Controls on Seismic-Scale Geometries of Mixed Carbonate-Siliciclastic Reservoirs: Example from the Triassic Nanpanjang Basin, South China

Minzoni, Marcello¹; Enos, Paul²; Lehrmann, Daniel J.³; Wei, Jiayong⁴; Yu, Meiyi⁵; Payne, Jonathan⁶; Kelley, Brian⁶; Meyer, Katja⁶; Schaal, Ellen⁶; Li, Xiaowei^5
1Shell International E&P, Houston, TX.
²Department of Geology, University of Kansas, Lawrence, KS.
³Department of Geoscience, Trinity University, San Antonio, TX.
⁴Guizhou Bureau of Geology and Mineral Resources, Bagongli, Guiyang, China.
⁵Department of Resources & Environmental Engeneering, Guizhou University, Caijiaguan, Guiyang, China.
⁶Department of Geological & Environmental Sciences, Stanford University, Stanford, CA.

Comparative analysis of platform evolution recorded along multiple 2D platform-to-basin transects of the Triassic Yangtze Carbonate Shelf and several isolated platforms in the Triassic Nanpanjiang basin, south China, indicates that laterally-variable tectonic subsidence, rate of basinal clastic deposition at the toe of slope, and changes of carbonate factory type controlled the evolution, large-scale architecture, and geometry of the platform margin and slope. Lateral and temporal changes in these three parameters, and their various combinations during the Middle and early Late Triassic, were responsible for the remarkable vertical and along-strike variability in the observed platform architecture and slope profile.

Timing and rates of subsidence largely controlled along-strike variability, timing of drowning, back-step geometries, and pinnacle development. Timing of clastic basin fill dictated differences in platform-margin geometries such as slope angle, relief above basin floor, and progradation at basin margins. Shift to ramp profiles with oolite margins in the Early Triassic and back to steep-sided margins in the Middle Triassic reflects changes in carbonate-factory type following the end-Permian extinction. Eustasy, in contrast, had very little influence on platform morphology and large-scale architecture.

The evolution and large-scale architecture of carbonate platforms in south China presents an important analog for understanding, quantifying, and predicting lateral variability in seismic-scale characteristics of carbonate and mixed reservoir systems. The evaluation of controls on carbonate-platform evolution suggests that, given subsidence history, carbonate factory type, and basinal siliciclastic dispersal pattern, the basin-wide, seismic-scale evolution of carbonate accumulations is predictable. Resulting models can be used to help exploration of carbonate reservoirs in frontier or under-explored basins.

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