Three-dimensional channeling flow within subsurface rock fracture networks suggested via fluid flow analysis in the yufutsu fractured oil/gas reservoir

The present study explores the fluid flows within the fractured reservoir of the Yufutsu field (Hokkaido, Japan) by using the innovative discrete fracture network models (DFN-HA model), where the critically-stressed fractures are characterized by their heterogeneous aperture distributions depending on their length and shear displacement. Simulation results suggest that the three-dimensional preferential flow paths are originally formed within the fractured reservoir (i.e., 3-D channeling flow), that is exclusively influenced by both connectivity of critically-stressed fractures and pore space connectivity within them. Additionally, the huge difference in oil/gas production between two neighboring wells (approximately 3 orders of magnitude), that is observed in the Yufutsu field, can be reproduced only by the DFN-HA models. The present study suggests that 3-D channeling flow is necessary to be considered carefully in region where the connectivity of critically-stressed fractures is extremely limited. Although it is convenient to model the fractures by pairs of parallel plates with representative aperture values in analyzing fluid flow within fracture networks, such analyses potentially lead to the wrong scenarios for developing the fractured reservoirs because 3-D channeling flow within the reservoirs is never considered (e.g., potentially overestimate the volume containing flowing fluid by more than 25%). Thus, the present study concludes that the fluid flow within fractured reservoirs should be analyzed by DFN-HA model. By continuing such approaches, we will be close to the true images and the new insights into the fluid migration within the fractured systems in Earth's upper crust.