Enhanced Fill-Up Response and Recovery with Secondary Polymer Injection vs. Tertiary Polymer Injection: A Field-Scale Pilot
Authors: Juri J. E. , Serrano V. , Guillen P. , Campos H. , Zurletti A. , Martinez D. , Ruiz A. 
Published: April 2024

Efficient reservoir management often involves optimizing the injection of polymers to enhance oil recovery while minimizing resource waste. The advantage of secondary vs. tertiary modes has been always rely on corefloods results. Historically, concerns about polymer wastage during the filling phase (fill-up a depleted reservoir) have discouraged the use of secondary polymer injection. However, our study challenges this conventional wisdom through a comprehensive analysis of composite core coreflood experiments and two pilots in the same reservoir.

To establish the most favorable displacement sequence, we conducted a pilot study involving secondary polymer injection in the same reservoir where we had previously implemented water injection at matched depletion pressures, followed by tertiary polymer injection. We meticulously monitored the oil response in terms of injected pore volumes.

Our findings reveal two key advantages of secondary polymer injection over its tertiary counterpart, with profound implications for field-scale operations. Firstly, secondary polymer injection demonstrates the ability to retard water production, thereby increasing the recovery factor when compared to both baseline waterflooding and tertiary polymer injection with an equivalent polymer volume. Secondly, secondary polymer injection accelerates oil production, particularly in the early stages. This acceleration translates into better economic indicators and final recovery rates for secondary polymer injection. Additionally, in fluvial systems, the remaining oil after water injection followed by secondary polymer injection seems to be greater than that achieved with tertiary polymer injection.

Our results demonstrate that secondary polymer injection significantly reduces the fill-up time, being 2.3 times faster than the sum of the recovery achieved with tertiary polymer injection and initial water injection in the tertiary polymer pilot. This efficiency is attributed to a piston-like displacement mechanism, particularly advantageous in fluvial systems with multiscale surfaces that promote viscous crossflow conditions. The shortened fill-up time and enhanced recovery observed with secondary polymer injection translate into reduced infrastructure and water supply requirements. Using these findings, we have devised an efficient field development plan that replaces large-scale water injection and tertiary polymer injection facilities with a hierarchical, zone-by-zone approach to secondary polymer development. This strategy not only reduces initial capital exposure but also rationalizes polymer consumption. Furthermore, the use of secondary polymer injection significantly enhances vertical conformance when compared to tertiary polymer injection.

In conclusion, our study challenges conventional practices by demonstrating that secondary polymer injection offers superior performance in terms of fill-up response and final recovery compared to tertiary polymer injection. These findings open new avenues for optimizing reservoir management, promoting economic efficiency, and minimizing environmental impact.