Experimental Investigation of Low-Concentrated Nanocomposite Polymer Gels for Water Shutoff Treatment Under Reservoir Conditions

Abstract

Summary Excessive water production is one of the main challenges in mature oil fields. Applying polymer gels has proven to be an effective chemical treatment to this problem. Because of some limitations in application of polymer gels in oil reservoirs with harsh conditions, using nanoparticles (NPs) in gel structure has been proposed recently to improve the performance of such systems. However, while main body of the previous studies has only focused on improvement of bulk properties of polymer gels in presence of NPs, there is a serious lack of data on their performance in porous media. In this study, we have conducted a comprehensive investigation on application of two new nanocomposite polymer gels through bulk-gel static tests and dynamic core displacement tests. Fe2O3 and NiO NPs at low concentrations (<100 mg·L−1) in AN125VLM/chromium acetate polymer gel system were used. The results of bulk bottle tests at 82℃ demonstrated that the nanocomposite gel systems have the same gelation time and gel strength as the NPs-free gel. Swelling ratio measurements were also performed in a high-salinity formation water (268 949 mg·L−1), and accordingly, while NiO NPs deteriorated the swelling behavior of the gel system, Fe2O3 NPs showed a positive impact. The results of the strain-sweep test demonstrated relatively similar linear viscoelastic region and thus the same gel strength for all gel samples. In addition, the results of the thermogravimetric analysis (TGA) revealed that Fe2O3 NPs had a minor positive impact on thermal resistance of the polymer gel system. Finally, high pressure-high temperature coreflooding experiments were carried out on three sandstone reservoir core samples. Although the NPs-free gel showed a desirable level of disproportionate permeability reduction, the injection of Fe2O3 nanocomposite gel showed unsatisfactory results and caused rock permeability degradation. The pressure drop trend and deposition of polymer gel particles at the upstream injection side confirmed the aggregation and plugging effect of NPs during injection. Our findings demonstrate the critical aspect of dynamic core displacement testing of nanocomposite gels before their use for field applications.