Use of Polymers To Control Water Production in Oil Wells

Abstract

Although in nearly 200 field treatments of producing oil wells polymers have effectively reduced the WOR, not all such wells polymers have effectively reduced the WOR, not all such wells with a high water cut are candidates for polymer treatment. This paper discusses the probable working mechanisms of polymers and presents guidelines for selecting wells to be treated. Introduction The use of polymers to reduce water production in high-watercut oil-producing wells has proved highly successful in many areas of the Mid-Continent region. This process is an outgrowth of the use of polymers to adjust permeability profiles for water polymers to adjust permeability profiles for water injection wells. It has been used in nearly 200 wells to date and has resulted in a water-oil-ratio (WOR) decrease of 60 to 90 percent in most wells. In many cases, oil production has been substantially increased. The flow of polymer solutions through porous media has been a subject of intense research over the past decade. A thorough review of this subject has been given by Savins and therefore will not be repeated here. Polymers are of interest to the petroleum industry because they are useful in secondary petroleum industry because they are useful in secondary recovery and in the improvement of injection profiles in waterflooding. The behavior of polymer solutions in porous media has been controversial and several mechanisms have been proposed as an explanation of polymer behavior. Perhaps more than one mechanism is operative, depending on conditions. We believe that the basic behavior of the polymers is independent of the process, but the techniques of using polymers and the way they are applied in different processes do vary. The treatment of producing wells with polymer solutions is a unique process to reduce the WOR by selectively reducing water production without greatly hindering oil flow. As the polymer solution is injected into the formation, it tends to seek out and flow into the higher-permeability water zone. For this reason, deeper penetration is obtained with the polymer than is possible with conventional nonselective plugging agents. For producing wells, when the treatment is successful, the response is usually rapid and dramatic and occurs in a matter of days. In contrast, with water injection wells and polymer flooding, the results of a polymer treatment may not be evident for 6 to 12 months or even longer. How Polymers Work Before discussing the details of how polymers work, we shall outline the salient features of this process. This paper is aimed at those persons unfamiliar with the process and is not intended to be technically precise. The terms "resistance factor" and "residual precise. The terms "resistance factor" and "residual resistance factor" have been defined elsewhere. Although these terms are applicable as defined, we also use them in a general sense, as shown in the following discussion and in Fig, 1. Because of its viscosity, a polymer solution would be expected to offer a given resistance to flow in a rock. The actual or total resistance to flow offered by some polymers, however, is some 5 to 20 times this expected resistance. The total resistance is important in polymer floods and injection wells, but is effective in producing wells only until the solution is returned producing wells only until the solution is returned to the wellbore. Core tests show, however, that after a polymer treatment, even after hundreds of pore volumes of brine have been produced, enough polymer is retained in the rock to provide a residual resistance that will reduce the brine flow by as much as 60 to 95 percent. JPT P. 143