Reported is a study of permeability damage around a well with water coning problem - after water breakthrough, when the stratified inflow of oil (top) and water (bottom) generates a dynamic transition zone. The enlarged transition zone distributes a water saturation barrier that reduces oil inflow to the well.
Using high-resolution reservoir simulator with small grid blocks around the well, we qualified the effects of viscous force, gravity and capillary pressure, and postulated an additional effect resulting from high velocity flow around the well - transverse dispersion (i.e. hydrodynamic mixing). The effect contributes additional growth of the transition zone. Normally, in commercial simulators, the extra transition zone due to transverse dispersion would be neglected as it is overshadowed by capillary pressure when the flow velocity is low. However, it becomes progressive in the well's vicinity since the transverse dispersion coefficient is a function of velocity.
We postulate in the paper that the transverse dispersion effect should be added to the well inflow model. The proposed analytical mechanistic model employs coefficient of transverse dispersion as a function of fluid and rock properties. It is shown that well productivity could be significantly affected by water invasion due to transition zone enlargement caused by transverse dispersion. It is also shown that by diverting the stream of water with Downhole Water Sink completion the spontaneous growth of transition zone could be controlled.
After water invasion into wellbore, saturation distribution of two immiscible fluids - water and oil play an important role in well production. At first, it induces dynamic w/o transition zone and change of total mobility. These cause additional pressure drawdown when the total mobility decreases. A numerical model is built in order to verify this flow pattern and analyze how B-L model is affected by the different factors, i.e. fluids' properties, reservoir geometry and well completion. By using a commercial simulator, transition zone thickness and other two responses were selected, 6 factors were examined, 16 cases were executed to find main relations between factors and responses. The results indicated that water saturation in transition zone may affect water cut in spite of transition zone thickness.
Secondly, the growth of the dynamic water saturation around wells with oil and water two phases inflow is controlled not only by viscous forces, gravity and capillary pressure, but also by mechanical dispersion. The effect of mechanical dispersion is evaluated by saturation profile and it is a function of flow velocity and dimension of particles. It has not been included in numerical simulation because of a lack of recognition.
Understanding immiscible transverse dispersion mechanism will improve near wellbore transition zone modeling and prediction of well productivity damage due to water invasion. In this research we surveyed many associated theories and experiments. Two major factors inducing immiscible dispersion are found: shear effect and baffling effect.
A mathematical model was established to evaluate the effect of dispersion. In this model, a profile illustrating additional water saturation due to dispersion is displayed.
