Pressure Transient Analysis of Polymer Flooding With Coexistence of Non-Newtonian and Newtonian Fluids

Abstract

Summary Improved-oil-recovery (IOR) and enhanced-oil-recovery (EOR) methods are used to increase recovery from proven reserves, mainly after waterflooding. Monitoring and managing the progress of flood in IOR and EOR operations is currently a challenge to the oil industry, especially in situations with large well spacing and cost-prohibitive measures such as drilling observation wells (e.g., in offshore and deepwater applications). Falloff tests have proved to be successful under waterflooding operations to determine the reservoir properties in various banks around injection wells and the location of flood fronts. In this paper, we present a new development that extends transient testing and analysis technology to IOR and EOR operations during polymer flooding. With the expanded use of permanent downhole-pressure gauges (PDHGs), the newly developed technique can be used without additional testing cost or interruption of field operations. In this paper, the effects of polymer are described by shear-rate-dependent viscosity (non-Newtonian flow). We developed an analytical solution of wellbore pressure by combining the non-Newtonian fluids and the multicomposite reservoir models. The solution addresses the polymer region, where the fluids follow either the power law or Meter's model (Meter and Bird 1964), and the Newtonian flow in the oil or water regions ahead of the polymer, with varying Newtonian- and non-Newtonian-fluid saturations in both regions. The developed solution was validated by analyzing synthetic data generated using a commercial numerical reservoir simulator. In secondary-recovery operations, the Newtonian fluid ahead of the polymer bank is usually oil, and in tertiary-recovery operations, the Newtonian fluid is usually the water used in waterflooding. The solution provides a deeper understanding of the physics behind the pressure transient behaviors during polymer flooding, and can be applied to guide a better implementation of well tests. An interpretation method for falloff tests using the new solution and the conventional Bourdet derivative and Horner plots is presented, indicating that existing commercial well-testing software is sufficient to analyze data with the recent development. The new solution allows us to obtain reservoir properties such as fluid mobilities in various banks and the location of the flood front. The developed solution was applied to field data. The pressure behavior expected from the new solution was observed in the field data, validating our developed technique and yielding the characterization of reservoir parameters in various banks. Field-application results are shown in the paper. The novelty of this method of characterizing the dynamic properties of the various banks during injection of non-Newtonian fluids and the location of the flood fronts is that an analytical solution of pressure transient behavior in two-phase flow of non-Newtonian fluids and Newtonian fluids was developed, validated, and used to analyze field data. This is the first analytical solution published to address this situation.