Abstract: Application of Base-level Cycle High Resolution Sequence Stratigraphy to Correlation of Progradational Oil Beds

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