Play Element Prediction: Carbonate Plays in Subaqueous Evaporite Settings

L. J. (Jim) Weber and J. F. (Rick) Sarg
ExxonMobil Exploration Company, Houston, TX

Carbonate reservoirs overlain by evaporites contain about half of the known petroleum reserves. Evaporites are associated with one or more hydrocarbon systems elements (i.e., source, reservoir, or seal) in about 75% of the world's giant carbonate fields. This relationship among evaporites, carbonates, and hydrocarbons is not coincidental.

Restriction and aridity characterize evaporite basins. In these basins, carbonate source rocks are juxtaposed with carbonate reservoirs. Siliciclastic source rocks and long migration routes from basinal settings are not required for viable hydrocarbon systems. Aridity impacts carbonate reservoir quality. Shallow-water carbonate terrain that is periodically exposed is less likely to experience pervasive pore-occluding meteoric diagenesis. Better preservation of matrix porosity and permeability leads to improved storage and flow capacity of carbonate reservoirs. Carbonate reservoirs with evaporite seals commonly occur in the same supersequence.

Significant hydrocarbon reserves reside in carbonate plays associated with both platform and basin-center evaporite settings. Platform evaporites can form in both transgressive and highstand systems. Carbonate play examples include the Arab D on the eastern Arabian platform and the Osa Member in East Siberia. Basin-center evaporites are formed primarily during lowstands of relative sea level. Plays include the Madison of the Williston basin and the Keg River buildups in Western Canada.

The presence of evaporites impacts seal continuity and capacity, timing of trap formation, source potential, and reservoir occurrence and quality. An understanding of carbonate-evaporite systems provides insights into the distribution of play elements and can be used to mitigate uncertainty associated with these carbonate plays.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005