Seismic Sedimentology of Complex Non-Marine Depositional Systems in Cretaceous Qingshankou Formation, Qijia Area, Songliao Basin, China

Songliao Basin has been the largest hydrocarbon producer in China for more than four decades. Entering a matured and advanced exploration stage, geoscientists are increasingly focused on targeting thin (1-10m) and stratigraphic traps for reserve growth. Prediction of these subtle reservoirs with available 3D seismic data and limited well control are challenging, though, which is evidenced in Qingshankou Formation by the fact that multiple lithology types (sandstone, calcareous sandstone, shale, and limestone/marl) coexist in formation, and complex and ambiguous seismic geomorphologic patterns that are quite different from those in marine sediments and difficult to interpret.

This study was aimed at integrating seismic lithology and seismic geomorphology for improved reservoir prediction. A new workflow was employed, which includes such key steps as 90° phasing of wavelet, establishing seismic chronostratigraphic framework, frequency adjustment, petrophysical analysis, attribute analysis, stratal slicing, and seismic sedimentologic mapping by integrating core description, wireline log facies and stratal slices. Two key research issues are (1) how to recognize relevant seismic signal for identifying the best reservoir among different lithology types, and (2) how to optimize seismic attributes and visualization methods to map depositional systems at high resolution and thin-bed level.

We recognized 8 high-order sequences in 300-350 m thick Qingshankou Formation. Each sequence is composed of a LST at bottom and a HST at top, which are basic mapping units for the study. Core and wireline log analysis revealed fluvial-dominated deltaic facies, including distributary channel, mouth bar, delta-front sand sheet, prodelta, and lake. Vertical stack of alternative LSTs and HSTs explains certain lithology/impedance/amplitude associations for different systems tracts. Channel forms, relative impedance (as an indicator of diagenetic facies and reservoir quality), and fine-scale facies boundaries were interpreted from different attribute displays and were superimposed for comprehensive facies interpretation. In some favorable cases, sandstones as thin as 1 m were predicted with the process.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California