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