Syn-depositional fracture network prediction in carbonates through process-based forward modelling.

Early fracture networks in carbonate reservoirs may constitute long-lasting fluid flow conduits and their characterisation is pivotal in reservoir modelling. These fractures are, however, often overlooked in reservoir characterisation due to a lack of predictive workflows. Yet, syn-depositional fracture networks significantly affect reservoir quality and performance due to (1) providing an early and effective fluid flow network, (2) are prone to reactivation during later tectonic events and (3) are pathways for early dolomitising fluids.

Understanding the processes of fracture formation is vital for predicting their spatial distribution. Syn-depositional fracture modelling is, however, challenging as they form without tectonic drivers, influenced instead by intrinsic stresses due to the internal geometries of carbonate platforms. Early lithification of carbonates further aids fracture formation due to internal weaknesses and rapid sediment progradation. In reef-rimmed platforms, fractures generally align perpendicular to the platform’s trajectory, while internal patterns vary without a predominant orientation.

Traditional Discrete Fracture Network (DFN) models are inadequate for predicting these networks, as fractures result from complex geometries rather than regional stress fields. Process-based stratigraphic modelling offers a powerful workflow to model carbonate internal geometries and their lithofacies zones, linking progradation/aggradation patterns to fracture intensity and spacing.

We developed a novel approach for syn-depositional fracture characterization, combining stratigraphic and fracture forward modelling to improve reservoir quality predictions and well placements. Outcrop analogue studies are used for ground-truthing and to validate the findings against digital outcrop models. This innovative workflow has the potential to significantly improve flow performance assessment for carbonate geothermal reservoirs.