Design And Study On Drill String's While-drilling Parameters Monitoring Sub

With the increasing difficulty of oil reservoir drilling and production,the problems of frequent accidents,long drilling cycle and high drilling cost in deep and ultra-deep wells are becoming more and more serious,which put forward higher requirements for near-bit drilling string's parameters monitoring.The existing MWD tools mainly focus on directional data and stratigraphic parameters,which lack of comprehensive monitoring of drill string's parameters.Firstly,this paper studied the measurement method of the near bit drill string parameters while drilling.Based on the analysis of the stress state of the drill string,the electric bridge measurement method is used to measure the drill string's drill pressure,torque and bending moment,and the theoretical derivation and error analysis of the output voltage of the patch scheme are carried out;the sensor layout scheme is designed for the downhole installation environment to realize the drill string vibration and speed while drilling measurement;The pressure inside and outside the drill string and bottom hole temperature are monitored by using sensors adapted to the downhole environment and designing special downhole installation structure.Secondly,this paper studied the mechanical structure of monitoring short sub.Aiming at the problem of narrow installation space and complex stress condition in downhole,the sensor and circuit board are designed as centering installation structure without destroying the overall structure of the tool;the key components of the tool are analyzed by structural strength theory,and the equivalent stress under the ultimate load is checked,as well as the shape and size of the tool line holes are improved by means of finite element simulation software.Aiming at the underground high pressure environment,O-ring sealing scheme is designed and simulated by finite element method.Finally,a down-hole while-drilling measurement system was developed with 0.40 m V resolution and 5k Hz sampling frequency.Complete the circuit design of the system,design the corresponding down-hole conditioning circuits for the output signals of bridge,rotation speed,pressure and temperature;and take STM32F103 as the control core to realize the accurate acquisition of these signals.At the same time,design the down-hole voltage-stabilized power supply circuits to solve the power supply problem of the down-hole electronic system.Based on the functional requirements of the circuits' structure and the characteristics of STM32F103,the corresponding acquisition program and digital filtering algorithm are developed for different signals.The communication function between each module is completed by 1-wire way,as a result of the acquisition,processing,storage and communication of underground signals are realized.