DESIGNING A DRILLSTRING

摘要

Designing a drillstring in for use in a wellbore, such as a deviated or horizontal wellbore, particularly with application to extended reach wellbores. Method comprises determining the downhole weight-on-bit transmitted by a drillstring by determining a baseline tension profile and baseline torque profile in a drill string rotating off-bottom, and then using such profiles in conjunction with a selected surface weight-on-bit slack-off value to calculate a drillstring tension profile and rotating torque profile with the bit on bottom and having weight applied thereto. The method includes buckling limit checks and rig operational limit checks to determine if sufficient torque and DWOB can be transmitted through the drillstring, and to determine whether the drill string remains operable even though portions thereof may be in a buckled condition.