--> ABSTRACT: Relating Fracture Patterns to Geodynamics and Petrophysics in Naturally Fractured Carbonate Reservoir Analogue (Provence, S-E France)

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Relating Fracture Patterns to Geodynamics and Petrophysics in Naturally Fractured Carbonate Reservoir Analogue (Provence, S-E France)

Lavenu, Arthur 1; Lamarche, Juliette 2; Gauthier, Bertrand D.M. 3; Guglielmi, Yves 2; Pabian-Goyheneche, Cecile 1; Ballard, Jean-François 1
(1) Total S.A, Pau, France. (2) Université de Provence, Marseille, France. (3) Total S.A, Paris, France.

About 85% of carbonates reservoirs are considered naturally fractured and over 30% of world’s hydrocarbons accumulation are located in Naturally Fractured Reservoirs (NFR), mostly in Middle East. Hence, any reservoir has to be considered fractured until proven otherwise. Field analogues enable us to predict the geometry of NFR fracture networks since they allow deciphering the nature, origin and conditions of fractures in the geodynamic history of the reservoir. Our purpose is thus to characterize true 3D fracture patterns, facies and petrophysic controls and genetic correlation with geodynamic and burial history. This will help defining calibration laws for DFN simulations.

We focused on Jurassic to Maastrichtian age carbonates of Provence. They were formed on platforms and buried in differential subsidence settings, before Pyrenean and Alpine tectonic inversions, uplift and exhumation.

We analyzed fracture patterns, facies, tectonic and burial history in nine sites: six of Urgonian, one of Tithonian and two of Campanian-Late Maastrichtian ages. Seven sites are located in poorly deformed areas away from strain partitioning and stress localization effects. Two sites are located in a fold flanks for relative dating purpose and for comparison with poorly deformed areas. Fractures patterns are classified based on geometrical, kinematical and diagenetical criteria from field measurements. Fracture sequences are determined with cross-cutting relationships and compared with burial/uplift history from subsidence curves and regional structural analysis.

Results show that fractures are clustered in two perpendicular joints sets whatever the host rock age. We observe an average spacing of 20cm and no strike neither age, facies, nor bed thickness control on fracture size. There is no mechanical stratigraphy. The fractures sequence compared to subsidence curves indicates that fractures occurred before tectonic inversion, during early and fast burial, whatever host rock age and facies.

We conclude that carbonates had early brittle properties and undergone early diagenesis. The abundance of burial stylolites does not correlate with burial depth but with fracture density, host rock porosity and P-wave velocity. We believe that porosity loss/gain and mechanical differentiation in carbonates of Provence is acquired during early burial and diagenesis which both control fracture pattern propagation.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.