Research On Technology Of Drilling Combined Rotary With Direction And Related Mud Pulse MWD

Gas drainage is major methods not only for gas control but also for methane utilization in coal mine.Directional borehole is effective approach for gas drainage in underground coalmine which have different characteristics such as controllable trajectory,long borehole for gas drainage,multiple branch and regional drainage before mining.It has played an important role in ensuring the safe production of coal mines.However,with the increasing of borehole depth and borehole diameter,the inherent limitations of sliding directional drilling technology and the cable MWD technology gradually were revealed.In view of problems that how to increase efficiency of deep large diameter holes and how to drill in complex formations in underground coal mine,the technology of drilling combined rotary with direction was developed in this paper,in which the trajectory controlling mechanism and the mechanical characteristics of drilling combined rotary with direction were analyzed.Meanwhile the mud pulse wireless MWD(Measurement While Drilling)system for underground coal mine was designed,which can improve the capability of the underground directional drilling equipments in order to ensure the security of coal mine production.First of all,based on principle and characteristic analysis of drilling technology combined rotary with direction and the drilling tool cutting principle at hole-bottom in composite directional drilling was studied.The prediction model of borehole trajectory of non-stabilizer BHA which is fixed angle of bend was established,and based on simulation,the drilling side force increases as downhole motor angle,side force of bit and WOB increases and decreases as borehole expansion rate increases;the inclination deviation increases as downhole motor angle and side force of bit increases and decreases as WOB and borehole expansion rate increases;the head speed and hole inclination have little effect on the change of drilling trajectory during drilling combined rotary with direction.In conclusion the trajectory during drilling combined rotary with direction can remain stable,when 1.25 downhole motor is applied with 15 kN WOB and borehole expansion rate 10%.At the same time,the vibration model of drill string was extracted,and the rock cutting process of bit-drill string system was simulated.During the rock cutting simulation process of bit-drill string system,three-dimensional model of drilling combined rotary with direction is established,Based on the Abaqus/Explicit solver of explicit central difference algorithm,Resonance phenomenon of BHA would not occur,Periodic stress and strain state between the BHA and the stratum is quantitatively analyzed,which can provide reference for drilling process parameter selection.Secondly,according to the special construction environment and drilling technical requirements in underground coal mine,a set of mud pulse wireless MWD device suitable for coal mine condition was designed including the signal measuring module,the signal control module,the signal emission module,and the signal receiving and processing module.And the mud pulse generator of a diameter of 73 mm for 96 l/min low-emission was developed,the pressure pulse amplitude calculation method is put forward according to design principle of valve head,it is concluded that the greater the radius of valve head,the higher the pressure pulse amplitude,meanwhile the influence factors of mud pulse signal transmission is analyzed,it is concluded that downhole pulse signal amplitude increases as transmission velocity and pipe diameter increases,and decreased as the transmission frequency increases,which can provide reference for working parameters setting and the selection of drilling parameters f in underground coal mine application.Finally,the drilling technology combined rotary with direction and mud pulse MWD wireless device were tested in three fields,which verified the research results of this paper.The research of drilling technology combined rotary with direction and wireless MWD technology can be used to guide drilling engineering practice of field gas extraction,and also has certain reference value for further research and application in related fields.