China's deepest offshore oil well put into operation

China's first independently designed ultra-deep large-displacement well, the Enping 21-4 oilfield A1H well, has commenced operations. The well is located about 200 kilometers southwest of Shenzhen in the South China Sea and has a tested daily production capacity of over 700 tons of crude oil.

The A1H well has a drilling depth of 9,508 meters and a horizontal displacement of 8,689 meters, making it the deepest well in China’s seas and setting a record for the country’s horizontal drilling length, according to offshore operator China National Offshore Oil Corp. (CNOOC).

The Enping 21-4 oil platform. Photos courtesy of CNOOC

This marks a successful breakthrough in the technical bottleneck of 10,000-meter-class large-displacement wells, placing China’s ultra-deep and ultra-long drilling technology at the forefront of the world.

The Enping 21-4 oilfield, where the ultra-deep well is located, has an average water depth of about 86 meters and is classified as a small sandstone marginal oilfield. Traditional exploitation methods would require the construction of new offshore production platforms or subsea wellheads and other facilities, which is costly and time-consuming. CNOOC has utilized the unmanned Enping 20-5 oil platform, located 8 kilometers away, for extended-reach drilling, which can efficiently develop the oil and gas resources of marginal oilfields.

Engineers at work at the Enping 21-4 oilfield.

Marginal fields refer to smaller oilfields that usually remain unexploited due to their limited reserves, lack of infrastructure in the area, and prohibitive development costs.

Gu Yongbin, chief engineer of CNOOC’s Shenzhen branch, said that by relying on existing platform facilities and using extended-reach drilling technology, the company has precisely drilled underground oil reserves several kilometers away and broken through the barriers to developing marginal offshore oilfields and promoting the development of the Enping 21-4 oilfield.