Relating background fractures to diagenesis and rock physical properties in a platform–slope transect. Example of the Maiella Mountain (central Italy)

Abstract

Fractured reservoirs are of prime interest as fracture networks control most of the fluid flow and/or accumulation. However, characterizing 3D fracture patterns from subsurface data remains challenging. Studying fractures on outcrops is a good substitution to 1D data from subsurface exploration tools. In addition, outcrops allow deciphering the nature, origin and conditions for fracture formation through the geodynamic history. In this paper, we aim at characterizing the true 3D fracture patterns and determining the genetic role of facies, diagenesis and rock physical properties. We targeted a platform–slope transect within a carbonate reservoir analog, the Maiella Mountain in central Italy, where implications for analog hydrocarbon reservoir can be discussed.Fracture patterns are sorted based on geometric and kinematic criteria from field measurements and petrographic analyzes on thin-sections. Sedimentary facies, pore types and rock physical properties have been characterized in order to establish the impact of early diagenesis on rock evolution. Diagenetic sequences have been unraveled and correlated to the fractures. Fracture sequences have been determined considering the cross-cutting relationships and compared with burial–uplift history. In the two studied formations (platform and slope carbonates), we interpret a stage of fracturing perpendicular to bedding, formed at shallow depth and occurring prior to major regional tectonic events. The studied carbonates have undergone early diagenesis during fast and shallow burial, conferring early brittle behavior. The amount of stylolites is not correlated to burial depth but to fracture density, porosity and free air P–wave velocity. It means that fracture development, mechanical and petrophysical properties are acquired during early diagenesis.Both studied formations have undergone the same geodynamic history and their brittle response is different and not related to folding but to burial and early cementation. Deciphering the close relationship between sedimentary facies, diagenetic and geodynamic history has allowed unraveling the controling factors on rock properties and therefore on fracture pattern.