Reservoir Characterization of the Orinoco Heavy Oil Belt: Miocene Oficina Formation, Zuata Field, Eastern Venezuela Basin

摘要

The Zuata Field, located on the southern flank of theEastern Venezuela Basin, produces heavy oil from porousunconsolidated sandstones of the Lower Miocene OficinaFormation. The Oficina Formation is composed of multipledepositional sequences which display complex erosionalgeometries. This creates an intricate reservoir architecture asyounger fluvial systems down-cut, erode and re-distribute thesediments of earlier-deposited systems within eachdepositional sequence. Superimposed on this intra-sequencecomplexity is the downcutting and interconnection of sands ofdifferent depositional sequences.The Oficina Formation within the study area can besubdivided into eleven depositional sequences. Eachdepositional sequence has been characterized in terms ofenvironments of deposition and mapped, which has allowedvisualization through time of the facies and reservoirgeometries. Within sequences, environments of depositioninclude a mix of fluvial, distributary channel, estuarine, tidalchannel, delta plain and coastal plain, resulting in variable netto gross ratios and variable kv/kh. Productive sands are locatedwithin incised valleys, usually within the basal part of eachdepositional sequence, while sediments in the inter-valleyareas comprise a combination of older (pre-incision) depositsand thin delta plain / coastal plain deposits. These arevariously intercalated siltstones, fine-grained sandstones andcoals, and are generally non-productive.