BEIJING, March 8 (Reuters) - China's $1-billion deepsea drilling rig, the first of its kind designed and built at home, has returned to work in a South China Sea gas field after nearly two months of repairs, rig owner China National Offshore Oil Company said on Friday.
The rig, "Offshore Oil 981", was being chartered by Canada's Husky Energy, operator of the Liwan project in the western part of South China Sea, a major offshore gas discovery, industry officials have said.
"Leaks have been repaired and maintenance works finished. Offshore Oil 981 has returned to works at Liwan 3-1 gas field," CNOOC, parent of CNOOC Ltd said in an email.
CNOOC told Reuters last month that "minor leaks" were found at one water pump room on Dec 31 during routine checks, possibly caused by the release of structural stress in the early days of the rig's operation.
CNOOC did not give a final analysis for the leaks. Industry officials with knowledge of the matter said cracks were found in one of the rig's four steel columns that had led to water leaks, which could be due to steel problems or design faults.
The rig, officially launched last May, was dedicated to exploring the South China Sea, in which China, Vietnam, the Philippines, Taiwan, Malaysia and Brunei have overlapping claims.
Before Husky chartered the rig it had drilled several deepwater wells for CNOOC Ltd, industry officials said.
The rig was built by China's Waigaoqiao shipyard and has a dual registration, with the China Classification Society (CCS) and the American Bureau of Shipping (ABS). It is owned by CNOOC and operated by China Oilfield Services (COSL).