LAUSR

Abstract Running casing in extended-reach well (ERW) can be extremely difficult because of high drags. Once running casing is hindered by high drags, a special operation, aggressively working casing string, sometimes is employed to help casing overcome the high drags. During this operation, drillers first pick casing string up to a certain height and then slack it off rapidly (or drop it), so that casing string seems to “fall” from that height with relatively high speed. Because of the kinetic energy, casing string is more likely to overcome high drags and reach the target depth (TD). However, the operation also has many uncertainties. For example, whether casing string can really overcome high drags is hard to predict. Moreover, the operation sometimes is violent and may cause safety problems. To study this operation, a new drag model is built to describe the behavior of casing string during aggressively working string. The model is an improved soft string model which considers dynamic motion of casing. The model is able to calculate forces and motion of casing string in falling process during aggressively working string. Two case studies are presented where casing string was aggressively worked to overcome high drags. Mechanical behavior of casing string in each case is studied and the safety issues are discussed. Finally, suggestions on this operation are also proposed.