Enhanced Polymer Flooding - Reservoir Triggering Improves Injectivity and Eliminates Shear Degradation
W.J. Andrews, S.E. Bradley, P. Reed, M. Salehi and D. Chappell
Event name: IOR 2017 - 19th European Symposium on Improved Oil Recovery
Session: Polymer I
Publication date: 24 April 2017
Info: Extended abstract, PDF ( 2.41Mb )
Price: € 20
This paper describes a successful program of lab and pilot-scale studies qualifying a new shear-resistant, high-injectivity, reservoir-triggered polymer (Polymer) for field trial. The Polymer mitigates two of the major operational and economic challenges facing polymer flooding applications for mobility control, namely, shear degradation during injection and reduced fluid injectivity. Shear degradation of conventional HPAM polymers through injection facilities can result in dramatic losses of up to 70% of viscosity yield. However, this can be eliminated using the new Polymer. This is particularly important in an offshore environment where highly-shearing subsea chokes are required for flow distribution control. The Polymer formulation uses a novel yet inexpensive chemical approach enabling it to inject with near-water viscosity in a shear-resistant form. The Polymer has been engineered such that it does not viscosify the injection fluid until it is triggered in the reservoir away from the near wellbore region. Higher injection rates and viscosities can therefore be attained than would otherwise be possible with a conventional polymer flood. Methods: The Polymer’s triggering performance in porous media under both static and dynamic conditions has been demonstrated. The un-triggered Polymer has been subjected to extremes of shear at both lab and pilot-scale to test shear resistance. Injectivity of the Polymer has been assessed through an extensive suite of sand pack and coreflood experiments. Tests have also been conducted to verify the Polymer’s suitability for field deployment including surface storage, inversion, and long-term reservoir stability. Results: The Polymer is completely shear-resistant during injection, demonstrated by flowing through a scaled choke with pressure drops exceeding those expected during deployment. The viscosity of the un-triggered Polymer solution has been shown to be almost independent of the Polymer concentration, injecting with a viscosity close to that of sea water and giving excellent injectivity into sand packs and cores. In addition, the Polymer has been demonstrated to inject, propagate and trigger to deliver a pre-determined viscosity in a temperature-controlled 40ft sand pack experiment. The Polymer solution is easily and reliably prepared, out-performing a conventional HPAM in a pilot-scale inversion study, and demonstrates storage characteristics above the industry standard. A 15 month-long stability test performed at reservoir temperature with reservoir fluids showed minimal loss of viscosity. Testing will now proceed to field trial. If successful, this new technology offers a route to overcoming some of the key obstacles to large scale polymer EOR deployment, particularly in the offshore environment.