Abstract: Candeias Field, Reconcavo Basin, Brazil--New Sedimentologic Interpretation of Stratigraphic Trap for Increased Production
A. V. Carozzi, J. R. Fonseca, M. B. Araujo
The Candeias field, the largest stratigraphic accumulation of hydrocarbons in the Neocomian of the Reconcavo basin, previously considered a deltaic trap, is reinterpreted as a reservoir generated by subaqueous gravity processes. The oil-producing clastic rocks in the Candeias field, investigated in 173 wells, are cyclic intercalations of conglomerates-sandstones-siltstones forming a series of isolated or coalescent lobes, oriented north-northwest-south-southeast within the lacustrine Candeias shales. General geometric characteristics and sedimentary structures are typical of turbidity-current deposits. Comparison with models of recent subaqueous fans indicates that the oil-producing clastic rocks represent deposition lobes in a mid-fan position.
Presence in the turbidites of reworked lacustrine carbonate rocks with features of subaerial exposure (caliche, desiccation) indicates that these turbidites originated from an intrabasinal shallow platform undergoing tectonic activity, and followed north-northwest-south-southeast fault-controlled channels toward the depocenter. Thick sequences of massive fine sandstones (Pitanga Member) always are located immediately behind the thin and coarse oil-producing clastic rocks, diachronically overlapping them. The Pitanga sandstone is a delta-front accumulation redeposited in complex lobes by large-scale fluidized flows prograding from north-northwest to south-southeast. Minor admixtures of lacustrine carbonate rocks indicate that the flows crossed the shallow platform along the same fault-controlled axes of transportation as the turbidites.
Development of the Candeias field itself and exploration for similar reservoirs use the fault-controlled indentation of the southern margin of the platform and/or the geometry of the large lobes of Pitanga sandstone to localize the oil-producing turbidite subaqueous fans.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC