Research On The Correction Methods Of Borehole Trajectory And Calculation Of Error Ellipsoid

Infill well and cluster wells become regular stimulation means, but face a serious borehole collision problem. Connected drilling is available to CBM development and relief well construction, while needs borehole intersection. These technologies put forward higher request to description precision of borehole trajectory.The purpose of this paper is to make calculated trajectory closer to real trajectory through corrections of azimuth and inclination, and estimate uncertainties of borehole through error ellipsoid calculation. Firstly, paper gives a list of error sources for compass survey,gyrocompass survey and MWD, and confirms their nature and magnitudes. Secondly, for the purpose of correcting azimuth, paper studies magnetic declination correction for compass survey and MWD, and studies magnetic reference correction for MWD; Thirdly, for the purpose of correcting inclination angle, paper calculates projection of instrument misalignment error on inclination plane with continuous beam column theory, and estimates the residual inclination error after correction. Fourthly, paper studies calculation of error ellipsoid by analyzing WdW error model and Industry Steering Committee on Wellbore Survey Accuracy(ISCWSA) error model, and improves WdW error model by modifying instrument misalignment error. Finally, paper evaluates the effect of improved WdW model,and researches the influence of azimuth and inclination correction on borehole position uncertainty. This paper establishes effective methods of correcting azimuth and inclination,improves the WdW error model, and points out the difference of borehole position uncertainty between before and after angle correction. The paper has pratical significance to improve description precision of borehole trajectory.