The Zuata Field, located on the southern flank of the Eastern Venezuela Basin, produces heavy oil from porous unconsolidated sandstones of the Lower Miocene Oficina Formation. The Oficina Formation is composed of multiple depositional sequences which display complex erosional geometries. This creates an intricate reservoir architecture as younger fluvial systems down-cut, erode and re-distribute the sediments of earlier-deposited systems within each depositional sequence. Superimposed on this intra-sequence complexity is the downcutting and interconnection of sands of different depositional sequences.

The Oficina Formation within the study area can be subdivided into eleven depositional sequences. Each depositional sequence has been characterized in terms of environments of deposition and mapped, which has allowed visualization through time of the facies and reservoir geometries. Within sequences, environments of deposition include a mix of fluvial, distributary channel, estuarine, tidal channel, delta plain and coastal plain, resulting in variable net to gross ratios and variable kv/kh. Productive sands are located within incised valleys, usually within the basal part of each depositional sequence, while sediments in the inter-valley areas comprise a combination of older (pre-incision) deposits and thin delta plain / coastal plain deposits. These are variously intercalated siltstones, fine-grained sandstones and coals, and are generally non-productive.

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