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Capillary imbibition and gravity are the main forces acting in fractured reservoirs. The cores used in the laboratory are usually short while experimental investigation of the gravity forces requires long samples. Therefore an experimental study has been carried out on a long core with the length of 116 cm surrounded with a simulated fracture. Kerosene and a synthetic oil with a density very close to brine have been chosen in order to distinguish the capillary and gravity effects during the water oil displacement. After doing many carefully conducted tests at different rates, it is clear that the process is significantly influenced by gravity. The second part of the study involved experiments on the long core surrounded with a simulated fracture where the flow processes are dominated by either co-current or counter-current imbibition. We changed the recovery mechanism from co-current to counter-current by changing the boundary conditions from an advancing fracture water level to an immersion-type mechanism. Our co-current and counter-current experiments on a tall block showed that counter-current imbibition has lower recovery than co-current imbibition. A wettability study was done after cutting the core into many pieces and aging the pieces in crude oil. Different wettability states were obtained by applying different aging times. The cores with different wettability index were subjected to immersion-type experiment. The results showed that more water wet conditions gave higher oil recovery.
Journal: Journal of Petroleum Science and Engineering - Volume 52, Issues 1–4, June 2006, Pages 297–304