Secondary and Tertiary Polymer Flooding in Extra-Heavy Oil: Reservoir Conditions Measurements - Performance Comparison
Authors: Fabbri C. , Cottin C. , Jimenez J. , Nguyen M. , Hourcq S. , Bourgeois M. , Hamon G. 
Published: March 2015

Abstract
In the challenging context of heavy to extra heavy oil production, polymer flood technology appears to be a promising solution to enhance ultimate recovery of reservoirs. Several field applications have already shown the efficiency of such technologies, although the final incremental recovery and mechanisms involved are still poorly understood. Indeed, the characteristics of the viscous fingering effects that certainly play a role are rarely captured at the field scale or at the core scale.
This work aims at comparing the results of two core experiments with polymer flood in secondary and tertiary mode, in reservoir conditions, in term of recovery as well as in terms of relative permeabilities. In both cases, experiments were carried out on reconstituted reservoir cores, with restored wettability, initially saturated with live oil partially degassed in a PVT cell to the expected pressure and viscosity at the start of the field test. Saturation profiles were measured with X-Ray scans; effluents were collected in test-tubes and analyzed by UV measurements. Additional follow-up with tracers was tested in order to better assess the breakthrough of different fluids as well as the polymer adsorption during the experiment. Although the viscosity ratio was still highly unfavorable, with a polymer bulk viscosity around 70 cP at 10s-1 and an oil viscosity estimated at 5500 cP, polymer floods exhibit an excellent recovery factor.

Introduction
Field applications of polymer flood have been focused during several years on medium viscosity oil. Due to its relatively low impact on the environment as well as its lower cost compared to thermal methods, polymer flood in the context of heavy to extra-heavy oil has gained a lot of attention from the academic and industrial world, especially for highly viscous but mobile oil.
Moreover, several field cases have already shown the applicability of polymer flood to very viscous oil such as the ones of Pelican Lake field (Delamaide et al. 2013). In this context, it is necessary to be able to forecast production as correctly as possible. Estimating reserves associated with polymer injection have lead to a need for better understanding and representation of these complex flows. Moreover, the consequences of primary depletion as well as water flooding on the results of the polymer flood are still poorly understood, although these could be crucial to better optimize the production development of the field.
The aim of this experimental study is to differenciate the efficiency of secondary and tertiary polymer flood. In order to do so, cores were prepared in both experiments with the same procedure, so as to reproduce the permeability of the unconsolidated sand of the reservoir. Cores were aged in order to restore the wettability state as close as possible as the one in the field. The fluid was recombined also with the same amount of gas in both experiments so as to reach the reservoir viscosity (5500 cP). The same polymer viscosity (70 cP at 10 s-1) was targeted for both floods. The effluents have been carefully quantified by solvent and UV detection, in order to be able to correctly conclude from both experiments. Based on experimental results, a consistent methodology is described to derive polymer-oil relative permeabilities in the context of heavy to extra-heavy oil.