A Theoretical Design Procedure And Field Results For A Water-Oil Ratio Control Agent
Authors: Weaver Jimmie D. , Koch Ronney R. , Ayres Hugh J. , Shryock Stanley H. 
Published: December 2007

Introduction

Recently, a new water oil ratio control agent was introduced to the industry for field testing. Initial results of the field treatments were excellent as were previously reported. It was reported to be a low molecular weight, water soluble polymeric material, which has several advantages over the currently used conventional polymers for improving the WOR (water-oil ratio) of producing wells.

The new material has been found to exhibit improved shear degradation resistance which allows higher injection rates than can be used with most conventional polymers. polymers. The ionic content and strength of most mixing or produced water has little effect on the results of produced water has little effect on the results of a WOR treatment with this new chemical. Conventional polymers frequently form precipitates with Ca+2, polymers frequently form precipitates with Ca+2, Mg+2, etc., which may cause significant permeability damage to a formation. The viscosity yield from some conventional polymers is adversely affected by the ionic strength (salinity) of the formation water and mixing water. The effectiveness of this agent is essentially independent of ionic strength.

Many of the conventional polymers are easily oxidized by molecular oxygen so that a scavenger is normally required. This new chemical agent is not subject to oxidation by molecular oxygen.

It has been observed that clay minerals contained in a formation tend to enhance the effectiveness of this new material. Most conventional polymers are adversely affected by clay minerals. These minerals may cause a precipitation or gellation of conventional polymers which results in actual formation polymers which results in actual formation permeability reduction. permeability reduction. The new WOR agent has been found to be highly resistant to removal by produced fluids. It was expected based on laboratory experiments which indicated a strong reaction between the rock surface and the agent. Wash-off tests showed no significant reduction in effectiveness after 10,000 pore volumes of produced brine. While most conventional polymers produced brine. While most conventional polymers generate a large increase in the water phase viscosity, they generally exhibit a weak interaction with the rock surface. Such weak interaction allows a rapid removal of the polymer from the formation by the produced fluids. This new material is expected to produced fluids. This new material is expected to have a much longer treatment life than most conventional polymers because of its strong reaction with the formation. In addition, it has been found to be compatible with most strong organic and mineral acids used in oil field work.

A Possible Mechanism

Water soluble polymers generally increase the three dimensional structure present in aqueous solutions via dipole-dipole and/or charge-dipole interaction. Normally, the three dimensional structure of the solution increases as the hydrophilicity of a polymer increases. This increase in structure of the aqueous solution is revealed generally on a macro-scale as an increase in viscosity. This is one of the properties which has made many water soluble polymers properties which has made many water soluble polymers important to the oil industry as viscosifiers. The agent described in this paper is an extremely hydrophilic, water soluble polymeric material.

The WOR of a producing well can be defined as a function of the relative mobilities as shown in equation (1). It is evident by examination of this expression that holding kro, mu o and krw constant while increasing mu w will result in a proportionate decrease in WOR.

(1)

Most conventional polymers increase the viscosity of the water in the formation capillaries with limited adsorption to the capillary surfaces as indicated in Figure 1A.