Wettability Impacts on Oil Displacement in Large Fractured Carbonate Blocks

Abstract

Two-dimensional imaging of water and oil saturations during waterfloods in fractured carbonate rock models was obtained using nuclear tracer imaging and magnetic resonance imaging. Large outcrop chalk and limestone blocks were aged in crude oil to obtain wetting conditions from strongly water-wet to weakly oil-wet. The change in the oil recovery mechanism as the wettability shifted was investigated with and without the presence of fractures. Visualization of local, in situ fluid saturations during waterfloods improved the interpretation of the displacement process and oil recovery mechanisms. Experimental results demonstrate how fractures determine the displacement pattern differently depending on the matrix wettability conditions during waterfloods. At strongly water-wet conditions, the fractures had a minor impact on the ultimate recovery but significantly changed the progression of the water front compared to the unfractured case. At less water-wet or oil-wet conditions, capillary imbibition of water from the fracture to the matrix was reduced and fractures had a major impact on the ultimate recovery and water breakthrough time.

Experimental Study of Foam Flow in Fractured Oil-Wet Limestone for Enhanced Oil Recovery

“…The fracture surfaces, however, were not rendered waterwet, assuming that the defi nition of water-wet refers to spontaneous imbibition of water, because spontaneous imbibition of water from the fracture to the matrix during the subsequent waterfl oods was not observed. This has been experimentally confi rmed previously by high-spatial-resolution in-situ imaging using magnetic-resonance imaging on the same rock/crude-oil/brine system with similar fractures (Fernø et al 2007a;Haugen et al 2010). Microscopic changes in the wettability of the fracture surface are plausible when grains are cut and could change the fracture wettability.…”

Enhanced Oil Recovery in Fractured Reservoirs

“…Three wettability conditions were tested: strongly water-wet, weakly water-wet, and weakly oil-wet. In combination with volumetric production data, the in-situ fluid saturation data provided information about the flow pattern with the presence of fractures to better understand the recovery mechanisms (Haugen et al, 2010b). Figure 3 demonstrate the difference in waterflood behavior for three wettabilities and list the main recovery mechanisms and implications in the fractured systems.…”

Finger Thickening during Extra-Heavy Oil Waterflooding: Simulation and Interpretation Using Pore-Scale Modelling

“…For example, Haugen et al [4] studied the effect of wettability on flow in fractured rocks and used nuclear tracer imaging and magnetic resonance imaging in their study. At strongly water-wet conditions, the fractures had a minor impact on the ultimate recovery but significantly changed the progression of the water front compared to the unfractured case.…”