Oil Recovery Mechanisms in Fractured Reservoirs
All oil reservoirs are heterogeneous and the most common form for heterogeneity is fractures. Fractures often affect the oil production severely, sometimes they may improve recovery, but fractures also may severely restrict or reduce the oil production.
Main content
The objective of the research on the effects from fractures is to improve oil recovery in fractured reservoirs by establishing a better understanding of the dominant in-situ oil recovery mechanisms. The research activity emphasizes experiments imaging in-situ fluid saturation distributions during laboratory experiments of oil recovery by waterflooding large blocks of chalk, carbonate and sandstone rock at different wettability conditions and study how the fracture network impacts the recovery of oil. Numerical simulations of the experiments are performed. By obtaining information on 2D dynamic local fluid saturations, history matching of the experiments by numerical simulations will compare not only fluid production, but also the local in-situ fluid advancement.
This research activity is carried out in close collaboration with 8 universities in the US, UK, France and Norway and with 5 participating oil companies.
PhD and MS studies are available within this research activity. Contact person: Prof. Arne Graue
Experimental:
Displacement experiments are conducted in large fractured blocks of carbonate and sandstone material, with different fracture interconnectivity, where the simultaneous competition between capillary, viscous and gravity forces is studied. The local in-situ saturation information is obtained by the use of a nuclear tracer imaging technique. Introducing fractures between stacked matrix blocks gives information on the interaction between matrix blocks and the fluids in the fracture network. The relative importance between viscous and capillary displacements is studied. The blocks are mounted vertically and waterflooded first as a whole block, then after fracturing and reassembling, waterflooded with fractures.
To establish relevant conditions for the reservoir with respect to rock properties, spontaneous imbibition characteristics and wettability conditions, predictable and reproducible restored state conditions need to be obtained. We have recently published a series of papers describing how reproducible alteration of wettability in chalk may be obtained. In a series of papers recently published we have shown how fractures impact fluid flow under different wettability conditions. Further work will continue this study, with interconnected fracture networks in carbonate rock and in sandstone. Tilted fractures and variation of parameters such as flow rates, i.e. differential pressure, stress across fractures etc. will be performed. All experiments will be simulated using full field simulators for fractured reservoirs.
The large block experiments will be assisted by complimentary, high resolution MRI tomography of fluid flow across fractures and fluid exchange between fractures and rock matrix. This has been successfully imaged for fluid flow in fractured chalk. Further mechanistic work will be carried out in fractured chalk and in strongly-water-wet sandstone and carbonates. Depending on successful alteration of wettability in carbonates and sandstones similar experiments are planned at various wettability conditions. Alternatively, if reservoir rock is provided from a field with less-water-wet conditions experiments may be carried out at relevant reservoir wettabilities. Emphasize will be on controlling the wettabilities as this parameter is of utmost importance when considering the mechanisms for fluid exchange between fractures and matrix.
