2D-IMAGING OF THE EFFECTS FROM FRACTURES ON OIL RECOVERY IN LARGER BLOCKS OF CHALK Bjorn G. Viksund1

摘要

The effect of fractures on the movement and recovery of hydrocarbons from large blocks of strongly water-wet chalk has been studied in the laboratory using 2-D nuclear tracer saturation imaging. The objectives of the experiments were to study the impact of fractures on fluid flow mechanisms, total oil recovery, distribution of residual oil and to evaluate the effect of capillary continuity across the fractures. Tracking the water flow paths in constant pressure and constant rate waterfloods on whole and then fractured chalk blocks showed that brine imbibition of the whole block occurred as a gradual uniform increase in brine saturation throughout the block with high initial water saturation, while frontal advancement of a water bank was observed with lower initial water saturation. The fractures in the blocks impeded and redirected the flow of water but total oil recovery was similar for fractured and unfractured blocks. In general, no fracture was crossed until the preceding matrix was nearly at final water saturation. Gravity segregation of fluids in open fractures was identified and had a significant impact on the flow pattern. Repeatability of the waterflood in the fractured blocks was very good.