An Investigation of Early Diagenesis in from Isolated Carbonate Platform: Caicos Platform, British West Indies
Gareth D. Jones1, Edward Braun1, Roy Brown1, Glen van Gaalen1, Stephanie Gaswirth1, Walter Holzwarth1, Pamela Houser1, Alex Lee2, John Longo1, James Markello1, Glen Otten1, William Reese1, Michele Thomas1, Hsin-Yi Tseng1, and Yitian Xiao1
1ExxonMobil Upstream Research Company, Houston, TX
2ExxonMobil Corporate Strategic Research, Clinton, NJ
The diverse modern carbonate environments and island outcrops on the Caicos Platform create an excellent locale for learning the fundamental principles of carbonate reservoir characterization. This collaborative study by the 2002 ExxonMobil Predictive Diagenesis Team investigated early diagenesis at several classic Caicos field stops.
The Pleistocene age, shallowing upward parasequence, outcropping as a vertical transition from subtidal reef and shoal to beach and supratidal dune at Boat Cove, West Caicos, was sampled to describe texture, grain composition and sorting, cement, mineralogy, pore types and visual porosity. Early diagenetic products include the transformation from aragonite to partial calcite, cementation and dissolution (fabric and non fabric selective). Pore types are dominantly between particle with occasional isolated moldic pores and vugs. Measured porosity (11.1 to 33.3 %) and permeability (0.8 to 1341 mD) are significantly lower than typical depositional values. Fractures at Boat Cove are dominantly mud filled and thus would be barriers to flow. Waters were sampled from several locations including: Salinas on West Caicos, Lake Catherine, Mid Platform Shoals, Central Platform Trough and a variety of sub environments around North Caicos Tidal Flats. The presence of mesohaline to hypersaline brines suggest the potential exists for brine reflux in several Caicos environments. Numerical models of groundwater circulation, for example geothermal circulation, illustrate subsurface early diagenetic environments and processes which can not be directly observed from the platform-top.
Results from this study have been incorporated into Caicos field schools to enhance instruction of carbonate diagenesis and reservoir quality prediction.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas