Analyses of the Cause of Casing Sticking in Well ZX105 and the Techniques of Freeing the Sticking

Well ZX105 is the first exploratory horizontal well drilled in Zhixinchang structure in western Sichuan. This well, targeted the lower Shaximiao formation, was designed to drill to measured depth of 3,726 m (TVD 2,506 m). The designed length of the horizontal section was 1,001 m. The casing for the second interval was run and got stuck at 2,847 m when running lift sub and casing hanger to move the casing string. It was believed, through analyses, that it was a pressure differential sticking, and deficiencies of the casing program was the main cause of the sticking. It was also believed that the depth at which the casing for the first interval was run was not enough, and the point at which the casing got stuck is 214 m into the horizontal section, the weight of the casing string in the upper section is not enough to push the casing inside the horizontal section to move forward. The high positive differential pressure at the bottom of the hole thus caused the casing string to get stuck. Based on the analyses, it was decided to lower the mud weight, soak the stuck point with pipe freeing solution, and pressurize the annular space. The stuck casing string finally got free with these measures. This is the first time the stuck pipe gets free in horizontal drilling in the west of Sichuan, and the practice has provided valuable experiences for the development of the target zone, the Lower Shaximiao formation in Zhongjian area, western Sichuan.