Water Coning and Critical Rates in Vertical and Horizontal Wells

Abstract

Producing oil at a water cut higher than necessary has always been a preoccupation for practising engineers. The existence of a critical rate above which excessive water production occurs has been mentioned earlier in Muskat's work on bottom water drive and in Dietz's paper on edge water drive. Since these pioneer studies, numerous papers have been published on critical rate. Some of these studies were based on laboratory experiments, others were based on analytical derivations; both approaches have limitations. In this study, a simple and accurate method to calculate the critical rate is presented. This method can be implemented either by numerically solving the equations of flow or by directly using a numerical simulator. The calculations are consistent with the present literature. However, there is disagreement with existing literature in at least two instances. For horizontal wells, most of the studies present the critical rate as an increasing function of the anisotropy ratio. The present study shows that this is true only for 0.5 < a < 1. In fact, for 0.01 < a < 0.1, critical rate is a strongly decreasing function of anisotropy ratio. This is not a mere theoretical case. Many reservoirs with discontinuous thin silt barriers are believed to display very low anisotropy ratios. Most of the studies describe the vertical well critical rate as a decreasing function of the anisotropy ratio, opposite in behavior to horizontal wells. Although the present study agrees with the general trend, it shows that there is in fact a harmonious continuity between vertical and horizontal wells and short horizontal wells display a behavior in between. Other results of this study present relations in dimensionless form that describe the effect of anisotropy ratio, horizontal well lengths, well penetration and reservoir geometry on critical rates.

Estimation of breakthrough time for water coning in fractured systems: Experimental study and connectionist modeling

“…Correlations developed for homogeneous reservoirs consider the effect of vertical permeability in the form of vertical permeability to horizontal permeability ratio ( K v / K h ). Presence of shale seals and compaction phenomenon lower the vertical permeability . However, there are cases such as naturally fractured reservoirs (NFRs) where the K v / K h is generally higher than one .…”

“…Presence of shale seals and compaction phenomenon lower the vertical permeability . However, there are cases such as naturally fractured reservoirs (NFRs) where the K v / K h is generally higher than one . High values of vertical permeability due to presence of fractures accelerate the water coning process that leads to reduction in the critical rate and also BT …”

“…Empirical models normally include adjustable parameters which represent a simple 1‐D system to predict the critical rate and production performance of the displacement . The dilemma here is that such correlations have been normally obtained for homogeneous porous media and are not based on comprehensive physics of fluid flow.…”

A Mathematical Predictive Tool for Determining the Time to Water Cone Breakthrough in Horizontal Wells

“…If oil production rate is above this critical value, water breakthrough occurs (Ould-amer et al, 2004). After breakthrough, the water phase may dominate the total production rate to the extent that further operation of the well becomes economically not valuable and the well must be shut down (Muskat and Wyckoff, 1935;Meyer and Garder, 1954;Chaney et al, 1956;Schols, 1972;Giger, 1989;Papatzacos et al, 1991;Suprunowicz and Butler, 1992;Guo and Lee, 1993;Menouar and Hakim, 1995;Ould-amer and Chikh, 2003;Wojtanowicz et al, 1994;Bahadori, 2010).…”

An Analytical Model for Water Coning Control Installation in Reservoir With Bottomwater

“…Finally, the well would be shut down because of the uneconomic oil production rate [Muskat and Wyckoff (1) , Kuo (8) , Høyland et al (13) , Chaperon (14) , Abass and Bass (15) , Giger (16) , Papatzacos et al (17) , Yang and Wattenbarger (18) , Yang (19) , Guo and Lee (20) , Menouar and Hakim (21) and Ould-amer et al (11) ].…”