A vertical casing-exit operation in the high-inclination cased hole of Well Su 5-1H, Sulige Gas Field

Well Su 5-1H in the Sulige Gas Field is the first well having vertical casing-exit operation conducted in the wellbore with an inclination angle of over 80° in China, with such challenges as difficult running-in of wireline instruments and the whipstock or hard vertical casing cutting due to the gravitational force on the cone mill bit. After overcoming such difficulties, however, we have devoted only 19 hours in one trip to successfully cut a casing window in the end. After 6 hours of casing cutting, 2. 5 m footage was finished and lots of iron cuttings were observed. Then, after 12 hours of continuous working, a large amount of sand and cement were seen, from which a successful casing-exit operation could be announced. Finally, the BHA was then tripped out after window trimming was done for several times. From this successful experience, a few good lessons are drawn herein. (1) The one-time whipstock is helpful for the vertical casing exit, and the double-cone milling bit can finish the casing window opening and trimming in one trip. (2) Good reparations for whipstock setting and casing-exit job are vital in the whole process. (3) Each operating parameter at every step is well designed. All the above will provide good reference for the casing-exit operation in similar wells.