Research On Harmless Treatment Technology For The Waste Oil-based Drilling Fluid

With the continuous development of China’s oil and gas exploration, oil-based drilling fluid technology is developing and the output of waste oil-based drilling fluid is also increasing. The waste oil-based drilling fluid contains large amounts of petroleum and heavy metal elements and other substances, which make great influences on environment. Currently, the treatment technology of waste oil-based drilling fluid is not perfect enough, and obviously there are drawbacks and limitations. How to degrade the waste oil-based drilling fluid reasonably becomes the bottleneck that prevents the development of China’s drilling technology.Firstly, this paper summarizes the composition, characteristics, hazards of the oil-based drilling fluid and the inland and overseas resent researches of waste oil-based drilling fluid treatment methods; Secondly, analyses the lixivium of waste oil-based drilling fluid and definites the content of pollution factors such as pH, COD, oils and heavy metal elements. Then analyses the composition of the waste oil-based drilling fluid and composition of sludge which caused by solid-liquid separation, carries out the demulsification experiments of the output liquid, confirm the best conditions of demulsification. Finally, the supercritical water oxidation experiments of solid-liquid separation sludge is done.The experimental results show that: The waste oil-based drilling fluid contains hexavalent chromium, total chromium, copper, zinc, cadmium, beryllium, nickel, lead, although they have been checked out but not to exceed the standard. However the total silver, arsenic, selenium, mercury and other pollutants have not been checked out. For BaSO4 is the main continent of drilling fluid, the content of barium conforms to the standard value. COD and oils reaches up to 198765 mg/L and 34776 mg/L, 1325.1 and 3477.6 times more than the standard, respectively. We can know that the waste oil-based drilling fluid is hazardous waste, it may causes serious harm to the environment if it has not been treated.The best conditions of demulsification experiments: the best demulsifier SP quantity is 40mg/L; the best demulsifier PAC quantity is 800 mg/L; the best demulsifier PAM quantity is 8mg/L; the best reaction time is 60min; the best temperature is 65 ℃; the best centrifuge speed is 3500 r/min; the best centrifuge time is 4 min.Under the best demulsification conditions, oil recovery rate is 90.03%, COD of the waste water coming from chemical demulsification experiments is 4213 mg/L, beyond integrated wastewater discharge standard and it needs to be treated again.The best conditions of supercritical water oxidation experiments: the best reaction temperature is 450 ℃; the best reaction pressure is 26 MPa; the best reaction residence time is 10min; the initial hydrogen peroxide, the ratio of the actual amount and theoretical demand is 4; initial COD is 2600 mg/L; optimum pH value is 10; Under the best experiments conditions, COD removal rate is 97%, oil in sludge is 355 mg/kg, below the standard “GB4284-84”; COD in the waste waster is 68 mg/L, below the integrated wastewater discharge standard.