Dynamic Performance Simulation Of Pneumatic Impact DTH Hammer

Compared with the traditional mud drilling technology,the gas underbalanced drilling technology adopts the high-pressure compressed air as the drilling circulation medium to carry the rock from the bottom hole to the ground,which can improve the rate of penetration,reduce or even avoid the medium loss,enhance the service life of the drill bit and protect the oil and gas reservoirs,etc.It has been widely applied in recent years.The drilling technology of pneumatic DTH hammer belongs to the gas underbalanced fields.The force generated by the compressed air acting on the hammer and causes it to move reciprocating.And the exhaust gas from the DTH will get into the bottom hole and carry the rock to the ground to finish the full circulation.The drilling technology of pneumatic DTH hammer has the characteristics of high drilling efficiency and long service life of bit,in addition,it has a low requirement for the weight on bit.Combined with the circumferential torque provided by the drilling rig,the rock of the bottom hole broken under the impact load and the rotary chip load.In the drilling projects of hard strata such as deep wells,ultra-deep wells and complex geological conditions(include the desert,remote and water shortage conditions),DTH hammer shows outstanding performance and has been widely used in solid resource exploration,hydrological and geothermal well drilling,oil and gas drilling,etc.A full-hole reverse circulation pneumatic DTH hammer was developed in this paper.The study is mainly focused on four aspects shown as below.(1)The overall design of full-hole reverse circulation pneumatic DTH hammer.Comparing the structure,design characteristics and working performance of the current DTH hammer at home and abroad,proposed a new king of DTH hammer in this paper.(2)Simulation of the impact and collision characteristics between DTH hammer and the drill bit.Established a simulation model of the motion assembly based on the DTH hammer proposed in this paper to explore the ultimate impact velocity and the relationship between the rebound velocity and the impact velocity.(3)Establishing the mathematical model of hammer motion under the compressed air.According to the theory of state changes of compressed air and the structure of DTH hammer,analyzing the move process of the hammer and trying to establish its mathematical model.(4)Numerical calculation of hammer motion and the output dynamic performance analysis of the DTH hammer.According to the mathematical model,trying to adopt the method of programming to obtain the movement characteristic curves of hammer under different inlet pressure,and based on which to analyze the output dynamic characteristics of DTH hammer.The main results and conclusions are as follows:(1)Proposed a new king of DTH hammer in this paper named full-hole reverse circulation pneumatic DTH hammer,and completed the overall design of it.This paper reviewed the development history of gas underbalanced drilling technology and DTH hammer drilling technology,and summarized the application advantages and development trends of pneumatic DTH hammer drilling technology in oil and gas industry.Based on the literature and product information summarized in this paper,the author drew the conclusion that DTH hammer will gradually develop towards medium and high pressure,valveless and reverse circulation drilling technology.Combining with the structure,principle,advantages and disadvantages of several reverse circulation DTH hammers developed by lots of research institutes and large international companies at home and abroad,the overall design of a kind of full-hole reverse circulation pneumatic DTH hammer was completed and its five design features were introduced respectively.(2)Simulation of the impact and collision characteristics between DTH hammer and the drill bit was completed.According to the overall structure of the DTH hammer,the author established a simulation model about the impact and collision components between DTH hammer and the drill bit.Based on the simulation model,the author used the Automatic Dynamic Analysis of Mechanical Systems(ADAMS software)and the Explicit Dynamics System of ANSYS Workbench to simulate the impact and collision characteristics.Finally,the relationship between the rebound velocity and the impact velocity was obtained asV_h=-0.302V_m+0.658.And according to the material properties of DTH hammer,the ultimate impact velocity should not exceed 7.2 m/s.(3)The mathematical model of hammer motion under the compressed air was established.Based on the DTH hammer,according to the gas distribution status of the upper and lower chambers of the cylinder at different positions of the hammer,the movement process of upper stroke and lower stroke was divided into three stages respectively.And according to the theory of compressed air(such as the ideal gas equation,adiabatic process of air etc.)and the differential equation of the hammer in quasi-static process,the mathematical model of the hammer motion was established.(4)The movement characteristic curves of hammer under different inlet pressure were obtained by the method of programming,and based on which the author analyzed the output dynamic performance of DTH hammer.On account of the mathematical model established in the previous chapter and the rebound of the hammer after impacting the drill bit,adopting the MATLAB software,taking the output characteristic of the hammer as the final calculation result while the motion process reached a steady state,the kinematic characteristic curve and corresponding dynamic performance parameters of DTH hammer were obtained finally.Through the analysis of the characteristic parameters under the different inlet pressure,such as the impact stroke,energy,frequency and so on,and combined with the conclusion of Chapter 3,it is concluded that the range of working pressure is 0.8-1.3 MPa,and the frequency is about 8.9-13.2 Hz,the thermal efficiency is about 43.6%-61.1%.