The Lacustrine Carbonate Collaborative: An Analog and Process-Based Approach to Understanding Stacking Patterns and Depositional Profiles within Lacustrine Carbonate Systems
Lacustrine carbonate sediments deposited in rift settings, such as those identified in the Aptian pre-salt section of offshore Brazil, have the potential to be part of highly productive hydrocarbon systems. However, there is still much to be learned about the predictability of carbonate reservoir quality and presence, porosity development, and sequence stratigraphic concepts, as this is critical for forecasting the producibility of these reservoirs. Microbialites and coated grain grainstones have been of particular interest as important lacustrine reservoir facies, especially in light of recent pre-salt discoveries. Understanding the variability in these facies and other fundamental concepts, such as microbialite morphology, depositional profiles, parasequences, pore systems and diagenesis, will enable a more predictive capability of reservoir quality and producibility in subsurface plays.
The Lacustrine Carbonate Collaborative (LCC), has utilized an integrated approach to address such variability in lacustrine carbonate systems. Several key balanced-filled, rift system paleolake outcrops were examined: the Micoene Idaho Hot Springs Fm, Idaho USA; the Eocene Green River Fm, Wyoming USA; and the Cretaceous Yacoraite Fm in Argentina. Despite the locale and age differences, similar lithofacies associations and depositional profiles have been identified. Lithofacies include microbial boundstone (ranging from open-framework to tightly cemented bioherms with grain coatings), grainstones to mudstones with a variety of carbonate and siliciclastic components, and occasional vertisol development. These balanced-filled lithofacies stack in organized and repeated patterns at the dm to m scale. Lithofacies associations were also found to vary laterally at the km scale in predictable ways and were mapped over areas ranging from 10’s to 100’s of km2, depending on the basin.
The LCC has gained insight into the organization of
balanced-filled lake systems, employing a modular approach utilizing
paleostructure, stratigraphic and environmental controls to construct relevant
depositional models and predictive reservoir analogs. Moreover, understanding
the areal distribution and genetic organization of reservoir-prone facies, as
well as gaining insights into reservoir quality and diagenetic overprints will
allow for more predictive capabilities in potentially world-class, subsurface
lacustrine carbonate hydrocarbon systems such as the pre-salt in offshore
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California