Sedimentology and depositional model for the Early Miocene Oficina Formation in the Petrocedeño Field (Orinoco heavy-oil belt, Venezuela)

摘要: Abstract The Early Miocene Oficina Formation in the Petrocedeno Field (Venezuela) produces extra-heavy oil with an initial gravity of 8.5° API. Reservoir zonation is successfully based on a 3rd-order sequence stratigraphic framework for which detailed sedimentological understanding crucial. This paper presents a, primarily core-based, account sedimentology and stratigraphy Junin (formerly Zuata) Region Orinoco heavy-oil belt. In Petrocedeno, typified by long-term (approximately 7 Ma; 2nd-order sequence) change fluvial dominated deltaic system to tide-dominated lower delta plain subsequently tide-dominated, subtidal, upper platform. A braidplain environment mostly sand-dominated braided sinuous rivers (Sequences 1 2) changed into fluvially-dominated but notably tidally-influenced straight channel belts 3–6). Subsequently, mixed-energy (fluvial tidal) front numerous distributaries formed. drowned estuary bay-head mouth bars (Sequence 7). Maximum transgression was reached Sequence 8 development fully marine shale. low-gradient meandering established 9 10). These were gradually transgressed develop proximal platform environments limited number distal large protected subtidal areas 11). Together, facies form one few currently known subsurface examples delta. depositional style controlled increase accommodation space developing Eastern Venezuelan Basin. part formation compressional tectonic activity (third-order Sequences through 6). half, however, eustatic changes