A case study of salt-tolerant functional polymer for EOR in carbonate reservoirs with ultra-high salinity

Abstract

Copyright 2020, Society of Petroleum Engineers. In this work, we present a new-type salt-tolerant functional polymer (CBHB) for ultra-high salinityconditions, and investigated its feasibility for polymer flooding in a fractured carbonate reservoir with asalinity of more than 220000 mg/L (Ca2+ + Mg2+ > 10000 mg/L) in Akanskoe oilfield (Tatarstan, Russia).First, the properties of the salt-tolerant functional polymer (CBHB), including solubility, rheologicalparameters, and long-term stability etc., were evaluated at different salinity conditions and comparedwith current commercial polymers (total 15 samples). Then, the static and dynamic adsorption weredetermined using UV-spectroscopy. Finally, regular filtration experiments on a laboratory scale and 4DX-ray tomography core flooding experiments were carried out at reservoir conditions to analyze themicroscopic/macroscopic displacement mechanism and efficiency of polymer in real time. The results showed that only three polymers can be dissolved at 227500 mg/L salinity and 23 °C (reservoirtemperature) and give homogenous solution with the viscosity of higher than 100 mPa·s at the polymerconcentration of 2000 mg/L. CBHB showed the highest viscosity of 830 mPa·s after aging for 180 days, which means that it has a superior salt tolerance ability. 4D X-ray tomography indicated that polymerdisplacement front is aligned and even oil in some small pores or caves can be also displaced with almostno oil film left due to a good viscoelasticity of polymer. A high displacement efficiency of 72.94% wasachieved. This means that this CBHB polymer not only has the traditional mobility control capacity toincrease sweep efficiency, but also have ability to increase displacement efficiency, which makes CBHBpolymer have a great potential for EOR in ultra-high salinity reservoirs. Salt-tolerant functional CBHB polymer for ultra-high salinity of more than 220000 mg/L (Ca2+ + Mg2+> 10000 mg/L) was developed. It exhibited both high sweep and displacement efficiency due to itsfunctional groups. This will expand the application of polymer flooding for ultra-high salinity reservoirs. Simultaneously, 4D X-ray tomography was innovatively used to precisely investigate the microscopic/macroscopic displacement mechanism and efficiency of polymer flooding.