Theoretical and experimental investigation of water in oil transverse dispersion in porous media

Document Type

Conference Proceeding

Publication Date

12-1-2008

Abstract

Water production is controlled by the size and distribution of water saturation around wells. Reported in this paper is a continuing research into mechanisms causing expansion of the water saturation transition zone (transverse dispersion) in a segregated flow of oil and water approaching a vertical well's completion. The mechanisms - including non-linear (non-Darcy) flow, turbulence, shear rate, flow baffling at grains - all contribute to instability of the oil/water interface resulting in hydrodynamic mixing. Interface instability due to shearing rate has been demonstrated in our recent study on the Hele-Shaw model. In this work, we have evaluated the practical size of the mixing zone around wells, modeled mathematically the effect of flow baffling, and demonstrated transverse dispersion experimentally using a linear physical sand pack. The maximum size of the mixing zone was evaluated using the turbulence criterion and differential velocity for typical wells' inflow conditions. Critical dimensionless numbers for flow in porous media were used to determine the onset of transverse dispersion. The radial size of mixing zones was then correlated with fluid properties, water cut, and the effective area of well's inflow. A simple model of "bifurcated flow" was developed to demonstrate the effect of two phase flow baffling in granular porous media. The model shows that the change of flow momentum of the two fluids at collisions with rock grains becomes the major factor causing water dispersion. A series of segregated (top oil; bottom water) flow runs were carried out using physical model packed with different porous media at a constant pressure drop. The runs were videotaped and analyzed for saturation distribution using a color intensity recognition software. The results clearly demonstrate onset of transverse dispersion of water into the flowing oil. Further dispersion, however, was overshadowed be the dimensional and end-point effects of the model. With a numerical estimation procedure, the initial dispersion rate - computed from the 1-D flow model - is the essential data needed to estimate total dispersion in radial inflow to wells. Copyright 2008, Society of Petroleum Engineers.

Publication Source (Journal or Book title)

Proceedings - SPE Annual Technical Conference and Exhibition

First Page

1376

Last Page

1400

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