William R. Almon1, William C. Dawson1, Sally J. Sutton2, Frank G. Ethridge2, Molly C. McCutcheon2
(1) Texaco, Inc, Houston, TX
(2) Colorado State University, Fort Collins, CO
ABSTRACT: Sequence Stratigraphy and Development of Deepwater Shale Sealing Capacity in Upper Cretaceous Lewis Shales, South-central Wyoming
The ultimate goal of this research is to develop sequence stratigraphy-based, predictive analog models for estimating seal capacity of shales and seal/flow barrier distribution for use in hydrocarbon exploration and risk analysis/mitigation. Initial research efforts concentrated on Cretaceous shales from the Denver basin. This research examines the sealing capacity of upper Cretaceous Lewis marine shales in two wells from south-central Wyoming. The sealing capacity of these shales, as determined by mercury-injection capillary pressure analysis, varies with textural and compositional variables, and sequence stratigraphic position.
Lewis Shale samples from the Champlin 276 Amoco D-1 well have significantly higher mercury injection capillary pressure values (average approximately 18,000 PSIA) and are better seals than samples from the Colorado School of Mines Lewis Strat Test No. 61 well (average approximately 3,000 PSIA). Shales from the Champlin core are interpreted as transgressive system tract deposits that include the "Asquith" marker (a condensed section). Shale deposition was dominated by suspension settling of clays, organic matter and wind-blown silt. Core from the Colorado School of Mines Lewis Strat Test are part of high frequency progradational sequences located stratigraphically well above the marker (Pyles, 2000). These sequences contain sandy lowstand systems tracts, and increased sand content in interbedded shales. Better seals have higher PSIA, total organic carbon and hydrogen index values, and lower permeabilities and percentages of detrital silt grains. Thick shales from lower frequency condensed sections and transgressive systems tracts are clearly better seals than thin shales associated with interbedded sandstones of progradational sequences.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado