The Role of Evaporites in a Holistic Investigation of Arab Sequence Stratigraphy and the Related Depositional Sequences in the Northern Part of the Eastern Province, Saudi Arabia

Karl Leyrer¹*, Franz O. Meyer², and Arndt Peterhaensel^3
1Saudi Aramco
²Carbonate Research Consulting, USA
³UP Transfer, Germany
*[email protected]

Middle East Arab reservoirs are among the most prolific in the world and their hydrocarbon-bearing intervals are well studied. The attempt to complete the understanding of the Arab Formation requires detailed analysis of the intervening non-reservoir rocks and evaporites as well. This study presents preliminary results of our investigation into the genesis and genetic relationships between Arab carbonate and anhydrite strata. It provides a detailed analysis of both types of strata and evidence for the evolution of thick anhydrite deposits through replacement processes whose initiation is intimately related to relative sea-level changes. We employed a descriptive classification for anhydrite in order to establish recurring patterns in the development of anhydrite strata and to distinguish between anhydrite of subaqueous depositional and diagenetic origin. Further analysis of relict carbonate found within anhydrite sections provided data about the composition of carbonate hosting diagenetically-emplaced anhydrite. The result of this study established that thick anhydrite intervals formed through an active consumption (Pacman-Anhydrite) of carbonate lithofacies interpreted to have a subtidal origin. Centimeter- to dm-thick polymictic carbonate breccias found in the carbonate and locally associated with anhydrite point toward anhydrite solution cumulates. Our correlation of core descriptions tied to wireline logs establishes the presence of anhydrite sections where open-marine carbonates should be. An integration of seemingly disjointed results led to the realization of a sequence stratigraphic model in which anhydrite replacement of carbonate facies is intimately related to migrating groundwater tables during sea-level lowstands. This evolving sequence stratigraphic analysis has the potential of creating a high-resolution framework for defining new exploration opportunities. Perhaps more significantly it creates a paradigm for other investigation of carbonate-evaporite couplets.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain