Abstract: Application of Base-level Cycle High Resolution Sequence
Stratigraphy to Correlation of Progradational Oil Beds
RENHAI, PU
Many reservoirs in
East China form in the sandbodies of progradational subaqueous fans or
deltas. One example is the proximal turbidite fan reservoir of Zhuang 52,
Shengli Oilfield. Because of low angle (less than or equal to 13 degrees)
and thin thickness (50 m plus or minus ) of the foresets, there is generally
no obvious pragradational reflection on seismic profiles. Thus total four
oil beds were divided throughout the reservoir before, and different facies
tracts were often grouped into the same oil bed. Despite close well
spacing
(300 m plus or minus) and as long as ten years' development, recovery is
only about 25% with a nearly 90% water cut.
After the research on base-level
cycle high resolution sequence
stratigraphy incorporated with 3-D seismic
interpretation, it is found that the reservoir turns out to be composed
of 20 progrational lobes of turbidite sandbodies. A progradational lobe
corresponds to a base-level cycle. At each
well
spot there are normally
four base-level cycles. The top and bottom of the reservoir (also the
log
reference demarcation lines) systematically and regularly cross the upper
reflection events northward on the
well
-linked 3-D seismic profiles, suggesting
the existence of progradation. Horizontally different parts of each progradational
lobe has variable cyclicities and heterogeneities.
This method of correlating progradational oil beds extremely improves the water injection response, and constructs an exact and reliable static geologic model for defining residual oil distribution and enhancing recovery efficiency.
AAPG Search and Discovery Article #90940©1997 AAPG Foundation Grants-in-Aid