Study On Pollution Characteristics And Pressurized Hot Water Extraction Of Shale Gas Oil-based Drill Cuttings

Oil-based drill cuttings?OBDC?is a kind of organic solid waste produced in oil and gas exploitation.It has been listed in List of National Hazardous Wastes?HW08?in China.Shale gas is emerging fossil energy in recent years.Due to the special geological structure of its gas storage formation,large amounts of OBDC are inevitably generated during the drilling process of its exploration and exploitation.Shale gas development vigorously develop in Chongqing,the main battlefield of China's shale gas.At the same time,the environmental problems caused have gradually been taken seriously.Among them OBDC ranks first.Chongqing shale gas wells are mostly in remote forests and OBDC produced in the past were not of public concern.However,in recent years after the introduction of relevant environmental regulations,the treatment are temporary reference to ordinary oil sludge and difficult to meet the processing requirements.In this paper,the properties and composition of shale gas OBDC were analyzed to evaluate the pollution characteristics.Then,based on the properties of oil-based cuttings,pressurized hot water extraction?PHWE?treatment of shale gas-based cuttings was proposed.The effects of various parameters on the treatment of oil-based drilling were studied in a batch reactor.Finally,based on the experimental results of the first two parts,the steam immersion of oil-based cuttings was studied in a continuous reactor,which provided the basis for the pilot-scale amplification.The main research contents and results are as follows:Firstly,the analyses of two OBDC samples selected from the horizontal well and vertical well in Chongqing show:?1?The main content of two samples are ash and oil-based organic matter,but the oil and ash content is in a certain difference.?2?Thermogravimetric Analysis showed that the evaporation of water and oil was mainly occurred at 100-300?.The pyrolysis or oxidation of non-oil organic matter occurred at300-550?.?3?The main organic compounds in OBDC are alkanes,olefins and polycyclic aromatic hydrocarbons,but the proportion is different in two samples.?4?The main components of ash are CaCO₃ and BaSO₄,SiO₂ and Fe₂O₃.The content of As,Cd,Hg and Zn in the two oil-based cuttings exceeded the Soil Standard in China.?5?Organic matter,heavy metals,alkaline salts are harmful substances in OBDC.Secondly,in the intermittent PHWE experimental part,the operation was carried out at different temperatures,water volume and dip times,and the effect of each parameter on the effect was studied,the results were also compared with the oxidation-immersion combined method and the thermal desorption.The experimental results show that:?1?steam immersion has a similar oil recovery compared to thermal desorption,but the treatment is better.?2?The efficiency of intermittent PHWE is most affected by temperature.The increase of the times of dipping can improve the treatment effect,but the effect weakened after more than 4 times.The phase of water at the same temperature has little effect on the immersion effect.?3?Addition of the oxidant can greatly reduce the oil content of the product,but the oil recovery is reduced and the volume of the gas produced is significantly increased.Finally,a continuous PHWE study was carried out in a process and scale closer to the industrial application.The effects of temperature,flow rate and pressure on the rate and results of steam immersion were investigated.The experimental results show that:?1?Temperature,flow,pressure can affect the rate of steam immersion,but the role of different sizes.?2?By this method,the residual oil content of the two oil-based cuttings samples can be 0.63%and 0.15%,respectively.In this process,contaminants were transferred from hazardous waste at higher cost of treatment to easily treated water and the recovery of oil is achieved.In addition,it discharges little harmful gas.As a result,it is a promising OBDC disposal method.