Mapping the Preferential Flow Paths within a Fractured Reservoir

In a fractured reservoir, three dimensional (3-D) preferential flow paths are likely to be formed (i.e. 3-D channeling flow) due to the heterogeneous aperture distributions of individual fractures. However, to date there is no practical modeling method that precisely maps the 3-D channeling flow. In this study, we developed a novel method to analyze and predict channeling flow in an actual fractured reservoir, where a novel discrete fracture network (DFN) model simulator, GeoFlow, is used. In GeoFlow, heterogeneous aperture distributions are given for individual rock fractures depending on their scale and shear displacement under confining stress. By using GeoFlow, fluid flow is simulated for a fractured reservoir of the Yufutsu oil/gas fields, where one can observe an interesting phenomenon wherein the difference in productivity between two neighboring wells is three-orders-of-magnitude. This phenomenon can be reproduced only with the GeoFlow model, which strongly supports the idea that the three-orders-of-magnitude difference in productivity is mainly caused by the occurrence of 3-D channeling flow within the reservoir. Specifically, the impact of 3-D channeling flow on well production is expected to be significant in the domain where the degree of fracture connectivity is relatively limited. The contacting asperities within such a domain play a significant role as a resistance for 3-D preferential flow paths and, as a result, it is difficult for flow paths to be maintained consistently and there is some possibility that the flow paths vanish due to the occurrence of 3-D channeling flow. Through a series of these simulations, it is revealed that the wrong conclusions might be obtained for the development or utilization of a fractured reservoir if the occurrence of 3-D channeling flow within the reservoir is not considered.