Predicting the movement of fluids in large naturally-fractured carbonate reservoirs is challenging because of the many uncertainties such as complicated fracture networks and the heterogeneity of carbonate rock; however, flow models are necessary to understand and predict reservoir behavior. In this paper, we study one such reservoir where there are concerns with the potential for very high water production.

A well from this reservoir was suspended due to water cut (up to 60%) shortly after putting it on production, and there is concern that the water seen at the well might end up at nearby wells. The objective of dynamic analysis is to predict potential water flow from the aquifer through the fractures to two other producing wells.

A three well section of this reservoir is studied by combining a discrete fracture network (DFN) model with a finite difference flow simulator. Fracture parameters such as intensity, size, shape, and orientation are assigned to each fracture based on measured data or relevant statistical distribution derived from the measured data. Well test results, using the constructed DFN models and the results of actual test, are used to determine skin and fracture permeability. The DFN model is then upscaled to obtain grid properties including porosity, permeability and sigma factor suitable for a dual porosity flow simulation model.

Many different scenarios are simulated with different water influx rates and different DFN models, which show the wide range of water breakthrough times (16 to 161 months) and cumulative produced water volumes (8,000 to 1,000,000 bbl), however the largest impact on the results is the aquifer strength. We recommend further testing the shut-in well to try to estimate the influx potential, so a more accurate prediction can be made for breakthrough time and produced water volumes.

The workflow presented in this paper allows for building representative models of fracture networks, which can improve reservoir characterization, flow predictions and reservoir management strategies.

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