Polymer flooding is the most commonly applied chemical enhanced-oil-recovery technique. This paper provides an update on the status of polymer-flooding technology, focusing more on field applications than on theoretical and laboratory research. It covers the following topics: • Mechanisms of polymer flooding • Polymers used • Polymer-solution stability • Technical screening criteria • Laboratory and simulation work • Performance-monitoring technique • Summary of pilots and large-scale applications • Experience and learning from field projects • Polymer flooding in heavy-oil reservoirs • Polymer viscoelastic properties • Problems associated with polymer flooding and their solutions • Future developments The data and analysis presented in this paper will give readers updated information describing polymer flooding, as well as a guide to the relevant research. Survey data will also provide operators with reference data for project design and optimization.

Dimethyl Ether Enhanced Waterflood (DEW) is a novel and promising solvent-based EOR technology developed by Shell. Dimethyl Ether (DME) is a widely-used industrial chemical which is applied as a water soluble solvent for EOR applications to enhance a conventional waterflood. Once the DME-brine solution is injected into the reservoir and comes in contact with the oil, the DME molecules partition into the oil phase which leads to oil swelling and mobilization of residual oil. Moreover the partitioning of the DME into the oil phase decreases the oil viscosity and improves its mobility. The combination of these effects results in both a significantly higher ultimate oil recovery compared to the conventional waterflood as well as accelerated oil production at lower energy footprint compared to thermal technologies. As the solvent is water soluble, it can be very effectively back-recovered from the reservoir by re-dissolving the trapped DME in the DME-free chase water slug. The solvent is recovered from the produced oil and water streams at surface and re-used. The main objectives of this paper are to present the first experimental results, explain the physical mechanisms of this novel concept and demonstrate the extra oil recovery. Additionally, modeling workflows used to interpret the experiments and predict the benefits of field EOR application are illustrated.To gain an insight into physical mechanisms behind the DEW, develop modeling workflows and de-risk the technology, an extensive experimental program was set up to investigate both the fluid-fluid and rock-fluid interactions. Phase behavior of DME/brine and DME/crude mixtures has been carried out, with a focus on the partitioning of the solvent between brine and crude. Mixing rules for properties affecting the phase mobilities have been determined. In parallel, a number of coreflood experiments were conducted on both carbonate and clastic cores of varying permeability to investigate the dynamic DME/crude behavior and DME/rock interaction. PVT experiments were used to build phase equilibrium models. Based on these PVT models, the coreflood experimental data was matched and interpreted using numerical simulation.Coreflood experiments confirmed the phase behavior-driven character of the DEW technology. A good match between the experimental and simulated oil recovery was obtained in most cases. This shows that PVT models, generated using measured basic data, are in a good agreement with the dynamic coreflood experiments.

Implementing Enhance Oil Recovery techniques in heavy oil reservoirs with strong bottom water drive has been a challenge in the oil industry. This paper describes an Enhanced Oil Recovery process in which polymer is injected into a clastic reservoir with a strong bottom aquifer drive bearing heavy-oil (250-500 cP). The high reservoir permeability (2-5 Darcy) enables stretching the viscosity limit of a standard polymer application. The presence of a strong bottom aquifer maintains high reservoir pressure, which could provide a challenge to injectivity. The close proximity of injectors to the oil water contact reduces the efficiency of the polymer flood through water fingering, and polymer loss to the aquifer. To best understand details of the influence of aquifer on the recovery process, test different development scenarios and address key uncertainties, detailed simulation study was conducted. The simulation results showed that the optimum development concept which would help reduce impact of polymer loss to the aquifer would be to utilize the currently existing and future horizontal producers, augmented with additional infill horizontal injectors placed approximately mid-way in the oil column. Optimization of the development was performed using the simulation model where the polymer viscosity, slug size, and injector location were optimized for net present value. Uncertainty analysis using the simulation model showed that factors such as poor injectivity, poor conformance control and high kv/kh ratio have negative impact on process efficiency. To address and mitigate these key risks and uncertainties a number of activities are underway. These activities include intensive laboratory tests, field injectivity test and a field trial where polymer is injected in newly drilled injectors. The paper discusses study to identify the optimum development concept, key uncertainties and associated risk reduction activities. Finally, this paper discusses the design and the surveillance aspects of the upcoming field trial.

This paper describes the search for viable EOR techniques for a medium-heavy oil reservoir with high permeability and a strong bottom aquifer in south Oman. Horizontal production wells drilled at the top of the oil column yield high (commercial) initial oil rates however, they suffer fast water breakthrough and subsequent oil production is at high water cut. Given the poor primary oil recovery, these reservoirs are candidates for EOR as a means by which to improve the ultimate recovery. However, determination of the most appropriate process is non-trivial as field characteristics pose a significant challenge to most EOR schemes. These challenging characteristics include an oil column of around 40m, a large and strong bottom aquifer, sustained high reservoir pressure (100bar) and medium-high oil viscosity (250 to 500cP).Three EOR techniques were identified as potentially feasible, both in terms of increasing ultimate recovery and their practical implementation; in-situ combustion (ISC), high-pressure steam injection (HPSI) and polymer flooding. None of the three processes are conventionally prescribed for reservoirs such as these and modifications to the basic processes were imperative. ISC is generally applied to thin, confined and dipping sands in the absence of bottom water. Steam injection is normally applied at low reservoir pressure and polymer is normally applied to oils with viscosity less than 150cP.The paper describes a fully integrated evaluation of these EOR processes. Comparison is made in terms of simulated incremental recovery, economics, energy requirements and CO2 footprint, target volume and the practicality of implementation in a brown field. Against these metrics, polymer flooding is shown to be the best option.

This paper covers EOR development concept screening from a sub-surface perspective. The field in question is a medium sized heavy oil field with complex geology that is located in South Oman. The two front running concepts considered are steam and polymer flood, both of which present their own challenges. Common to both concepts are the difficulty in obtaining adequate conformance in a field that is characterised by high and highly variable permeabilities in a channelised environment and that includes lateral extensive shales that break the system up into vertically distinct sand units. Additional challenges are presented by a permeable regional scale aquifer, an erosive top surface that reduces the equivalent oil column (EOC) in the core of the field leaving thicker columns laterally close to the edge aquifer and the friable nature of the sand that makes sand control necessary. Challenges specific to steam are the relatively high initial pressure, inferred connection to a regional-scale strong aquifer, and relatively high CAPEX associated with the development. Polymer on the other hand represents a relatively untested option for oil with viscosities of greater than 400cP as are present in this field. Modelling work used to identify risks and the subsequent development potential of these two options is presented. Potential development and maturation solutions for the various options are discussed and concepts are compared.