Primary production has been carried out for more than 30 years from large overthrusted carbonate structures along the north coast of Cuba between Havana and Varadero. Long reach horizontal wells, with open hole completions, are used and extensive logging suites, including FMI, have been collected and analyzed. A huge amount of oil is held within the tight matrix but currently most of the produced oil is likely from macro and micro fractures, and breccia or vuggy porosity. It is postulated that primary production is supported by secondary gas in the fractures and "foamy oil". The EXODUS simulator has been used to model the system in dual porosity mode demonstrating the coning of gas and water in the fracture system and production from a "rim" of oil in the fractures at the level of the wells. Field observations and well performance also demonstrate the presence of gas in the fracture system and the high permeability necessary to drain the viscous oil.

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