Online Journal for E&P Geoscientists

Lavenu, Arthur P.^*1; Lamarche, Juliette ²; Gallois, Arnaud ²; Salardon, Roland ²; Gauthier, Bertrand ³; Pabian-Goyheneche, Cécile ¹
(1) TOTAL CSTJF, Pau, France. (2) EA 4234 Laboratoire de Géologie des Systèmes et Réservoirs Carbonatés, case 67, Université de Provence, Marseille Cedex 03, France. (3) TOTAL EP, Paris-La Défense Cedex, France.

Nearly 85 % of carbonates reservoirs are naturally fractured and over 30 % of world’s hydrocarbons reserves are located in NFR (Naturally Fractured Reservoirs) in which fracture networks controls fluid flow and/or accumulation. Implicitly, we have to consider that a reservoir is fractured until proven otherwise. To better characterize fracture patterns in subsurface reservoirs, field analogues enable to predict the geometry of reservoir’s fracture networks since they allow deciphering the nature, origin and conditions for fractures through the geodynamic history of the reservoir. We aim at characterizing true fracture patterns and determining the role of facies, diagenesis and petrophysics through geodynamic history. In this paper, we point out the impact of early diagenesis on early fractures development. Fractures patterns, sedimentary facies, diagenetic and geodynamic history have been analyzed in urgonian-type carbonates of Barremian to Aptian age of Provence, southeastern France and in lower Cretaceous to Maastrichtian age carbonates of Maiella Mountain, central Italy.

Fractures patterns are sorted based on geometrical, kinematic and diagenetic criteria from field measurements and petrographic analysis on thin-sections. Porosity types have been defined on thin-sections in order to establish the impact of early diagenesis on facies evolution. Diagenetic sequences have been determined to link fracture facies with the diagenetic history. Fractures sequences have been determined with cross-cutting relationships and compared with burial-uplift history from subsidence curves and regional structural analysis.

In both areas we observe a stage of perpendicular to bedding fracturing, synchronous with early burial and prior to major tectonic events. Fractures are joints and veins, clustered in 2 perpendicular sets, and numerous pression-solution seams. Furthermore, fractures and stylolites density is correlated to the rock porosity (high density in tight facies).

Carbonates have undergone an early diagenesis during fast and early burial, conferring early brittle behavior. The amount of pression solution seams is not correlated to burial depth but to fracture density, porosity and free air P-wave velocity. It seems that fractures development, mechanical and petrophysical properties are acquired during early diagenesis.