| Radial drilling,as a technology for oil and gas production and stimulation,has been put into use in the field of conventional oil and gas exploitation.The application in the field of coalbed methane is still not mature.The main reason is that the physical properties of coal rock are different from those of conventional oil and gas,Resulting in hydraulic coal breaking mechanism goes in a different way.It is the key to apply the radial well technology in the field of coalbed methane to find out such difference and propose a solution to that problem.Based on the description of high-pressure water jetting,the fluid-solid coupling model of hydraulic coal breaking mechanism is established,the numerical solution of which analyzes the axial and radial velocity and pressure distribution after the jet leaves the nozzle.And also,the statistical damage model of coal rock failure process is established,and the obtained model can fairly reflect the evolution characteristics of coal rock failure process,where parameters ? and ? represent the uniformity level of coal rock intensity in a macroscopic and microscopic way,respectively.Finally,the pressure loss is divided into two catogories,useful pressure loss and useless pressure loss,and influencing factors in radial drilling process are analyzed.Through the calculation of pressure loss during operation,it is found that some mechanical properties such as tensile strength and compressive strength and the length,inner diameter of high pressure hose have the most significant effect on hydraulic coal breaking.On the other hand,the higher surge pressure,the faster the erosion rate,specially at 3 to 8 times the critical breakdown pressure,the erosion rate is about 0.4 times as much as dimensionless surge pressure. |
PDF Full Text Request