--> ABSTRACT: Reservoir Architecture of the Shannon Sandstone, Hartzog Draw, Wyoming, by Morgan D. Sullivan, John C. Van Wagoner, Richard W. Lovell, Mike E. Foster, Robert M. Stuart, David C. Jennette, and George Pemberton; #90906(2001)

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Morgan D. Sullivan1, John C. Van Wagoner1, Richard W. Lovell1, Mike E. Foster1, Robert M. Stuart1, David C. Jennette2, George Pemberton3

(1) ExxonMobil, Houston, TX
(2) Bureau of Economic Geology, Austin, TX
(3) University of Alberta, Edmonton, AB

ABSTRACT: Reservoir Architecture of the Shannon Sandstone, Hartzog Draw, Wyoming

Integration of core data with detailed well log correlations indicates that the elongate sandstone bodies which compose the Upper Cretaceous Shannon Sandstone at Hartzog Draw were deposited by tide-dominated deltas consisting of stacked, upward-coarsening, estuarine tidal bars. Correlation of regional stratal surfaces allows the Shannon Sandstone to be informally subdivided into 3 unconformity bounded depositional sequences: Copenhagen Blue, Crimson Red, and Canary Yellow. The Copenhagen Blue sequence boundary is a regional unconformity at the base of the Shannon Sandstone which separates distal tidal-bar deposits from offshore mudstones of the Cody Shale. The overlying Crimson Red sequence is the main reservoir interval at Hartzog Draw and is composed of high reservoir quality, proximal tidal-bar sandstones. The extremely erosional Canary Yellow sequence boundary forms the trap at Hartzog Draw by juxtaposing the reservoir sandstones of the Crimson Red sequence with the overlying offshore mudstones of the Canary Yellow sequence. The continuity of reservoir facies within these bar complexes, however, can be quite variable depending upon the lateral and vertical association of facies. In a strike orientation, lateral amalgamation of sandstone-prone, proximal bar complexes produces a relatively high degree of lateral continuity, whereas lateral amalgamation of mud-prone, distal bar complexes produces a relatively low degree of lateral continuity. Bar complexes in a dip direction display a distinct "off lapping", shingled geometry in the direction of bar accretion and a lower degree of continuity. This is due to depositional thinning, and increasing proportions of interlaminated mud and non-reservoir sandstones in a basinward (southward) direction.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado