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Description:
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In South Central Cut Bank Sand Unit (SCCBSU ) of Cut Bank field , primary
production and waterflood projects have resulted in recovery of only 29 % of the
original oil in place from heterogeneous , fluvial sandstone deposits . Using highresolution
sequence stratigraphy and geostatistical analysis , I developed a geologic
model that may improve the ultimate recovery of oil from this field .
In this study , I assessed sequence stratigraphic concepts for continental settings
and extended the techniques to analyze low -accommodation alluvial systems of the Cut
Bank and Sunburst members of the lower Kootenai formation (Cretaceous ) in Cut Bank
field . Identification and delineation of five sequences and their bounding surfaces led to
a better understanding of the reservoir distribution and variability .
Recognition of stacking patterns allowed for the prediction of reservoir rock
quality . Within each systems tract , the best quality reservoir rocks are strongly
concentrated in the lowstand systems tract . Erosional events associated with falling baselevel
resulted in stacked , communicated (multistory ) reservoirs . The lowermost Cut Bank sandstone has the highest reservoir quality and is a braided stream parasequence .
Average net -to -gross ratio value (0 .6 ) is greater than in other reservoir intervals . Little
additional stratigraphically untapped oil is expected in the lowermost Cut Bank
sandstone . Over most of the SCCBSU , the Sunburst and the upper Cut Bank strata are
valley -fill complexes with interfluves that may laterally compartmentalize reservoir
sands . Basal Sunburst sand (Sunburst 1 , average net -to -gross ratio ~0 .3 ) has better
reservoir quality than other Sunburst or upper Cut Bank sands , but its reservoir quality is
significantly less than that of lower Cut Bank sand .
Geostatistical analysis provided equiprobable representations of the
heterogeneity of reservoirs . Simulated reservoir geometries resulted in an improved
description of reservoir distribution and connectivity , as well as occurrences of flow
barriers .
The models resulting from this study can be used to improve reservoir
management and well placement and to predict reservoir performance in Cut Bank field .
The technical approaches and tools from this study can be used to improve descriptions
of other oil and gas reservoirs in similar depositional systems . |