Reduction Of Water-Oil Ratio Using Polyacrylamides In Vugular Carbonate Reservoirs
Authors: Legere R.F. 
Published: March 2010

Abstract
The use of partially hydroiyzed polyacrylamides to control water production in oil wells has been attempted in various areas of North America over the past ten years. This use has met with various amounts of success. It is felt that a careful evaluation of past treatment techniques and materials compared to well response can provide valuable data applicable to future treatment design.
The purpose of this paper is to review and evaluate past treatments and show how the information developed has been used to design specific treatments. The results of these treatments, in turn, are evaluated in an attempt to establish guidelines for engineering future treatment designs to achieve a higher success ratio.

Introduction
Many oil wells produce throughout their lives without serious problems arising from undesirable fluid movement. The producing zones in these wells appear to have reasonably uniform permeability distribution, with a horizontal permeability much greater than the vertical permeability.
Other formations have poor effective permeability, which can create problems during the producing life of a well. Fluid flow through 'such formations will occur in the zones of highest permeability. As the effective vertical permeability approaches the effective horizontal permeability, cross flow or vertical movement of water can cause coning.
The petroleum industry has long recognized the need for a material to control the unwanted movement of water into producing wells. The task of providing such a material has been difficult due to wide variations in well and reservoir conditions. It has been further complicated by the very manner in which the permeability exists. The permeability of a rock formation may exist as matrix permeability, as hairline fracture permeability or as a result of connecting vugs or large pores in the rock. Artificial permeability, such as hydraulically induced fractures, can create unequal permeability distribution.
Because of the wide variations in well and reservoir conditions, many materials and techniques have been used to reduce water production in oil wells. Because the problems of matrix sealing and fluid diversion within a formation are 50- complex, no single material can be expected to solve them all.

Water Shut-Off Techniques
Many materials and techniques have, been proposed to reduce water production in producing oil wells. Some of these are:Cement Plugs(1–5)Diesel Oil-Cement Squeezes(6–8)Emulsion Plugging(9)In-situ Polymerization AgentsPolymeric Water Gels(10–12)Polyisocyanurate Salts(13,14)Furfuryl Alcohol Resins(15)Lignosulphate Gels(16,17)Silica Gels(18,20)Polymers(20–28)Biopolymers(20–28)Polyelectrolytes(29)Polyacrylamides(30–58)
Each of the above materials or techniques has shown some degree of promise. However, each 'has a limited application, because it is suitable only to a particular set of well or reservoir conditions. Of all these materials, the polyacrylamide polymers probably have the widest application for controlling water production from producing oil wells.
Considerable controversy still exists as to the mechanisms by which these polymers -function to reduce water production