Leila Jalali Dil - No.۷۳۵, ۷th floor, Petroleum Ministry of Iran, Taleghani Str., Tehran, Iran

One of the basic reservoir models for naturally fractured reservoirs is Conventional Warren and Root model in which matrix are defined as small cube blocks and fractures are narrow perpendicular blocks surrounding the matrix. This model can be applied for both dual porosity (DP) and dual-porosity/dual-permeability (DPDP) reservoir models. In DP models, well can only be completed in fractures and there is no flow from matrix to wells. While this problem is solved in DPDP model, it is both more considerably complex in calculations and time consuming. Also, in case of high production flow velocity, DPDP model will be unstable. This paper is to produce a model based on Warren and Root which not only has the capability of simulating simultaneous flow from both matrix and fractures toward wells, but it also is simpler than DPDP model regarding its easier calculations and shorter simulation time.This model is called DCWFM model and includes a new non-reservoir layer on top of reservoir ones which contains new wellhead location. This layer must be gridded in such a way that the new wellhead block would cover all of well, matrix and fracture blocks connected to the well in lower reservoir layer.Deactivating all blocks except wellhead one in this layer resulted in restriction of fluid flow between reservoir and upper non-reservoir layer to wellhead flow. Wellhead plays a role similar to halo cell in this model. In this way, while majority of fluid flow is still from fractures, the error of ignoring flow from matrix blocks is decreased by defining direct connection between wellhead and matrix. In addition, this model can simulate a reservoir in which fracture density near well is completely different from other reservoir sections by using Local Grid Refinement (LGR) in matrix blocks next to the wells. It must be mentioned that DP model cannot simulate high heterogeneous reservoirs and DPDP model must be used in these cases. Using DCWFM model not only solves this problem, but it also makes it possible to connect new fractures directly to the well.At the end, a comparison is done between results of an experimental study of polymer gel injection (as a shut-off method) in an Iranian carbonate oil reservoir with simulation results of both polymer gel injection in DP model and DCWFM model. Changes in relative water and oil permeabilities before and after gel injection are considered as basics of comparison. Although both simulation models show significant decline in water relative permeability after gel injection, the overall trend of changes in new model matches more perfectly with experimental results which is a confirmation of error decrease in this model with respect to DP model. In the case of relative oilpermeability, fewer differences can be seen between two simulation models. This is due to the fact that targets of polymer gel injection are law-permeable layers which contain fewer fractures. Therefore, type of connection of wells and fractures (direct or indirect) does not have significant effect on production and relative permeability. Finally, it can be say that in cases of heterogeneous reservoirs with variety of fracture densities, this paper presented a new model which is simpler than DPDP model and more accurate compared to DP model.

Naturally fractured reservoirs, connection between well with fracture and matrix, reservoir simulation, wellhead definition