Nexen Inc. is partner with Petrobras and Ecopetrol in the Guando oil field in the Boqueron Block, Upper Magdalena Valley of Colombia. The field, operated by Petrobras, has an estimated OOIP of 350 mmbbls and is currently producing more than 13,000 bopd from the Cretaceous Lower Guadalupe (Dura Member) Formation. The Lower Guadalupe Formation is ~630 ft thick. The Guando field is a westvergent subthrust play situated in the western foothills of the Eastern Cordillera. The Villeta Formation in the hanging wall overlies and seals westward dipping Guadalupe sands in the footwall of the Boqueron Fault. Source rock is the middle-late Cretaceous Villeta Formation with maximum burial and hydrocarbon generation occurring in deeper synclines. Detailed core analysis shows that the reservoir is a complex interfingering of transgressive and regressive shallow-marine deposits resulting from fluctuating relative sea levels. Field-wide bounding surfaces include wave-ravinement surfaces, tidalravinement surfaces, sequence boundaries; firm grounds revealed by the Glossifungites ichnofacies, and flooding surfaces. Highstand progradational environments include proximal and distal shelf deposits as well as distal offshore marine shales. Highstand deposits are pervasively cemented with syndepositional phosphate. Transgressive environments include tidal-inlet deposits and an estuary-complex facies association; one tidal inlet complex is dominated by micritic carbonate and oyster deposits with minor siliciclastic sandstone facies association. The best reservoirs occur in transgressive tidal inlet and incised valley facies with porosity exceeding 25 %. PSDM processing of the 3D seismic allowed recognition of basal incised valley deposits as well as tear faults. Reservoir permeability is enhanced by a complex naturally occurring fracture system.


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