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

Abstract

Abstract 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. Introduction Petrozuata Petrozuata, S.A. is a joint venture company with Conoco (50.1%) and Petróleos de Venezuela, S.A. (49.9%). Built from the ground-up in less than three years, Petrozuata has drilled 306 horizontal laterals and 145 vertical wells and is currently producing approximately 120,000 bbls oil per day. Each of the horizontal wells is custom designed and then "geo-steered" during drilling to access the reservoir in the most efficient manner. Petrozuata produces extra-heavy crude oil (9 to 10 API) from the Zuata Region of the Faja Petrol fera del Orinoco (the Orinoco Oil Belt). The heavy oil is diluted with naphtha to yield a 15–17 API blend, which is transported via a 200 km pipeline to the north coast of Venezuela. There, a delayed coking-based upgrader facility converts the diluted crude to synthetic crude oil, along with associated by products of LPG, sulfur, petroleum coke and heavy gas oil. With over 20 billion bbls of oil in place, the Petrozuata joint venture has a 35-year operating life. This will require the drilling of up to 750 horizontal wells to ultimately recover 2 billion barrels of extra-heavy crude. Location and Geological Setting The Faja (Orinoco Oil Belt) is located on the southern flank of the Eastern Venezuela Basin (Fig. 1), and contains about 1.2 trillion bbls of in-place oil, stratigraphically trapped in Miocene-age fluvial- and marginal-marine reservoirs. PDVSA has subdivided the Orinoco Oil Belt into four areas (Machete, Zuata, Hamaca and Cerro Negro). Petrozuata is currently developing part of the Zuata area.