| Due to the rising demand for oil and natural gas and the limited domestic oil and gas production,China's problem of energy shortage is increasing.The dependence on foreign trade is expected to exceed 70% in 2018.In order to tap domestic resources and increase output,the main battlefield of oil and gas exploration and development has shifted to low permeable,deep layer,ocean and unconventional oil and gas reservoirs with high requirements for drilling technology.Therefore,modern drilling technology,such as horizontal well,complex structural well,deep well,ultra deep well and large displacement well,is widely used in oil and gas exploration and development.Measurement while drilling is an important and indispensable means to realize the above drilling technology,which plays an important role in improving the success of oil and gas exploration,the rate of oil and gas drilling catching,the rate of oil and gas recovery,and thus enhancing drilling efficiency and reducing drilling cost.In order to meet the needs of production field,the number of downhole sensors in MWD is increasing,and accordingly the amount of measurement data is rising.It has become a technical bottleneck to transmit large amounts of these data to the ground in real time,which seriously restricts the application and development of MWD technology.Transmission mode of high speed MWD is the foundation of modern drilling technology.Considering the economy,stability,reliability,transmission speed and depth of uploading,continuous wave transmission is regarded as the best high-speed transmission mode.At present,with the continuous growth of new demand for oil and gas exploration and development,foreign drilling technology is being further deepened and refined,and constantly spawned new technologies that develop rapidly and fiercely,which shows that the system is developing towards high speed,high precision,modularization,high temperature resistance and high pressure resistance.In addition,transmission rate of the commercial application of MWD transmission technology is higher than 10 bps,and the compression rate is over 100 bps.However,continuous wave transmission technology is still a blank,and commercial application of MWD transmission technology is limited to low-end products in China,so there is a big gap compared with the foreign advanced technology.It is of great significance to develop the continuous wave high-speed transmission technology and products domestically and independently for improving the core competitiveness of MWD and developing the oil and gas resources efficiently.Continuous wave generator is the key technology of continuous wave transmission system with its main body as driving components with high dynamic characteristics.The research of high pressure amplitude rotary valve is completed with its focus on the key technology and stability of the principle prototype of the continuous wave generator designed by the author in the paper.Then,based on the finite element analysis model,the rule of the maximum torque output of the high temperature and high pressure cylinder type magnetic coupling is obtained,and the high-temperature and high-pressure cylinder type magnetic coupler with high torque/volume ratio is developed.In addition,the point of view that TC bearing is a kind of dynamic pressure sliding bearing is proposed and then verified.The mechanical characteristics of TC bearing are studied from the perspective of the structural factors combined with the finite element.Based on the study of those characteristics,the application scheme of sand bearing type TC bearing for downhole light load,high speed and sand removal is put forward.Lastly,a mechanical model of upper rotor system consisting of rotary valve rotor,magnetic coupling outer magnetic rotor and TC bearing is established and its stability is studied.Thus,it provides an important theoretical support for our country to develop the downhole prototype of high-speed rate transmission drilling fluid continuous wave generator.The main research results and conclusions are as follows:(1)Based on the theory of pipeline series-parallel connection and the requirement of minimum flow for downhole power drilling tools,a pressure wave with larger amplitude is obtained,which greatly improves transmission speed and information upload depth.Aiming at the fact that the current pressure wave amplitude of drilling fluid continuous wave transmission system is low and the high frequency pressure wave attenuates rapidly in the transmission channel of drilling fluid,which restricts the transmission speed and information upload depth of continuous wave tool while drilling,a high pressure amplitude rotary valve is studied and developed.Based on study of the generation process of continuous pressure waves,and the theory of pipeline series-parallel connection of fluid mechanics,a high-pressure amplitude type rotary valve is studied combined with the requirements of minimum flow for downhole power drilling tools.By the theory of flow characteristics of thin-walled holes,it is verified that the value of the pressure wave amplitude can approach infinity when the axial gap between the stator and the rotor of the rotary valve close to zero.(2)Based on equivalent magnetic circuit method and finite element analysis,the maximum output torque of high temperature and high pressure cylindrical magnetic coupling is obtained.In order to solve the short service life of rubber parts in high temperature and high pressure environment in rotary dynamic seal,the high-temperature and high-pressure cylindrical magnetic coupling is mainly studied.Firstly,analyzing structure and characteristics of magnetic coupling,the structure of the cylindrical magnetic coupling is preferred.Then,based on the equivalent magnetic circuit method magnetic circuit and the principle of the transfer motion are studied for the high temperature and high pressure cylindrical magnetic coupling.The relationship between the coupling magnetic field strength and the maximum transfer torque is established by empirical formula method,and the factors that affect the torque are found out.Next,the characteristics of the high temperature and high pressure isolation sleeve are studied.Finally,in order to understand the distribution of magnetic line of force and the law of torque change intuitively,the numerical simulation of static magnetic field of permanent magnet coupling is further carried out by using Ansoft Maxwell finite element software.Based on a two-dimensional finite element analysis model of 6 magnetic pole cylindrical magnetic coupling for 171 mm drill collar,the magnetic force line path is obtained,which proves the correctness of the analysis of the main magnetic circuit and the leakage magnetic circuit by the equivalent magnetic circuit method,and it is pointed out that the number of distortion of magnetic force line is the most and the torque reaches the maximum value when the turning angle is equal to 30 degrees.Parameters affecting output torque are simulated,and the ways to get larger torque are as follows: 1)Increasing the magnetic induction intensity;2)Increasing magnetic flux density by aggregated magnetic field.(3)It is demonstrated that the TC bearing belongs to the dynamic pressure sliding bearing.The static Reynolds equation of TC bearing is established,and the static characteristic of TC bearing film is studied from the aspect of structure factor.TC bearing is a special compound sliding bearing for oil drilling industry,with drilling fluid as lubricating and cooling medium,so the research on TC bearing at home and abroad is mainly focused on the improvement of manufacturing technology and material.However,TC bearing is studied from two structure factors of eccentricity and width to diameter ratio in this paper.First of all,from the three factors of liquid membrane dynamic pressure,it is verified that TC bearing is a sliding bearing with no special lubrication system.By analyzing the formation of dynamic pressure of TC bearing film and the process of continuous liquid film formation,the correctness of this view is verified again.Next,the static Reynolds equation of TC bearing is established,and we find the relationship between dimensionless dynamic pressure of liquid film and structural factors through the normalization formula of Reynolds equation.By establishing the finite difference model of the TC bearing liquid film,the non dimensional dynamic pressure field of the TC bearing liquid film is obtained,and effect of eccentricity and width diameter ratio on dynamic pressure field of liquid film are discussed,which verify the correctness of engineering method of the infinitely long bearing and infinitely short bearing.The static dimensionless carrying capacity and frictional resistance of liquid film are calculated by corresponding integral,which shows that the dimensionless capacity of liquid film increases with the increase of width diameter ratio and eccentricity,and dimensionless friction resistance are as follows: When the eccentricity is less than 0.6 and the ratio of the width to diameter is less than 1,the frictional resistance of the "shear flow" is dominant;When the eccentricity is greater than 0.7 and the ratio of the width to diameter is greater than 1,the friction resistance of the "pressure flow" is dominant.(4)Based on the theory of dynamic pressure sliding,the mechanical model of TC bearing is established,and the application plan of TC bearing with high speed and light load and chip removal is put forward.The dynamic Reynolds equation of TC bearing and the mechanical model of TC bearing after linearization are established.And 8 dynamic characteristic coefficients are put forward.The normalized Reynolds equation has four "disturbance pressures" for partial derivation of corresponding variables.The influence of eccentricity and width diameter ratio on eight dimensionless dynamic coefficients is analyzed by finite element method.The results show that the orthogonal stiffness coefficient and the orthogonal damping coefficient along the eccentric direction are most sensitive to the change of eccentricity and width to diameter ratio while the cross stiffness coefficient and the cross damping coefficient perpendicular to the eccentric direction are the most insensitive to the change of eccentricity and width to diameter ratio.Due to the small radial clearance between the isolation sleeve and the outer seal layer,the operation of the external magnetic rotor is influenced by the solid particle plug in the gap between the isolation sleeve and the outer seal layer,and thus the existing full circular TC bearing has been improved and the sand guided TC bearing,which is easy to drain,is put forward and then the expression of the thickness of the liquid film of the sand guided TC bearing is given.Because of the discontinuous liquid film,special treatment is needed to discrete liquid film,and the local integral method is applied to solve the dimensionless liquid membrane dynamic pressure,static characteristic,disturbance pressure and eight dynamic characteristic coefficients of sand guiding TC bearing.In addition,the effects of groove parameters on the dynamic pressure of liquid film,the bearing capacity of liquid film and the eight dynamic characteristic coefficients are discussed,and the results are as follows: the groove increases the convergence angle of the liquid membrane;the dimensionless dynamic pressure and the bearing capacity of the liquid membrane are reduced by the number of grooves and the depth of the groove,which have little effect on the eight dimensionless dynamic coefficients.(5)It is verified that the sand guiding TC bearing has high stability.A mechanical model of the upper rotor system is established,and the instability law of the upper rotor system is obtained.Aiming at the fact that interference force for TC bearing liquid film instability is strong in the underground environment and the liquid film of TC bearing is very easy to destabilize under light load condition,which limit the performance of high speed operation of a drilling fluid continuous wave generator that will affect the increase of the transmission rate and cause the problem of the loss of stability of the upper rotor system,the stability study of upper rotor system on continuous wave generator is studied.Then,the factors causing the instability of TC bearing liquid film,the mechanics mechanism,instability of TC bearing liquid film under different working conditions and characteristics of liquid film whirling are analyzed.Two conclusions are drawn by analyzing the effect of eight dynamic characteristics of liquid film on the instability of liquid film from the principle of making work of liquid film force: The cross stiffness of TC bearing is one of the main reasons for the instability of the rotor system;It is proved that the stability of the sand guiding TC bearing liquid is greater than the stability of the full round TC bearing.The mechanical model of upper rotor system consisting of rotary valve rotor,magnetic coupling outer magnetic rotor and TC bearing is established.Moreover,the method of stability of the rotor system,in which multi mass are asymmetrical distribution with supporting bearings,is studied,and the effect of the instability of the upper rotor system is obtained.The results and conclusions obtained in this paper have strong universality,which can provide a theoretical basis for similar applications in drilling. |
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