With around half the world's remaining conventional oil contained in fractured carbonate reservoirs, it is important that the fundamentals of the transfer of fluids from fracture to matrix are understood. We present the results of an extensive series of spontaneous imbibition ambient-condition experiments on three carbonate cores of different length, designed to test recent theoretical models of imbibition. We study the displacement dynamics, from an initial square-root-of-time recovery to an exponential relaxation to residual saturation as the wetting from reaches the end of the core. We also quantify the effect of pore structure in highly heterogeneous systems. The scaling models presented by Ma et al. (1995), Li and Horne (2004), and Schmid and Geiger (2012) were tested on the experimental data. Schmid and Geiger’s correlation was found to be the most reliable. The recovery, as a function of dimensionless time, could be fitted with the mass transfer function proposed by Aronofsky et al. (1958) and the analytical oil recovery solution presented by Tavassoli et al. (2005). The work suggests that recent correlations for transfer rates in the literature, combined with benchmark experimental results, can be used as a reliable technique to help predict field-scale recovery rates in fractured reservoirs.


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