Deep-Water, Coarse-Grained Submarine Channels of the Valle Formation, Baja California, Mexico
Lawrence Amy, Simon A. Peachey, and Andy R. Gardiner
Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh, United Kingdom
The Late Cretaceous Valle Formation comprises over ten kilometres of deep-marine, slope-apron and submarine fan stratigraphy exposed on the Vizcaino Peninsula and Cedros Island of Baja California, Mexico. This sequence records deposition in an extensional fore-arc basin above a subduction complex and adjacent to a high-standing continental arc. The Varadero Canyon provides excellent exposures of coarse-grained, conglomeratic channels and overbank deposits. Channels are 10-30 m thick and at least several hundred metres wide. They exhibit a variety of internal heterogeneities related to conglomerate and sandstone bar forms, internal erosion surfaces and mud-rich debris flows units. Conglomerates contain clasts up to boulder size and vary from clast to matrix supported. Deposition occurred from turbulent flows, as indicated by clast imbrication, but also from debris flows as indicated by disorganised clast fabrics, inverse basal grading and rafted blocks. Overbank facies comprise thin and thick bedded sandstones and silty-mudstones. Channels have extensive conglomeratic wings, cm’s to several metres in thickness, which can extend hundred’s of metres into overbank facies away from the channel axis. In some cases, these wings connect laterally with other channels. Changes in conglomerate thicknesses associated with normal faults suggest a control on deposition by syn-depositional, extensional tectonics. In an analogous subsurface reservoir, connectivity between the main conglomerate channel bodies is likely to be good given the occurrence of sand-rich packages within the overbank and also laterally extensive channel wings. Hence, compartmentalization related to the depositional architecture is unlikely to be a reservoir issue. Future geomodelling and flow simulation work will test reservoir flow behaviour using a number of different petrophysical scenarios.
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