Experimental Study On Treatment Of Oil Based Drilling Mud Wastes With Supercritical Carbon Dioxide

The waste OBM is a kind of emulsion substance consisting of oil,water,pitch organic particles,drilling cuttings,high-molecular compound and some other impurities.The hydrocarbons,heavy metals and organic matters involved in the waste OBM are heavily harmful to soil,underground water and so on,which is strictly banned to be directly discharged by environmental legislation all over the world.Supercritical carbon dioxide extraction is a highly potential technology to dispose waste OBM,being environmentally friendly,economical efficient and widely available.Supercritical Carbon dioxide?SCCO₂?enjoys many advantages such as nontoxicity,non-inflammability and easy separation.Besides,SCCO₂ has excellent performances in flow,permeation and mass-transfer and is consequently a common solvent for supercritical fluid extraction?SFE?.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.Firstly,SCE experiments are then conducted to extract hydrocarbons from the mud to evaluate efficiencies of various SCE operation parameters including extraction pressure?10-30MPa?,temperature?30-70°C?,extraction duration?0-120min?,CO₂ flow rate?0.02-0.4cm³/s?and string speed?0-500rpm?.The results demonstrate that extraction efficiency could be up to 98%.In addition,gas chromatography is performed,finding that SCE can discharge all hydrocarbon components from C₁₀ to C₂₆,with lighter carbon components of C₁₀ to C₁₄ and n-alkanes?NC?structure hydrocarbons being more easily to be removed under experimental condition.Moreover,the properties of retrieved hydrocarbons have not been altered in extraction processes and can be recycled in drilling processes.Moreover,the response surface methodology is used for the optimization of supercritical carbon dioxide for the extraction of hydrocarbons from the waste OBM.The effect on extraction efficiency of different parameters such as pressure,temperature and duration are evaluated through a Box-Behnken design.Moreover,the mass transfer of a mathematical model developed from the differential mass balance is evaluated with the objective of simulating the extraction process.