Extraction Of Insoluble Organic Matters And Technology Of Oil Removal From Oil-based Drill Cuttings

With the application of oil-based drilling fluids,large amounts of oil-based drill cuttings are produced in the drilling process.This kind of oily waste will cause serious harm to human living and natural environment,and it is urgent to treat it effectively.Under the background of carbon peak and neutrality targets,the discharge standards of oil-based drill cuttings are increasingly stringent.Considering the economic and environmental benefits,it is extremely important to realize the recycling and harmless treatment of oil-based drill cuttings.Although the current disposal methods can obtain better oil removal effect,there are still some problems,such as the solvent extraction method consumes lots of solvent,the pyrolysis method requires excessively high temperature.Based on the principle of "similarity and intermiscibility",the solvent extraction focuses on the oil phase extraction of oil-based drill cuttings,but does not effectively pay attention to the separation of insoluble organic matters.In the solid-to-liquid separation stage after extraction,insoluble organic matters could not be separated from the particles due to high centrifugal speed or long settling time,which affects the oil removal of oil-based drill cuttings.In order to solve above technical problems,the extraction of insoluble organic matters and technology of oil removal from oil-based drill cuttings were studied.Insoluble organic matters were colloidal mixture formed by combining drilling fluids additives with oil and water.The characteristics of each component of oil-based drill cuttings were analyzed,and it was clear that the existence of insoluble organic matters were the main reason causing the difficult to dispose of oil-based drill cuttings.Adding solvent to oil-based drill cuttings can reduce the viscosity of the system.With the help of different components of the density and particle size difference,the insoluble organic matters were extracted into the liquid phase and the cuttings were further treated.After separating insoluble organic matters,the cuttings were similar to the mixture of clean particles and oil phase,which reduced the difficulty of disposing.Oil removal and standard particle discharge could be achieved by centrifugation with water or thermal desorption at low temperature.In this study,solvent extraction of insoluble organic matters could greatly reduce the difficulty of oil removal from oil-based drill cuttings.Removing oil by centrifugation with water was safe and environmentally friendly,which can simply realize the separation of oil,water and solid phase.Low temperature thermal desorption had good oil removal effect,low energy consumption and did not change the properties of mineral particles.The contents of this dissertation are as follows:(1)The basic composition and properties of oil-based drill cuttings were measured.Thermogravimetric analysis showed that insoluble organic matters bound to large amounts of oil phases and restricted their separation,adhered to the surface of particles or voids and blocked the access of oil phases in and out of the hole,resulting in high residual oil content and difficulty in oil removal.Mineral oil was selected as the solvent to separate the insoluble organic matters from oil-based drill cuttings.The extraction parameters were optimized:the ratio of solid to liquid was 1:1,the mixing conditions were 500 rpm,20 min,treated once at room temperature and washed by kerosene.In the oil-based drill cuttings after separating insoluble organic matters,the cuttings particles were weakly bound to the oil phase,and the residual oil content could be reduced to 0.35%～0.92%by centrifugation with water,lower than 1%of the discharge standard.With the help of low-field nuclear magnetic resonance,it was explained that centrifugation with water promoted particle coalescence,free oil aggregation,and oil phase on particle surface was displaced by water phase,finally realizing three-phase separation.By comparing the rheological properties of oil-based drilling fluids prepared with mineral oil or recycled oil,the feasibility of this method for oil phase reuse was illustrated.(2)The thermogravimetric analysis showed that the decomposition temperature of insoluble organic matters was too high because of the composition of fluid loss additive with good thermal stability,which could not be removed by low temperature heat treatment,resulting in higher residual oil content of oil-based drill cuttings.The solvent was converted from mineral oil to organic solvent with low boiling point.The most suitable cyclohexane was selected from the solvent to separate insoluble organic matters from oil-based drill cuttings,which can reduce the temperature and energy consumption of thermal desorption.After separating insoluble organic matters,small amounts of residual cyclohexane and oil phase could be desorbed from the cuttings surface and pores by thermal desorption at 250℃,and the residual oil content could be reduced to 0.14%～0.26%,lower than 1%of the discharge standard.Cyclohexane was separated by reduced pressure rotary evaporation,and the particle oil residual content was always lower than 0.3%after 5 cycles of cyclohexane reusing.Considering the actual process conditions and choosing mineral oil as solvent,the field pilot test was carried out,which further showed that the extraction of insoluble organic matters was the key to oil removal of oil-based drill cuttings.