Plugging of Fractures in Carbonate Rocks by Nanocomposite Gels

Summary High water production is a common challenge during water-flooding of oil reservoirs. Improvement of volumetric sweep by blocking of fractures can improve the oil production and reduce the water production. The objective for the study was to investigate the potential for plugging of fractures in carbonate rocks using nanocomposite gels. Gelation was first investigated in experiments before dynamic experiments were modelled by using the simulator IORCoreSim, a core scale simulator developed at the IOR Centre of Norway. The rheology and gelation time for bulk solutions were determined by varying concentrations of nano-clay, polymer and cations. The most promising gels were further evaluated in flooding experiments using fractured chalk models. Simulations by IORCoreSim was used to model the gelation kinetics with different Laponite clay and HPAM concentrations, injection time, gel location and potential effect on oil recovery. Laboratory data were used as the basis for the simulations. In static experiments, the nano-clay formed weak to highly viscous gels. The strongest nanocomposite gels were formed together hydrolyzed polyacrylamide. Potassium, calcium and dissolved crushed chalk gave shorter aging time and stronger gels. Some glycols were found to retard the gelation reaction, but did not impair the strength of the gels. Flooding in fractured chalk models at 100% water saturation showed that both nanocomposite gels and nano-clay gels have potential to plug fractures in carbonate rocks. The IORCoreSim simulator was found to be appropriate to investigate the effects of Laponite/HPAM interactions with different gel component concentrations and conditions. Parameters for the calculation of gelation kinetics for Laponite/HPAM systems was tuned against the experimental results and then used as input in the simulations. IORCoreSim can also simulate placement and properties of Laponite/HPAM gels in fractured core plug experiments. Nanocomposite gels gave excellent gel strengths and they can plug fractures in carbonate rocks. Further evaluations of nanocomposite gels should be carried out at higher temperatures, with other brine compositions and with oil present. The gelation time can be delayed by adding retarders to the gelant solution, and this can allow longer transport of the gelant into target zones before formation of rigid gels. Nanocomposite gels showed good potential for plugging of fractures in chalks, and these gels can be environmentally friendly. The gels can also be used to improve volumetric sweep in geological storage of gases. The IORCoreSim model has potential to simulate placement of gels.