Abstract:
When drilling petroleum well into the reservoir section in the Gulf of Thailand, the bit walk rate has to be kept at minimum because of the narrow target. Meanwhile the steerable tool cannot be used to directly control the hole direction because it cannot function in high temperature as in the Gulf of Thailand’s reservoir. More than five percent of the wells drilled per year were pulled out of hole due to unable to keep the walk rate into the acceptable range. Then different bit design or different bottom hole assembly (BHA) was replaced to assure hitting target zones. This study was performed to address the factors that have influence on the bit walk, summarize their effects, and create the walk rate prediction table that can be used as a guideline for better pre-job planning such as BHA design and bit selection to reduce the number of trips for assembly changes which means saving cost in drilling wells. The actual field data of 495 wells drilled from year 2006 to year 2008 which composed of 17,625 survey station points was used in the study. By using the statistical tools including percentile, median and mean, the effect of each parameter to the walk rate could be defined and compared, and the walk rate value could be predicted. The study results indicated that the walk rate was influenced by the bit model, hole angle, AGS setting, RPM WOB, extension length and TVD depth in an average value of 0.26, 0.24, 0.20, 0.19, 0.18, 0.161 and 0.160 deg/100ft respectively. The walk rates predicted from this study were very close to the actual walk rates with less than 0.05 deg/100 ft discrepancies.
