Sorrento Field, southeastern Colorado, contains an estimated 21 million barrels of original oil in place in the Pennsylvanian Morrow sandstone. The reservoir consists of a complex of stacked channel sequences within an incised valley. Interpretation of 3-D compressional seismic data has outlined the configuration of the incised valley and provided essential information about the characteristics of the rocks that fill it. This seismic interpretation provides stratigraphic details on the compartmentalization of the four flow units which explain the multiple fluid contacts and variable performance of wells in this field.
The petroleum industry has been challenged to characterize
Morrow reservoirs because the sandstone reservoir is encased in
marine mudstone; normal compressional seismic data are not capable
of imaging reservoir rock because the acoustic impedance is not
sufficient to distinguish the two lithologies. Rather, seismic
modeling shows that the compressional seismic character of the
Morrow interval is primarily due to high velocity/high density
non-reservoir rocks. The distribution of these non-reservoir rocks
is critical in delineating the reservoir because the channel sandstone
is bordered by reflective rocks such as floodplain deposits or
high density facies which lie outside of the valley wall. Non-reservoir
rocks which are barriers to flow within the reservoir, such as
carbonate-cemented zones, define the compartmentalization.