A Scaled Model Study of Water Coning
Authors: Khan A.R. 
Published: December 2007

The data derived from this physical model study indicate that the degree of water coning and the value of the water cut increase with production rate, with the mobility ratio across the moving boundary and across the fixed boundary, and with the ratio of aquifer to oil-sand thickness.

Introduction

When oil is produced by a partially penetrating well from a reservoir having a natural water drive, water breakthrough occurs before all of the displaceable oil is recovered. The nearness of the water-oil contact to the producing well has an important bearing on the future performance of the well. As a result of the production of fluids from the reservoir, pressure production of fluids from the reservoir, pressure gradients are established around the well that cause the water-oil contact to be raised locally. As the production continues these pressure gradients give rise production continues these pressure gradients give rise to a water cone. It may be impossible to eliminate this water in the production stream unless the rate of fluid withdrawal is reduced to uneconomical rates. If such wells in reservoirs are to be produced using their inherent water drives, it is desirable to have a method for predicting gross water movement under conditions that are both optimum and practicable. Caudle conducted a scaled laboratory model study of edge-water drive that includes a record of positions of water-oil contact as water encroaches horizontally. A similar investigation was carried out by Soengkowo on bottom-water drive reservoirs. This paper presents the results of a study, using similar techniques, on water encroachment in the vertical direction in a three-dimensional scaled laboratory model. A model was constructed to represent reservoirs with horizontal oil sand entirely underlaid by an aquifer. But in contrast with instances of bottom-water-drive reservoirs, the reservoir modeled had relatively equal, relatively thin oil- and water-sand thickness. Thus, if a well is produced from the oil zone, the upward movement of the fluids will be restricted to the close neighborhood of the well, whereas the reservoir in general will experience a horizontal movement of fluids in a radial direction. The model employed porous media and analog fluids. The water coning was recorded by operating the model under varying conditions corresponding to actual field practices. Traces of water-oil contact positions were made at different time during constant-rate positions were made at different time during constant-rate production. The traces were recorded from the time production. The traces were recorded from the time the water cone was about to break into the well or had just done so until the time the water cut had almost stabilized. For the behavior of a water cone as it builds from static water-oil contact to the stage prior to breakthrough, a correlation has been prior to breakthrough, a correlation has been presented by Sobocinski. presented by Sobocinski. Modeling Parameters

Using the techniques of scaling for oil reservoirs, dimensionless scaling groups can be designed that are suitable to come geometric and dynamic similitude between the model and the prototype. Caudle et al. have discussed such scaling parameters for application to the modeling of natural-water-drive reservoirs.

JPT

P. 771