July 18, 2019
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Identify all of the different methods of correcting survey measurements and their applicability for different well trajectories and different latitudes.
This is a familiar area as I was required to travel to Venezuela to overcome survey measurement area in the land operations where they were drilling numerous multi-lateral extended reach wells. The driller on the drilling floor did not understand why he was getting high torque in his operations and it turned out there were metal cuttings coming back over the shakers. The metal cuttings weren’t reported immediately and meanwhile they realized they had drilled through another well. The problem was they didn’t all have the same software on their systems and the surveys they had were referenced to different norms. Continuity is key! I had to re-vamp their survey software and re-load the surveys referencing the correct North in order for them to know where the wells were that they were drilling. References from the northern parts of Canada are greatly different from references near the equator. Canada has a higher degree of error to magnetic north compared to references from the area of the equator. As well, the further away from your drill center (or rig location) the more complex your survey results can be. We have seen errors on highly deviated deep wells as high as 6% offshore Canada compared to errors in surveys from as low as 1 to 3% in other areas nearer to the equator. These errors can cause a geological mapping problem leading to mis read results by the geo-scientists. The best way to correct survey measurements is through software specifically to the area in which you are operating. Measurements can be in error as well due to the magnetic nature of the formations you are drilling through. The most effective way in correcting survey error is dropping a survey downhole, pulling it to surface at least to the first casing point and verifying this with the downhole tool measurements. If you are unable to correct the hand held survey to electronic survey the software being used needs to be checked as well as the survey tools. If you are unable to reference your center location correctly the error in drilling further away from the center only significantly increases the survey error.
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