Pre-Salt Lacustrine Coquinas Limestone Reservoir of Lower Cretaceous Itapema Formation in Santos Basin, Brazil

Abstract

Thick packages (300–400 m) of coquina are hosted by several Brazilian and West African continental margin basins, having been deposited on shallow lacustrine platforms created during the break-up of Western Gondwana in the Early Cretaceous. Coquina reservoirs are known from the Santos basins, where they are associated with combination structural–stratigraphic traps (also having a diagenetic component), and produce oil with an API ranging from 28–33°. Coquina reservoirs produce 1000–3000 barrels of oil per day and can have initial flow rates of N10,000 bopd. Coquina exhibits profound lateral and vertical changes in reservoir thickness and quality over short distances in response to diagenetic alteration, and biologic, topographic and climatic controls that restrict their distribution. Coquinas exhibit similarities in depositional processes across the South Atlantic, however, have distinct diagenetic histories and stratigraphic stacking patterns, having been deposited in lakes with different geologies, climates and water chemistries. Coquinas limestones of L block, Santos basin deposited on low angle ramps. As petroleum exploration continues into ultradeepwaters on the Brazilian andWest African margins, accurate facies modelswill be important for the predictability of carbonate reservoir intervals. Parameters controlling the development and distribution of coquina facies in rift-lake settings are complex: these factors include, but are not limited to, climate, water chemistry, basin architecture/platform morphology, catchment geology and siliciclastic sediment influx. All these factors affect molluscan productivity and have intricate associations with one another. For example, lake chemistry is strongly influenced by lake hydrology, which is in turn regulated by fluctuations in climate and evolving tectonic regimes, factors that are also responsible for the delivery of siliciclastic sediments to the basin. Other factors includewater circulation patterns, larval dispersal capabilities and environmental tolerances etc. In addition, post-mortemmodification processes and sediment bypassing are important for the subsequent preservation and concentration of shell-rich facies. Another potentially important factor to consider with respect to coquina development is the impact of marine incursions, which has not been considered as substantial in the past.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016