Updated Sequence Stratigraphy of Blocks A & B, Song Hong Basin, Vietnam

Blocks A & B are located in the Song Hong Basin, offshore, Northern Vietnam in a water
depth of 25 to 30 meters. Company C is the operator with a 50% of interest. In 2004,
Company C drilled the first commitment well (Well 6) and discovered minor oil and gas
in the Middle Miocene sand. The subsequent well (Well 7) was drilled in middle 2006
which is turned out to be a dry well. The third exploration well drilled in end 2006
encountered significant amount of gas in the Middle to Late Miocene sands.
Plate tectonic reconstruction and geodynamic evolution showed that the Song Hong basin
is a rift basin that was formed in the late Eocene/ Oligocene time. The basin formation
and evolution is very closely related to the strike slip movements of the Red River Fault
Zone following the collision between the Indian Plate and Eurasia Plate in the Oligocene
time. The basin had undergone a series of extensional and compressional events that
provided the main structural framework for hydrocarbon trapping mechanism in the area.
Four key seismic lines have been selected to identify sequence boundaries and to produce
geoseismic sections. The study has identified six sequence boundaries that separated the
depositional package into seven sequences. Two horizons namely, Lower Miocene and
Base Pliocene were interpreted. Three paleogeographic maps and illustrated 3D models
were produced. Based on the paleogeographic maps, Composite Common Risk Segment
(CCRS) maps were produced and the results from the risk mapping suggest that these two
blocks are in the medium to high risk zone in terms of petroleum exploration.
A working petroleum system is believed to be present in the basin based on a couple of
discoveries have been made in Blocks A & B and the adjacent blocks. The first package
in the early Oligocene sequence are believed to be deposited in the lacustrine setting that
provided the main potential source rock in the area. The peak of the hydrocarbon
generation and migration is believed to be in the middle Miocene time, which post-dated
most of the structure formation. The main reservoir is the karstified and fractured pre-
Tertiary carbonate rock. Other potential reservoirs are from the fluvial to deltaic in the
Oligocene section and coastal, deltaic to shallow marine sands of Miocene sections. The
seal is provided by intraformational shale and reinforced by a thick layer of regional
Middle Miocene shallow marine shale. The traps are associated with the formation of
syn-rift, horst and grabens and a latter series of inversion events that took place during
the evolution of the Song Hong basin. Potential stratigraphic traps such as onlapping
shallow marine sands and basin floor fan may also present. The area to the south of Block
B warrant further investigation to delineate the potential of possible deposition of basin
floor fan during sea level drops in the middle Miocene time. Nine play types were
identified based on previous study and of the nine plays; five had been tested by previous
wells while the four new plays will be investigated in the ongoing explorations
programmed.