AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
The Discovery and Exploration Potential of the Eocene-Miocene Shelf Margin Deltas in the Baiyun Sag of Pearl River Mouth Basin, South China Sea
(1) CNOOC Research Center, Beijing, 100027, Beijing, China.
(2) CNOOC Limited, China, Beijing, 100010, Beijing, China.
(3) China University of Petroleum (Beijing), Beijing, 102249, Beijing, China.
The Baiyun Sag is a subunit of the Pearl River Mouth Basin and is situated in the deepwater region of the north slope of the South China Sea. The exploration potential of the subunit is demonstrated by the recent discovery of the LW3-1 gas field and other gas discoveries along the north slope of the sag. To bring exploration in the sag one step further, a better understanding of the depositional environments and characteristics of the Oligocene-Miocene successions is critical.
Based on an integrated analysis of well log, core, and high-resolution 3D seismic data, a series of Oligocene-Miocene shelf margin deltas were discovered recently in the sag. During Oligocene, these deltas prograde primarily under late lowstand conditions and delta-front deposits were well developed. Shelf break during this time was controlled to a significant extent by normal faulting, and the system grew towards the uppers slope with distinct “S” geometries. During Miocene, in contrast, depositional mechanism changed and there were more gravity-flow processes in the extended space between the outer shelf and the upper slope. Typical depositional elements identified in the delta-front successions of the shelf margin deltas include distributary channels, mouth bars, tongue-shaped sediment-failure and sediment-gravity-flow deposits, and shelf-slope channels.
Siliclastic supply from the feeding rivers of the shelf margin deltas, coupled with the carbonate source from the nearby Dongsha Uplift, provides sufficient material not only for the growth of the shelf margin deltas but also for the development of their linked deepwater system.
The integrated data set and recently exploration results along the LH34 and the LH29 districts demonstrate the genetic link between the shelf margin deltas and the deepwater systems further basinward, indicating that there is huge exploration potential in the sag.