Page | 79
Points to Ponder
Applying magnetic interference corrections can double the accuracy of the wellbore placement. However, here are 10 questions to ask of the correction report.
1. What was the source of the background field data 2. Has it been updated by a suitable global magnetic model 3. How much of the original data was rejected 4. What were the rejection criteria 5. Are we sure the data used was all from one BHA run 6. What was the typical size of correction applied 7. What did the Bt and Dip look like before and after correction 8. Is there a significant bias in either Field or Dip from the background field 9. What was the variation in attitude during the BHA run (too little can lead to unstable results) 10. Do I get the same answer if I only use half of the data
15. o c ngfo p ndW ln ch
15.1 Forces on the drillpipe
It has not been routinely included in survey procedures to estimate and remove the mechanical or thermal expansion of the drillpipe and yet clearly the weight of the BHA itself and the drillpipe suspended below any section of pipe will stretch it, as will any increase in downhole temperature from that observed at surface where the drillpipe length is measured before deployment.
Figure 68: Forces acting on a finite element of drillpipe.
Made with FlippingBook flipbook maker