Analysis On Flow Field Of Closed-Cycle DTH Air Hammer Drilling System With Three Channels

Human demands for energy sources increase with the development of global economy,leading to the decreases of reserves and scales of conventional oil and gas resources as well as the increase of development effort day by day.Meanwhile,with enormous reserves,unconventional resources have the potential to replace the conventional oil and gas resources.However,the technical requirement for exploration and development of unconventional resources increases because of its great development difficulties.The domestic reserve of oil and gas recourses is relatively scanty and many of them locate in the area with complicated geological conditions.In order to solve the difficulties of drilling process encountered and improve the drilling efficiency and save the drilling cost,a new technology of closed-cycle DTH(Down the Hole)pneumatic hammer drilling with three channels put forward innovatively.This drilling technology is mainly characterized by independent circulation of compressed air to drive the pneumatic hammer high impact drilling and the cooperation with circulated drilling mud to push the slag and protect the stability of hole.The matched drilling tool system mainly includes: coaxial drill pipe with threefold walls,closed-cycled pneumatic hammer and the corresponding button bit.The various flow field of the drilling system is proceed was analyzed in this paper by numerical simulation,including the gas flow-field in the coaxial drill pipe with threefold walls and that in the closed-cycled pneumatic hammer,as well as the fluid flow-field of drilling mud in the bit at the bottom of the hole.The main research contents and progress achieved are as follows:1.Analysis on gad flow-field in the coaxial drill pipe with threefold wall was carried out by Flow Simulation software.The partial flow field of joints with different structure and size was analyzed firstly to determine the optimal structure of the joint.The results show that the pressure loss of the drill pipe can be greatly reduced when the guiding lug of the pipe joint extends at a certain distance from the bottom of the joint,and the influence of the structural size of the joint of the drill pipe joint on the pressure drop is relatively small.Then the pressure loss of the whole drill pipe in different conditions of gas supply was simulated to get the law that the pressure changes with the gas pressure and gas flow.The pressure drop of the drill pipe decreases with the increase of the air supply pressure,and increases with the increase of the air supply.2.Analysis on gad flow-field in the closed-cycled pneumatic hammer was carried out.The pressure loss of the pneumatic hammer mainly includes two parts: the energy dissipations of the compressed gas to drive the pneumatic hammer work and the pressure loss that formed in the internal channels.Simulation analysis on the working process of the closed-cycled pneumatic hammer was carried out by AMESim software to research the performance under the different condition of gas supply.It show that the working performance of the pneumatic hammer increases with the increase of air supply pressure,but the flow rate of compressed air increases accordingly,which means that the requirement of air compressor is improved.Analysis on the pressure loss in different gas pressure was carried out by Flow Simulation software simultaneously.The results can provide a credible basis for the parameter settings of the air compressor during drilling process.When the air supply pressure rises,the pressure loss in the air passage of the pneumatic hammer fluid passage decreases,and the pressure loss decreases as the air supply pressure rises.3.Simulation analysis on the drilling mud in the drill bit by Fluent software to research the flow field down the hole when the nozzles on the drill bit in different diameters and different angles.The analysis results indicated that the smaller the nozzle diameter of the drilling bit is,the more conducive to the hole cleaning and auxiliary rock breaking,but the mud pump is required to improve its power in the meantime.The tilt angle of the bit should not be too large or too small,or it will be harmful to the cleaning and transportation of debris at the bottom of the hole.And the tilt angle should be 15 ° according to the simulation results.It can provide a theoretical foundation for the structural optimization design of drill bit and the selection of working parameters of slush pump during drilling process.