Thursday, July 6, 2017

South China Sea Oil Reservoir Prospects

In the middle of high tense of geopolitic, South China Sea remains highly potential for hydrocarbon reservoir. China has been showing military power to secure South China Sea , which is disputed by Vietnam, Malaysia, Brunei. This essay provides geological & geophysical general approach to understand the prospect of hydrocarbon in South China Sea.

Study area is located in south of Hong Kong

Geologic cross section from North West to South East

The region lies in about 100 m (230 ft) of water in the Pearl River Basin in the South China Sea, some 100 km south of Hong Kong.
Hydrocarbon-bearing sands were discovered in this region in 1986, and a field there now produces 80,000 barrels of oil per day. Two years later, a wildcat (well A) was aimed at a Miocene carbonate reef at the margin of the field and underlying fluvial deltaic sandstones of Lower Miocene age called the Zhuhai. Log and well test data showed that the 30-m (100 ft) thick sandstones were well sorted, porous and oil bearing. The spatial distribution of the sandstones was thought to have been controlled by the overlying reef, which seeemed to act as a caprock. The reef itself was dry, but its extent was uncertain. 
A second well (Well B) was drilled 11 km southeast of the wildcat to explore the lateral extent of the reef. The well encountered a carbonate platform and some reef overlying a thinner Zhuhai sandstone, but indicated poor hydrocarbon shows. 
A third well (Well C) was then drilled on the opposite side of the reef, 3 km northwest of the wildcat, but this also gave dissapointing results despite finding the reef and the sand. 

The interpreters derived an acoustic impedance profile in the wildcat well and the transformed the surface seismic section into an acoustic impedance section over the entire target area. Sands are light green to yellow, while carbonate is blue. It appears that the hydrocarbon-bearing sandstones in Well A pinch out about 350 m to the nortwest, explaining why Well C, over 3000 m away and off the section, tested dry. 

However, the sandstone extends farther southeast but is thought to undergo a facies change, becoming tighter before it reaches Well B, also off the section, as diagenesis increases. The impedance section shows that further drilling should be concentrated close to the back reef area.

(source: Oilfield review , April 1992)


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