Polymer EOR Evaluation on Karstified Carbonates

12 October 2022

Waterflooded oil fields can offer additional opportunities to increase ultimate recovery. In-depth understanding of the project and the selection of the most appropriate technology are key to conduct such project to an economical success.

Polymer flooding is known to provide an effective solution to compensate for unfavourable mobility ratios between oil and injected water. It creates more stable displacement fronts, and therefore increases sweep efficiency which in turn will lead to a major recovery.

A proper design and execution plan of the polymer injection programme is a prerequisite for dual-media reservoir as often encountered in naturally fractured carbonate fields. Multiple conditions have to be realised to initiate a fracture-matrix counter current flow. Thus, a virtuous cycle would be triggered where the displacement front progressively slows down, further increasing the efficiency of the displacement process.

Ad Terra Energy is currently providing a full lifecycle support to one of our clients in adapting polymer technology to the current field operations. It includes among others: conceptual and economical assessment, feasibility study, multi-scale modelling and numerical simulation, coordination of lab studies, and the design and implementation of the pilot prior to field scale development. After having completed the initial stage of the project, we are assisting our client in a massive data acquisition plan including multiple injectivity tests in different reservoir targets.

Injector to producer cross-section from high resolution simulation model showing polymers effect on water viscosity.
2D view from the simulation model showing average residual oil after 2 years of alternate polymer injection
Polymer interaction on a matrix-fracture system at an intermediate point of a cyclical injection process. The polymer injection resumes, but the saturation condition behind the front is different in comparison to when injection stopped. The water saturation is lower and the oil saturation is higher because oil and water exchange between matrix and fracture. Consequently, the polymer slug mobility is reduced with the displacement front moving at a reduced velocity (V2<V1) and advancing a shorter distance within the fractures system for the same injection period (Dx2<Dx1)
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