High dogleg severity, wear ruptures Chinese casing string

A combination of high dogleg severity, swelling shales, and internal casing wear led to a ruptured casing string in the Tarim oil field of the Xinjiang Province, China.Acting upon this information, personnel from China National Petroleum Corp. evaluated the events that led to the incident and formulated guidelines to avoid such occurrences in the future.BackgroundThe accident occurred in January 1997 after testing well X1 for 15 hr. Over the next 12 hr, crewmembers reverse-circulated clean water, with some chemical additives (KZ-01), at a pump pressure of 12-18 MPa.Subsequently, a total of 162 cu m of mud (mud density = 1.24-1.34g/cu cm) was recovered. However, engineers calculated that 6...

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