CNOOC hits 80% drilling success mark in 1997

Nine major offshore discoveries recorded

Wang Ming Wu
Contributing Editor
Beijing

China National Offshore Oil Company (CNOOC) had an unexpected bumper year in 1997. The difficult CNOOC target of 30 million tons of oil production per year, expected by the year 2005, was realized in 1997, eight years ahead of schedule.

Nine hydrocarbon-bearing structures were discovered during 1997. Exploration and development drilling had an 80% success ratio. Three of the new geological structures were breakthroughs.

• Pearl River Mouth: The first and second breakthroughs were made from two high-yield wells drilled in the Zhusan-Wenchang depression of the Pearl River Mouth. A productive hydrocarbon zone was found that may lead to further development. Since 1995, CNOOC has drilled continuously in the area. Five self-financed wells resulted in four discoveries.

The Wenchang 13-1-1 and 13-2-1 wells yielded a flow of 2,000 tons/day and 900 tons/day, respectively. The discovery zone is similar in time sequence, oil quality and structural type to the oil-bearing horizons in Nanhai East's offshore fields. CNOOC now controls 50 million tons of proven oil reserves from this geologic zone.

The third breakthrough was made from the Donghai Basin's Lishui depression in the East China Sea. The Lishui 36-1 structure is known for yielding high natural gas flows.

At present, CNOOC has proven reserve additions of 176 million tons of oil and 8.6 billion cu meters of gas from new fields.

The company already controlled 175 million tons of oil-in-place (oip) and 320 billion cu meters of natural gas from older fields reviewed. This has laid a good foundation for realizing the target of 30 million tons of oil production by 2005.

• Bohai: The Zhaodong concession consists of six blocks covering 197 sq km. The first external cooperation concession in the north of China lies in the shallow waters east of Zhajiabao in the Dagang oil field.
• Boxi project: Phase I of Boxi oilfield project came onstream November 1997. This is a start towards the 10-million-ton production target and will advance the Soxi-Bonan system development. Fields now onstream from the project include: Qikou 18-1: Production began in November 1997; Qikou I7-3: Production began in December 1997.
• "C" block discovery:Well C-4 lies in four meters of water in the C block of Zhaodong concession. Bohai 7 completed the well near the end of last year after drilling to a TD of 2,741 meters in 34 days. Eight oil pays and one gas zone were found in the Shahejie formation (Mesosoic). Total pay thickness is 86.5 meters.

The well tested over 2,000 tons of oil per day, 130,000 cu meters per day of natural gas and 170,000 cu meters per day of associated gas. The partners, Apache and Rowan, announced that C-4 is a world-class high-yield test. Seven high-yield oil wells have been drilled in the Zhaodong concession.

• Jinzhou 9-3 delayed:CNOOC established new records for fast drilling on the Jinzhou 9-3 development. Chinese offshore drillers came to Bohai after gaining experience from Qikou 1O-1, Qikou 17-3, and Suizhong 36-1 (J block) oil fields. The Jinzhou 9-3 oil field is due onstream later this year.

There are two platforms in the field with 46 well locations. Thirty wells in the western district must be completed before 10 July 1998 to guarantee that the field can come onstream this year. Wells are being drilled by the Bohai 5.

Construction faced a difficult test due to the severe winter and ice. Four development wells doubled as appraisal wells. Each well faced a difficult 1,000+ meter sandstone interval and extended-reach drilling required a 63! angle with a 2,313-meter reach.

• Nanhai Huizhou find: CACT operator group made a new discovery, Huizhou 26-2-1, in the Pearl River Mouth. The discovery well was drilled in late 1997, with official announcement before the end of the year.

The well is in Block 16/08, 139 km southeast of Hong Kong, and was drilled to 3,350 meters. The well is 8,500 meters from the Huizhou 26-1 platform. Drilling results showed that Huizhou 26-2-1 has a oil-bearing formation 106 meters thick. The well tested 1,000 tons per day of crude oil with a specific gravity of 0.79-0.83!, similar to that from Huizhou 21-1 oilfield.

Huizhou 26-2 is a reverse drag anticline located on the southern fringe of Zhu 1 depression. The discovery was made from 3D seismic data on Blocks 16/08 and 16/19. Covering 1,190 sq km, it is the largest survey gathered to date in China.

• Wencheng flows: The Wenchang 13-2-1 flowed 900 cm/d of crude oil during the last quarter of 1997. The well is another important discovery in Nanhai, following the Wenchang 13-1 structure and high-yield, high-quality oil and gas from the Wenchang 13-1-1 well. The Wenchang 13-2 structure is adjacent to Wenchang 13-1, Wenchang 8-3, and Wenchang 19-1 oil and gas bearing structures.

This is another foothold for jointly developing oil and gas fields in Wenchang waters and is an important guarantee of resources for setting up production capacity in the Zhusan depression. Preliminary reserve predictions indicate over 20 million tones of oil in place (oip).

Nanhai West continued drilling Wenchang 13-1-2 and Wenchang 13-2-2 appraisal wells to determine reserves.

• Lufeng transition: Lufeng 22-1 was discovered in 1986 and is the ninth oilfield of Nanhai East Corp. It is a marginal field lying in 300-meter water depths of Block 17/22. The field initially failed in development and was transferred due to drilling difficulties.

Statoil began drilling Lufeng 22-1 at the end of 1996 and completed it by mid-1997. The wells were completed by the Nanhai 5 later that year, after which an installation ship arrived to construct the facilities. The multipurpose shuttle tanker, Munin, arrived after modification in Singapore. The field came on production in December 1997.

• Donghai breakthrough: A major natural gas discovery was made in Donghai Block 32/32 by cooperative drilling efforts between CNOOC and UK-based Primeline Petroleum Corp. The Lishui 36-1-1 well tested 28,000 cm/d of gas and 18.7 cm/d of condensate in the last quarter of 1997. This was a significant exploration breakthrough. Block 32/32 lies in the Taibei depression in the Donghai Continental Basin, 150 km southeast of Wenzhou City, Zhejiang Province.

This breakthrough was an answer to a problem that had not been resolved for years. It lead to the identification of the oil sourcing and trapping mechanism in Donghai.

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