Large-Scale Two-Dimensional Imaging of Wettability Effects on Fluid Movement and Oil Recovery in Fractured Chalk

The effect of embedded fractures on the movement and recovery of hydrocarbon from larger outcrop chalk blocks at different wettabilities has been measured in the laboratory. Two-dimensional (2D) nuclear tracer imaging was used to produce in situ fluid saturation distributions during oil production. Emphasis was on determining the oil recovery mechanisms by tracking the flow path of the advancing water. Two sequential waterfloods were performed on each of the three different blocks: first before fracturing, and then after fracturing. The same fracture network configuration was used for all three blocks, which were strongly water wet, moderately water wet, and near neutral wet. Waterflooding the unfractured blocks, at high initial water saturation, occurred with minimal water banking while waterflooding at low initial water saturation produced distinct water bank formation. Waterflooding of the fractured blocks showed that the "closed'' fractures produced a significant effect on fluid movement in the strongly water wet block, but only minor effect for the moderately and near neutral wet blocks. The open fracture affected flow in all the blocks. Total oil recovery was higher in the strongly water-wet block than in the moderately water wet block with the lowest oil recovery observed in the near neutral wet block.