Research On Error Compensation Of Equivalent Rotation In MWD

In resource exploration and exploitation,it is necessary to continuously measurement the motion parameters of drilling tools while drilling,that is,measurement while drilling(MWD).Navigation equipment is indispensable for MWD system.The MWD system needs navigation equipment to measure the motion parameters of the drilling tool in real time,so that the drilling tool can drill along the established trajectory.Attitude measurement while drilling based on inertial navigation technology is a completely autonomous,free from external interference and large amount of output information.It can provide more complete motion parameters for drilling tools all day and all weather,which makes it widely used in MWD.However,the error of inertial device and the harsh environment during drilling have a serious impact on the accuracy of attitude information of drilling tools.Therefore,how to process the interference signal in MWD and the error of inertial devices becomes the key problem to improve the accuracy of MWD.In order to improve the attitude measurement accuracy,an equivalent rotary error compensation system of MWD is designed based on the existing researches.Specific research contents are as follows:(1)The hardware system of MWD is designed by employing inertial measurement device and magnetometer to collect triaxial accelerations,triaxial angular velocities and triaxial magnetic field intensities of the drilling tool.(2)The constant drift of inertial devices has a great influence on the accuracy of attitude calculation.But the MWD system is small in size and has limited internal space,it is difficult to achieve error compensation by adding a rotating mechanism in the measuring cylinder.Therefore,based on the analysis of the existing rotation schemes,an equivalent rotation modulation scheme is constructed by using the heading maneuver of the drilling tool to compensate the constant error of the inertial device.(3)In view of the problem that the output of accelerometers and magnetometers are susceptible to vibration and random magnetic interference,the collected signals are extracted by employing Coriolis transfer equation,and the gravity acceleration and magnetic field intensity which are required for the attitude calculation of drilling tools are obtained.(4)There are still mutation points in the signal after separating harmful components.Therefore,catastrophe theory is introduced to discriminate the catastrophe signal.Then,based on Kalman filter,a catastrophe filtering algorithm is designed to process the abrupt gravity acceleration and geomagnetic signals to compensate for the error of attitude measurement of drilling tools in the harsh environment.