Fractured reservoirs with fracture corridors

Outcrop studies reveal a common occurrence of tabular zones of significantly-increased fracture intensity affecting otherwise well-lithified rocks. These zones, called fracture corridors, can have a profound effect on multi-phase fluid flow in the subsurface. Using standard geo-modelling tools, it is possible to generate 3D realizations of reservoirs that contain distributions of such fracture corridors that are consistent with observations, including the vertical frequency in pseudo-wells inserted into the model at random locations. These models can generate the inputs to flow simulation. The approach adopted here is to run the flow simulations in a single-porosity representation where the flow effects of fractures are upscaled into equivalent cell-based properties, preserving a clear spatial relationship between the input geology and the resulting cellular model. The simulated reservoir performance outcomes are very similar to those seen in real oilfields: extreme variability between wells, early water breakthrough, disappointing recoveries and patchy saturation distributions. Thus, a model based on fracture corridors can provide an explanation for the observed flow performance of a suitable field. However, the use of seismics to identify fracture corridors is not an easy task. New work is needed to predict the seismic responses of fracture corridor systems to be able to judge whether it is likely that we can robustly detect and characterize these flow-significant features adequately.