New upgridding method to capture the dynamic performance of the fine scale heterogeneous reservoir

Many tight gas reservoirs are characterized by large gross interval with significant presence of shale and interspersed sand. The geo-cellular models of these reservoirs, which honor the resolution of log data, contain large number of layers. Without significant upgridding of vertical layers, flow simulation of such reservoirs is very difficult. Ideally, the upgridding process should be conducted such that the dynamic performance of geo-cellular model is preserved in the upgridded model. One way to ensure efficient upgridding is to preserve fine scale pressure profile in the coarse scale model. s study we observed that, in heterogeneous reservoirs, the vertical communication across layers has a big impact on the flow behavior in a fine scale model. In the presence of vertical communication, fine scale heterogeneities are homogenized. That is, layers with different permeabilities have similar pressure profiles during the depletion phase. Hence by combining these layers into a single layer would still predict a similar dynamic performance. In contrast, when crossflow across layers does not exist, combining those layers would result in much different dynamic behavior than fine scale behavior. It was observed that upgridding performance is not only influenced by the extent of sand connectivity across the layers (which tells us about vertical communication) but also how areally dispersed the connections are present. In the case of existence of dispersed shale within reservoir it was found that the vertical flow is more helped by smaller sized vertical connections between layers, which are areally dispersed, than large sized connections concentrated within a certain region. Analytical solution is provided to quantitatively prove the effect of size as well as dispersed nature of connection across the layers. Using the underpinnings of analytical solution, a new methodology is developed which combines layers based on sand connectivity (vertical permeability) across adjacent layers as well as their respective petrophysical properties (horizontal permeability). proach is analytical. However, it was shown that the analytical upgridding error we estimate closely mirrors the simulation error which represents the difference in the dynamic performance of fine versus coarse layers. We validate our method by applying it to both synthetic as well as field cases. Through these examples, we demonstrate that newly proposed method is superior to proportional as well as variance and flux based upgridding methods.