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Structural Analysis and 3-D Modeling of a Naturally Fractured Field in the South-East Gulf of Mexico

Abstract

Fractured carbonates represent more than 85% of hydrocarbon production in Mexico. A large number of the producing fields are located in the South Gulf Salt Province (SGSP) in Campeche Bay within the Upper Jurassic Kimmeridgian and Cretaceous carbonates. In this study, we use cores, thin sections, image logs, petrophysical models, and 3D seismic data to map fractures within a structural and stratigraphic framework. The structural interpretation of 3D depth-migrated seismic data volume reveals two structures of interest, called the “A” and “B” structures. We mapped the Upper Cretaceous, Upper Jurassic Kimmeridgian, top and base of the autochthonous salt using seismic attributes to enhance the principal faults. These maps along with vertical cross sections to represent the geometry of the two target structures provided an estimate of the age of the deformational events. Fracture analysis using cores, thin sections, well logs, and petrophysics showed the open fracture sets, being the preferential trend NE-SW. We then used this structural model and the P-wave impedance volume to propagate the petrophysical properties of the Cretaceous formation. The study area has a complex structural history and was affected by four major episodes of deformation: (1) upper Jurassic to late Cretaceous gravitational extension, forming roll-overs in structure A and salt pillows in structure B, (2) Eocene-Oligocene compression, and (3) middle Miocene-early Pliocene compression, both forming faulted detachment folds, and (4) late Miocene to Recent extension. Extension during episode 1 and compression during episodes 2 and 3 were critical to the formation of structural and stratigraphic traps within the Mesozoic fractured carbonate reservoirs; Applying integrated fracture analysis to the Cretaceous reservoirs, we found that the open fracture trends are transverse and longitudinal to the structures, and were formed due to extension during episodes 2 and 3. The transverse set of fractures has the best conductivity and is parallel to the current maximum horizontal compressive stress. The 3D petrophysical distribution indicates a good correlation between porosity, permeability, and P-impedance, enhancing the most productive fractured zones. Nelson’s classification shows the Cretaceous reservoirs to be type I and II where fractures provide the essential permeability.