Wettability effects on water mixing during waterflood oil recovery

We present experimental results of the mixing of injection water and connate water during oil production by waterflooding in two outcrop chalk samples at three different wettabilities. The displacement of connate water by the injected water was determined using nuclear tracer imaging (NTI). For all three wettabilities investigated, strongly water-wet (Iw=1.00), moderately water-wet (Iw=0.44) and less water-wet (Iw=0.28) conditions, the connate water was fully removed from the core by the injected water. The connate water accumulated in front of the injected water, and constituted a large fraction of the water that immiscibly displaced the oil from the core plug. The connate water bank was less pronounced at reduced water-wet conditions, and the mixing between connate and injected water was increased at less water-wet conditions. Connate water breakthrough was observed at one mobile-oil-pore-volume of water injected at all three wettabilities. Breakthrough of the injected water was delayed at strongly water-wet conditions compared with less water-wet conditions, where both water phases were produced simultaneously.