Experimental study on harmless disposal of waste oil based mud using supercritical carbon dioxide extraction

摘要

Oil based mud (OBM) is widely used in unconventional oil and gas drilling industry due to its advantages of harmlessness to reservoir and inhibition of shale swelling. However, hazardous and poisonous contaminants in the mud could not be discharged with conventional disposals and treatments, which are of low economic efficiency and negative environmental. Therefore, alternative treatment technologies such as supercritical carbon dioxide extraction (SCE) are being of more and more concern in drilling operations. In this paper, X-ray fluorescence (XRF) and Ultraviolet-visible spectrophotometry (UV-VIS) are applied to examine the contents of different contaminants in the oil based mud from the North China Sea, which indicates that the hydrocarbon concentrations significantly exceed the normal value while the heavy metals are negligible. SCE experiments are then conducted to extract hydrocarbons from the mud to evaluate effects of various SCE operation parameters including extraction pressure (10-30 MPa), temperature (20-65 degrees C), extraction time (20-150 min) and the mass ratio of supercritical carbon dioxide to waste OBM (1-12). The results demonstrate that extraction efficiency could be up to 98% under the temperature of 35 degrees C, the pressure of 20 MPa and the extraction time of 60 min. In addition, gas chromatography is performed, finding that SCE can discharge all hydrocarbon components from C-10 to C-26, with lighter carbon components of C-10 to C-14 and n-alkanes (NC) structure hydrocarbons have more removability under experimental condition. Moreover, the properties of retrieved hydrocarbons are not altered in extraction processes and can be recycled in drilling processes.