Fracture Characterization of Carbonate Reservoir with Integration of Dynamic Data

Abstract

Characterization of naturally fractured reservoirs is challenging because of variable properties and high heterogeneity. One of these examples is the complex fractured carbonate reservoir of Upper Cretaceous Maastrichtian age present in a field located in onshore of Abu Dhabi.A detailed study was conducted to accurately characterize and model fracture networks occurring in the reservoir, in order to control early water breakthrough problems caused by fracture connections to aquifer and resulting in reduced oil production and bypassed oil issues.The workflow involved a full interpretation of the seismic dataset and fault networks, concluding that faults are short and discontinuous, with frequency increasing with depth.A second step included a fracture network characterization using: Core, Borehole image, 3D seismic and dynamic data. Core description showed that reservoir is dominated by short diagenetic and styloliterelated fractures, with only rare tectonic fractures. Borehole image analysis confirmed core observations and concluded that fracturing is dominated by corridors related to faults, with thicknesses of 50 to 300 ft. No small-scale diffuse fracturing was detected. Seismic attributes were combined into fracture index maps to detect large-scale fractured zones at keys levels. Good relationship was found between the faults and lineaments from seismic and large fracture clusters seen on borehole image data.Dynamic analysis using production, pressure, PLT and well test data showed that production is mainly controlled by matrix. Moderate Kh and productivity enhancement was detected at proximity with corridors (around 100 m), and water production behavior was locally explained by corridors. No evidence for small-scale fracturing flow was found.Finally, a fracture model integrating all fracture characterization results was built and allowed computing equivalent fracture properties (fracture K in x, y, z, fracture porosity and matrix block sizes), in order to optimize new well location and trajectories for increased field production and delayed water breakthrough.

Mechanical insights into the development of fracture corridors in layered rocks

“…Fracture corridors are believed to have a considerable practical impact on production in fractured reservoirs, by forming drains for fluids or providing permeability enhancement and/or anisotropy (Fig. 2a; Cosentino et al, 2001;Bockel-Rebelle et al, 2004Elrafie et al, 2008;Caetano et al, 2014). Drilling experience reveals their link to localized enhanced production (Hart et al, 2002), water breakthrough (local intrusion of water), and major drilling mud losses.…”