Abstract

This paper describes the development of a comprehensive 2D near wellbore reservoir model to history match and predict the not yet fully understood production performance and deliverability of horizontal wells producing a heavy viscous oil (~300 cp). This in the presence of water conning from an active aquifer. The target application is heavy oil reservoirs (e.g. Rubiales field, Colombia) with rapidly increasing or high producing water cut (~90%), constant reservoir pressure maintained by an active aquifer, and high horizontal pay zone permeability (~15 D).

The methodology employs a simplified 2D horizontal wellbore reservoir model with enough flexibility (i.e. tuning parameters) to match the measured wells production profile (i.e. water production and producing water cut). One well with full production record was analyzed.

The following modeling strategies were tried out: providing an adequate pressure support from the aquifer, increasing artificially the oil mobility in the porous media as the water saturation increases and hindering the vertical water migration from the aquifer towards the well. These modeling strategies added additional tuning variables besides the conventional formation parameters.

Model parameters were varied automatically using an optimization engine minimizing the difference between the simulated and the measured data.

Several modeling approaches were tried out in the simulator: standalone variation of the oil viscosity, oil viscosity variation with water saturation, oil-water emulsion behavior using inversion point and Richardson model, Fetkovich type numerical aquifer, water injector with constant bottom-hole pressure and tunable injectivity index, initial water saturation variation with depth within oil zone.

Almost all the modeling approaches yielded an acceptable history match (<6%) for water production profiles. The match of the bottomhole pressure is more challenging, as satisfactory residuals are only obtained in certain production periods. It was not possible to reproduce the bottomhole pressure trend considering simple aquifer volumetric expansion and emulsion behavior throughout the entire reservoir domain.

The present paper proposes the utilization of a simplified 2D near wellbore reservoir model to successfully represent the performance of viscous oil high water cut producing wells with complex physics. The results show that it is possible to overlook the complexity of such reservoirs by "wrapping them up" in a few macro parameters and still keeping physical consistency.

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