Long Tien Nguyen, vice president of PetroVietnam E&P, answers questions during the topical breakfast "Understanding the Challenges of Vietnam Fractured Basement Exploration, Drilling and Production" at OTC on May 5. (Photo courtesy of CorporateEventImages.com)
HOUSTON—In the Cuu Long Basin offshore Vietnam, there is world-class rock with remaining potential of 3.7 Bbbl of oil. There are 16 producing fields in the basin and 10 undeveloped discoveries. Tapping into the fractured granite basement to produce that oil has led to several innovative solutions.
At the topical breakfast “Understanding the Challenges of Vietnam Fractured Basement Exploration, Drilling and Production” at OTC on May 5, Nguyen Tien Long, vice president of PetroVietnam E&P, listed some challenges in the basin: no porosity in the fresh granite basement; fracture network and weathering create porosity; distribution of connected fracture network; fracture orientation for well-path optimization; and impact of extrusive rock to the quality of the fractured basement reservoir.
There is a lot about the granite basement that is difficult and challenging, said Pham Tien Dung, president and CEO at PetroVietnam Drilling and Services. For example, drilling into the fractured granite basement caused lost circulation, and a solution had to be devised.
“We overcame difficulties with new techniques and solutions, including well design and bit improvements,” he said. “The key for success is to set the shoe on top of the basement, run casing and cement it. Then we use an 8½-in. bit to drill into the basement.”
To solve the lost circulation problem, seawater was used as the drilling fluid in the granite. Some fractures could be as much as 0.5 m (1.64 ft) so circulation doesn’t work. Total lost circulation in the granite could be as much as 2,000 bbl/hr. “The beauty of basement drilling is that if you have this problem, then you may have production,” he added.
Improvements in Baker Hughes’ bit designs and mud motors improved ROP in the granite from 7 m/hr (23 ft/hr) in 1992 to 10 m/hr (33 ft/hr) today, he continued.
The operator doesn’t have to worry about the well collapsing when running the completion into open hole in the granite. Swell packers with sliding sleeves are used to isolate above the water zones without cutting into production zones.
“We’re drilling with an 8½-in. bit in the granite section. The horizontal section is about 2,700 m [8,858 ft] at an 85-degree deviation,” Dung said. “A lot of marginalized wells have become more predictable.”
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