An Experimental Study of Smart Waterflooding on Fractured Carbonate Reservoirs

Wetting state in many fractured carbonate reservoirs exists between mixed-wet to oil-wet. Interaction of negatively charged carboxylic molecules in the crude oil with the rock surface, and high capillary pressure encountered during oil migration into the reservoir rock frequently render the rock oil-wet. Similarly, the existence of fractures solitarily governs the fluid flow dynamics in the porous media. Therefore, oil recovery from oil-wet fractured reservoirs is extremely tasking due to complex mechanisms involved in interactions between the double porosity system and the reservoir fluids. Waterflooding seems to be an economical technique to recover oil from fractured (water-wet) reservoirs where the rate of oil recovery is controlled by the water imbibition into the matrix from the fracture network. While for oil-wet reservoirs, waterflooding appears feeble and smart waterflooding looks very promising through varying of ions in the injection water. Hence changes the properties of the rock and improves waterflood performance. Middle East carbonate cores, dead crude oil, and smart water of different salinity were used in both static imbibition cells and centrifuge experiments. In order to gain better understanding of the relative contribution of oil recovery between fracture and matrix, different core configurations were used. The tests were carried out initially with formation brine and followed by different slugs of smart water. Presented in this work are the results obtained from the formation brine-oil imbibition tests and smart water-oil imbibition tests in fractured and unfractured cores. Results showed that waterflood recovery from fractured carbonate cores was about 50% of the OOIC while incremental displacement for smart water imbibition was observed nearly as high as 13%.