| The green resource treatment of oil-containing cuttings is the bottleneck that restrict the environmental development of shale gas.The hammer-milling thermal desorption device is a new type of environmental protection equipment to solve the problem of oil-bearing drill cuttings in shale gas.However,at present,the research on the movement and migration of drill cuttings under hammering,the key mechanisms of processing such as crushing,temperature rise and thermal analysis are not deep enough,resulting in high energy consumption of the technology and slow on-site promotion and application.To this end,this paper uses a combination of field test,discrete element simulation and theoretical analysis to carry out the research on the analytic transport law and treatment characteristics of shale gas drill cuttings,revealing the mechanism of hammer-milling thermal desorption,which provides theoretical support for the development of the device.The main research work and results of this paper are as follows:(1)An oil-based cuttings hammer-milling thermal desorption test station was built on the Weiyuan shale gas development platform.The field test of oil-milled drill cuttings was carried out by the hammer-milling thermal desorption.The treatment process was analyzed and the particle geometry of the drill cuttings was obtained.The results show that the average oil content of the drill cuttings after treatment is 0.48%,which can be regarded as dry solid.After the hammer-milling thermal desorption,the particle size of the drill cuttings is obviously reduced,which indicates that the hammer-milling thermal desorption has obvious crushing effect on the cuttings.Therefore,during the hammer-milling thermal desorption continuous process,the particle size distribution within the mill is the union of the size of the drill cuttings before processing and the size of the cuttings after processing.(2)Comprehensive analysis and determination of particle model,contact model and contact parameters in discrete element simulation.Combined with the characteristics of dense drill cuttings,heavy drilling chip bed,and rapid liquid phase vaporization in the hammer-milling thermal desorption process,it is determined that the soft ball particle model and the Hertz-Mindlin contact model are used in the discrete element simulation.Besides,the orthogonal test scheme of L25(56)was designed by the method of angle of repose calibration,and the contact parameters in the discrete element model were calibrated.(3)The law of drill cuttings migration under the hammer-milling thermal desorption is studied from the aspects of circumferential and radial motion of cuttings,axial migration and its influencing factors.Analysis of the circumferential and radial motion of drill cuttings shows that the cuttings flow has a similar "turbulent" motion,that is,not only the relative sliding between the layers,but also migrations within the fluid layer and mixing between the fluid layers.The circumferential velocity of the cuttings flow is the main velocity component.Under the action of the hammering blades,a "wedge" high circumferential velocity region from the blade to the cylinder wall is formed,which promotes the layer.The cuttings have a large moving distance along the direction of the wall,high speed and good thermal analysis effect,which is beneficial to hammer-milling thermal desorption.The radial velocity is small,indicating that there is turbulence between the particles and is conducive to the uniform treatment of cuttings.Analysis of the axial migration of cuttings shows that under the action of hammer-milling thermal desorption,the cuttings are pressed against each other and continuously reciprocate,so that the migration of-individual drill cuttings is disordered,but the migration of the cuttings flow has directionality,that is,the continuous movement to the discharge port.Analysis of the factors affecting the axial migration of cuttings shows that the treatment process parameters are the main factors affecting the migration of cuttings,especially the adjustment of the relationship between feed and discharge,and it is necessary to pay attention to improve the effect of cuttings migration,which may shorten the processing time and adversely affect the treatment effect.Although the structural parameters of the device are not the main factors affecting the migration of cuttings,reasonable structural parameters of the device will help ensure reasonable processing time and treatment effect.(4)The processing characteristics of the hammer-milling thermal desorption were studied.The drill cutting crushing was qualitatively analyzed according to the force chain structure of the cuttings flow.The drilling heat generation simulation model was established to explore the heat generation characteristics of the cuttings flow.Based on the heat balance,cuttings handling capacity and its influencing factors were analyzed.The results show that the main crushing area of cuttings flow is the contact line between the stock pile and the material layer and either side of it.The increase of the blade rotational speed can effectively promote the crushing of the cuttings.In the frictional heat field of the cuttings flow,the contact area with the inner wall is the strongest,and the heat generation capacity of the core of the material is the weakest.The increase of material bed quality,temperature rise rate and feed temperature can increase the amount of cuttings treatment,while the high water content of the feed will reduce the treatment volume.Among them,the temperature rise rate has the greatest influence on the throughput of drill cuttings,xvhile the bed quality,the water content and the feed temperature are in turn followed.Therefore,the treatment effect can be improved by increasing the blade rotational speed,avoiding the flow reduction of the drill cuttings in the material bed,pretreating the oil-containing cuttings to reduce the water content thereof,and appropriately increasing the quality of the material bed. |
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