Water InFlux

To forecast the performance in waterdrive reservoir, an aquifer model simulating the fluid flow in aquifer and that from aquifer into the reservoir is needed. Aquifer models may be classified based on flow regimes and flow geometries. In terms of flow regimes, aquifers may be grouped as pot model, steady state models, pseudo steady state models, and unsteady state models. Based on flow geometry, the aquifer-reservoir systems may be categorized as zero-dimensional,linear, and radial. The aquifer models considering radial flow geometry may additionally be sorted as edgewaterdrive or bottomwaterdrive. Aquifer models are commonly used in two different reservoir engineering applications; reserve estimate and reservoir simulation.

Water influx calculations are based on the geological and petrophysical parameters of the aquifer. Incorrect choices of aquifer parameters will result in deviation of the data from the straight line when F/E is plotted against We/E. Modifications of the aquifer parameters through a process of “aquifer fitting” can improve the match of observed pressure and production data with the reservoir characterization.

Water influx from very small aquifers can be calculated by time-independent material balance equations. However, for large reservoirs the aquifer boundary takes a finite time to respond to reservoir pressure changes and thus time dependent models such as developed by Hurst and van Everdingen, Fetkovitch, Carter and Tracy, or Allerd and Chen are used to calculate the water influx, We (Dake, 1994).

Reference : several sources

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