Numerical Simulation And Experimental Study On Gas-Solid Flow Field Of DTH Hammer Reverse Circulation Drilling

The mineral resources are the material basis of the progress of human society andeconomic development. With the rapid economic development, the demand for resources ofthe human society is increasing, but the reserve of the mineral resources is less and less.After years of development and utilization, the exposed mine, the shallow ore and the easyto identify mineral have already been explorated away, so the mineral exploration graduallychange to find the concealed ore, the deep mine, the difficult identified mine. With thedifficulty and cost of exploration increasing, the traditional drilling technology methods cannot meet the needs of the current mineral exploration.Hollow-through DTH hammer reverse circulation continuous coring technology is anadvanced drilling technology, which sets DTH hammer impact and rotary broken rock,circulating medium full-hole reverse circulation and synchronization acquisition rock coresduring drilling three processes in one. After years of development, the technology has beenused in practical applications, but it is found that when drilling in the fractured and dropoutstratigraphic, there are some problems such as reverse circulation insufficient capacity, lowcore recovery.In this paper, aiming at the problems of hollow-through DTH hammer reversecirculation drilling technology applied in the actual field, the characteristics of the holebottom gas-solid flow field of the ejector reverse circulation bit is studied by thecomputational fluid dynamics software (FLUENT). Based on mechanism for generation ofarticficial tornado, a new type of reverse circulation bit is designed with a name of cyclonebit, and the reverse circulation effect between the ejector bit and the cyclone bit iscontrasted. By numerical simulation and laboratory experiments, the relation between thereverse circulation effect of the cyclone bit and the structure parameters of cyclone nozzleis analyzed. In this paper, main conclusions are as follows: (1)Field tests showed that when used ejector bit drilling in crack stratum, the effect ofreverse circulation is poor, so the cuttings at the hole bottom can not be transported to thesurface, and the core recovery is reduced. The reason of this phenomenon is that a goodejector structure is not be made up by the bit and the rock of drilling hole.(2)The cuttings of the reverse circulation drilling are regular in grain size distribution.From the grain size cumulative curve of the cuttings samples, it is showed that thegradation of cuttings is poor, and the quality of cuttings under2mm is more than the others.Using the Rosin-Rammler function, the cuttings samples is described, and the grain sizedistribution of cuttings is in conformity with R-R distribution.(3)The numerical simulation results of the hole bottom flow field of the ejector bitshow that, with the different bottom hole drilling conditions, the flow field boundaryconditions of the drilling hole is changed, and the parameters of gas fluid chang obviously,such as velocity, pressure, turbulence characteristics. From characteristics of the gas fluid, itis known that with drilling in complete formation conditions, the gas at the hole bottom iscapable of forming a good reverse circulation, and it also has a suction effect on the annulusfluid. With drilling in crack stratum, a portion of the airflow into the formation by fractures,so the air loss is serious. When the bit is lift from the bottom of the hole, the capacity ofentrainment of the bit is reduced.The capacity of carrying cuttings of the ejector bit are closely related to the location ofcuttings entering into the flow field, the particle diameter and the hole bottom conditions.For the injection position of the cutting particles, the bit can carry the cuttings near thecenter of the bottom into the center channel of the bit, but unable to convey the cuttingsaround the circumference of the hole bottom. For the diameter of the cutting particle, theability of carrying cuttings of the ejector bit with descending order is that0.1mm>1mm>5mm. For the different hole bottom condition, the reverse circulation capacity of the ejectorbit in descending order is that complete stratum> crack stratum> the drilling tool lift.(4)The numerical simulation results of the cyclone type reverse circulation bit holebottom flow field show that, with the different bottom hole drilling conditions, the changesof the flow field are focus on the gas flow characteristics in the bottom of the drilling hole. For the changes of the gas flow in the hole bottom, the pumping capacity of the cyclone bitis strong, and less affected by the hole bottom flow field conditions. The mass flow rate ofthe center hole of the cyclone bit is2times more than the amount of injected mass flowrate.The capacity of carrying cuttings of the cyclone type reverse circulation bit keeps in ahigh level, and there is no significant effect on the capacity by the location of the cuttingsentering into the flow field, the particle diameter and the hole bottom flow field conditions.The cyclone bit has strong reverse circulation ability, and the capability of carrying cuttingsin the complete stratum conditions is close to100%, and the portability efficiency ofcarrying cuttings for all of drilling conditions is higher than90%.(5)Contrast the gas-solid flow field characteristics of the ejector type reversecirculation bit and the cyclone type reverse circulation drill bit, the reverse circulationcapacity of the cyclone bit is better than that of the ejector one. The cyclone bit has theadvantages such as well-adapted for different stratum conditions, strong capacity forcarrying cuttings and less mass flow rate for carrying cuttings than ejector bit.(6)The main reverse circulation structure parameters of the cyclone reverse circulationbit include three: the diameter of the cyclone nozzle, the inclination of the cyclone nozzle,the height of the cyclone nozzle. The variation law of the reverse circulation effect of thecyclone bit by the structural parameters of cyclone nozzle is as follows. With the diameterof cyclone nozzle increasing, the mass flow rate of annulus varies as a quadratic parabola,and achieves the maximum value in diameter of5mm. With the angle of cyclone nozzleincreasing, the mass flow rate of annulus monotonically decreasing. The height of cyclonenozzle exercises a smaller influence on the mass flow rate of annulus. There is a slightincrease in the mass flow rate of annulus with the value of the height increasing, and theresi a linear relationship between them.