Sedimentary Facies Distribution and Petroleum System Identification on the Deepwater Phu Khanh Margin, Offshore East Vietnam

Frankowicz, Edyta; Reemst, Paul; Kocher, Thomas; Henstra, Gijs; Steffen, Daniel
Shell International Exploration & Production, The Hague, Netherlands.

The Phu Khanh margin is a frontier area located offshore East Vietnam, resulting from multiple rifting associated with the opening of the South China Sea from the Eocene to Middle Miocene. It is offset by N- to NEE-trending extensional faults forming horsts and grabens, and it is thought to contain multiple clastic and carbonate plays and multiple source rocks of lacustrine and paralic nature.

The existence of a working petroleum system in the Phu Khanh margin has been confirmed by the presence of oil slicks and DHI's. Only a few wells, which targeted Miocene carbonates and proved oil charge, have been drilled in the Phu Khanh shelf. There is a low likelihood that the carbonates occur further outboard, where both syn- and post-rift clastic plays will be the focus of potential future exploration.

This study discusses the distribution of sedimentary facies and associated elements of a possible petroleum system in the deepwater Phu Khanh margin. The study was carried out based on 8000 line km of sparse 2D seismic grid, projected well information and potential field data. Based on the derived tectono-stratigraphic framework the key play elements were assessed.

A Paleogene syn-rift clastic play and an Oligocene-Middle Miocene transitional play were identified as key exploration targets. These plays are not proven, but inferred from analogues in the adjacent basins (e.g. the Nam Con Son basin). Several distinctive seismic facies have been inventoried and assigned to represent specific litho-stratigraphic facies. The facies have been put into the tectono-stratigraphic and depositional megasequence framework, which is characterized by deepening of depositional environment in individual grabens from typically continental (Paleogene syn-rift) through shallow marine (Oligo-Miocene drift phase) to deep marine in the Plio-Pleistocene. Distribution of source rock and reservoir intervals was then identified for each play by mapping the gross depositional environment based on seismic facies interpretation.

Potential lacustrine source rock and reservoir are limited to existing grabens. Occurrence of a potential paralic source rock and clastic reservoir facies is more widespread. Timing of charge remains poorly constrained and charge presence and maturity are the key risks for both plays.

The seismic facies interpretation methodology used in this study can be also applied in other continental-rift to marine-drift passive margins.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012