM. The oil content (OC) of OBCs after cleaning was reduced from 11.89% (±0.32%) to 1.13% (±0.02%) when the proportions of the aforementioned components of the SPM were 14.3%, 14.3%, 66.6%, and 4.8%, respectively. The OC of the residue further decreased to 0.28% (±0.05%) after a second cleaning with an alkaline solution. The optimum SPM conditions for cleaning OBCs were identified as a stirring speed of 200 rpm, a temperature of 30 °C, a cleaning time of 30 min, and a solid to liquid mass to volume ratio of 1:4. The main mechanism whereby the SPM cleans the OBCs is that the former reduces the combined work and adhesion work required for the removal of oil droplets from the cuttings, so that the adhesive oil is easily gathered up. Furthermore, the gathered oil phase is solubilized by the SPM.
Keywords: Oil-based cuttings; influencing factors; mechanism; microemulsion; shale gas.