Carbonate Cementation along Marine Flooding Surfaces of the Mesa Verde Group (Upper Cretaceous), Wyoming and Colorado: Implications for Sandstone Reservoir Quality Prediction

Ketzer, J. Marcelo¹, Ronald Steel², Louise Kiteley³, Claudemir Vasconcelos⁴ (1) PUCRS, Porto Alegre, Brazil (2) University of Texas, Austin, TX (3) Goolsby Brothers and Associates, Inc, Centennial, CO (4) PETROBRAS, Rio de Janeiro, Brazil

The spatial and temporal distribution of carbonate cementation in sandstones can be predicted in a sequence stratigraphic framework. Predicting the distribution of carbonate cementation is important for petroleum exploration and production because carbonate cements often play a major role in reservoir quality (porosity, permeability, reservoir compartmentalization). Detailed diagenetic study of the shallow marine and coastal sandstones of the Mesa Verde Group in Southwestern Wyoming and Northwestern Colorado (highstand and transgressive deposits of the Rock Springs, Almond, Iles and Williams Fork Formations and lowstand deposits of the Hygiene, Terry, Larimer, and Gunsight Pass sandstones) suggests that important concretionary and stratabound carbonate cementation occur associated with marine flooding surfaces. Carbonate cementation begins as microcrystalline dolomite and calcite during near-surface diagenesis owing to carbonate and Ca and Mg diffusion from seawater, which is facilitated by the prolonged residence time of sediments close to the sediment-seawater interface. Coarse mosaic dolomite and calcite textures form as cementation continues to grow during burial diagenesis, forming laterally extensive, tightly cemented zones below marine flooding surfaces. This cementation is particularly important in cases where sandstones of adjacent parasequences are amalgamated as cementation cause reservoir compartmentalization and/or baffling of fluid flow within the reservoir. The study of the distribution of tightly cemented sandstones below marine flooding surfaces in the Mesa Verde Group will help to create predictive models that can be used to anticipate pre-drilling reservoir quality in those and other shallow marine and coastal sandstone reservoirs around the world.