Abstract

Today several methods are being investigated to control production of water in oil wells. Recently it has been shown that the polymer treatment of producing wells can reduce water-oil ratios dramatically. A numerical coning simulation study has been conducted to investigate the effect of injecting polymers in oil wells. This study supports the position that the polymer treatment of oil wells can retard water coning time.

The simulation approach provides the means for quantifying the incremental gain in oil production after polymer treatment. This information coupled with an appropriate economic analysis provides the engineer with a method for determining the feasibility of polymer injection in oil reservoirs.

Introduction

Several papers have been published to show the effect of polymer injection in oil wells which also produce water. Kruger (2) described how ultimate recovery from a reservoir was increased by polymer workover. In one case a well which produced 100 percent water recovered an additional 12,000 bbls of oil with a water-oil ratio less than 10 after the polymer treatment.

Recently, White et al (1) reported that a decrease in water-oil ratio of approximately 60 to 90 percent was achieved by the use of polymer injection in 200 wells studied. Based upon experimental studies, they concluded that residual polymer reduced the relative permeability to brine as much as 77 percent whereas the relative permeability to oil was only reduced by six percent.

Other investigators (4,5,6) have noticed a several fold reduction in water relative permeability with little effect on oil relative permeability due to polymer solution injection. Sandiford and Graham (3) also mentioned the injection of polymer solution in producing wells reduced water production.

When solutions of partially hydrolyzed polyacrylamide are prepared, their properties largely depend upon the solvent. The molecules of partially hydrolyzed polyacrylamide are hydrophilic in nature and thus have a strong affinity for water. If a polymer molecule or unit is present in a capillary channel, as in a porous medium, it reduces the water mobility drastically, because in contact with water or brine, they are uncoiled. However, if present in a pore channel where predominantly oil is flowing, polymer molecules shrink due to a low affinity for oil. The above described properties of these polymers make them attractivefor field use where water coning is a problem.

Sandiford and Graham (3) suggest that a reduction in water permeability and thus the water production would cause a drop in the fluid level of a well. This in turn will increase the pressure drop from the reservoir into the wellbore. The oil production will increase with the increase in the pressure drop.

The efficiency of reduction in water permeability is also dictated by the degree of hydrolysis in the case of partially hydrolyzed polyacrylamide. Burcik and Walrond (8) have observed that the resistance effect of a polymer solution is enhanced with the increase in the degree of hydrolysis of the polymer tested. Similar observations were also made by Sandiford and Graham (3).

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