The Development Of MWD Measurement Sub For Downhole Engineering Parameters

With the development of drilling technology, the traditional ground-based method of measuring WOB, torque and other engineering parameters can not truly reflect the actual situation underground.The MWD system can real-time measure WOB, torque and other engineering parameters near the drill bit to truly reflect the actual situation underground.So MWD technology is increasingly being applied to the drilling project.This article frist introduced the overall structure of the pre-designed downhole MWD joint.And introduced the principle of strain gauge measurement of stress, analysed the relationship between the strain and the stress on the joint from the point of view of mechanics of materials. This article analysed the theory output of the strain bridge when the WOB and torque coexists.Then made a theoretical analysis of error on a single strain gauge which caused by placement errors of the strain gauge when the WOB and torque coexists.Secondly, this article improved the original hardware circuit, increased auto-zero function to the signal acquisition channel and function of automatic conversion to the scale. This paper re-designed both the occurrence circuitry of the sine wave signal which powered the strain bridge and the power control circuitry of amplification circuit boards. This paper redraw the PCB circuit board while regularly programming each module and realized the function of data storage.Finally,this article debugged the improved PCB board. Through debugging the auto-zero circuit, low-power time-sharing power supply circuit, Wien-bridge sine-wave signal circuit meeted the design requirements. The signal acquisition channel AD converter meeted system requirements. The MWD joint can realized functions of signal acquisition, storage and serial communication.The downhole engineering parameter measurement system works with 16-bit AD conversion, the resolution can achieve 0.04mV; the serial flash memory of the system up to 32Mbit, can store data to 190 hours; the system have low-power plans to economize the battery capacity; the system also have auto-zero channel and automatic range adjustment to increase the measurement accuracy.