Theory And Technology Research On Coal Particle Cleanouts Of Deliquification Process And Jet Vacuuming In Coalbed Methane Wellbore

The coal particle cleanouts technology is regarded as the key technology of making continuous and steady production in coalbed methane(CBM) wells. Based on the results of investigation in production field of Ordos basin, the coal particle migration and carrying out were analyzed. Then the solid-liquid two phase unsteady flow was solved by dynamic meshing methods based on unstructured grid, pressure balance coal particle cleanouts process was designed, the jet vacuuming cleanouts system was optimized, and the coal particles cleanout apparatus was tested. The research is valuable in theory and application, as it contributes to deliquification process parameters design and solving gas channel failure caused by the CBM well killing or blowout.On the basis of rock mechanics, coal particle is produced by shear, compaction and sliding coal seam failure. The mechanical model of a single spherical coal particle settling was built to obtain it’s the settling character. The group coal particle settling velocity was obtained by introducing the volume concentration. The single random coal particle settling character experiment was conducted to obtain the shape coefficient; the single random coal particle moving character in flow liquid experiment was also conducted, in which the linear relationship between the coal particle velocity and the water velocity was found. Based on the single phase flow friction loss, using the solid-liquid two phase mixture as homogeneous medium model and the theory of diffusion, the pipe friction loss of coal particle water two phase flow was calculated.The annulus between rod and tube in sucker rod pumping well has a moving boundary due to the rod’s periodic motion, which makes the two-phase flow of coal particle and water a complicated transient problem. This research adopts dynamic meshing theory to handle the grid node’s movement both on the boundary and in the flow field. The method gives grid high quality as an initial condition to precisely solve the unsteady flow field. Mathematical Modeling of solid-liquid two phase flow is solved by simplec methods based on unstructured grid. We acquired the coal particle’s velocity and concentration before the mass flow rate at the inlet and outlet of annulus was gained, and computed the integral for flux in different working conditions. The coal particle emission is influenced by the rod’s periodic motion disturbance, which makes the coal particle clean out differs with different stroke and rate of pump, while the pump output volume is same. This difference increases while the coal particle diameter increases and the pump output volume decreases. The conclusion helps to decide the deliquification process parameters and pumping units.Once solid materials like coal particle settle down in the bottom of CBM wells, it will cause stuck pump and other serious consequences. The normal coal particle cleanouts operation usually causes more coal particle production due to the pressure fluctuation, which destroys the gas channel formation. The reason of gas production reduction was figured out. The quick coal particle cleanouts operation process was put forward as an innovation. When working in order to further implement the protection of coal reservoir and gas channel, the not well killing(pressure balance) jet vacuuming negative pressure coal particle cleanouts operation device was designed, and expounded in detail the operation process and device of coal particle cleanouts working principle and equipment composition.Based on the theory of jet pump and the law of energy conservation, the basic performance equation of the pump was derived by employing Lorenz mixed loss model. The main influence factors of the coal particle cleanouts operation efficiency was analyzed, then the specific performance was researched, combining physical properties and production parameters of CBM wells. According to four constraint condition: the artificial lift minimum pressure ratio, the cavitation maximum flow rate ratio, the optimum area ratio and the coal particle cleanouts minimum flow rate. Optimization design mathematical model was established in order to acquire the optimal structure and process parameters. In addition, the jet vacuuming coal particle cleanouts apparatus was overall designed and intensity checked. In the end, the full size model machine was manufactured for the requirement of field use.In order to determine the reasonable structure and working parameters of coal particle cleanouts apparatus, and realize the optimization design and efficient operation of coal particles cleanout jet system, theory analysis on the working principle of coal particles cleanout and motion process of coal particle was done. The bottom hole coal particles cleanout jet flow field can be divided into six areas: free jeting area, jet impinging area, radial flowing area, reflux area, vortex area and negative pressure suction area, which resulted in the spiral uprising motion state of coal particle. Coal particles cleanout experiments were designed by uniform design method, regression equation was found by quadratic polynomial stepwise regression method, the inter coupling influence relation of nozzle structure parameters, jet parameters and coal particle characters to impinging depth was revealed. The results showed that the arrangement of these parameters was jet distance, nozzle diameter, nozzle flow rate, and coal particle diameter according to their effects on impinging depth. The influence of nozzle flow rate, nozzle diameter and jet distance on impinging depth was obtained in detail by further single factor experiment.