In order to improve oil recovery from water flooded heterogeneous oil reservoirs, different chemical enhanced oil recovery (cEOR) technologies can be applied. One of the recently developed cEOR technologies for the improvement of oil recovery is based on prefabricated polymeric nano-spheres. These spheres are able to swell over time through absorption of brine. Literature review on the flow of the nano-spheres in porous media showed that the mechanism of oil displacement from heterogeneous as well as homogenous porous media is not well established. One of the proposed mechanisms is that prefabricated polymeric particles might reduce the residual oil saturation S or (Goudarzi et al. 2014).To validate this, a series of core flood experiments was carried out in order to study this mechanism in both a heterogeneous Boise outcrop and homogeneous Bentheimer outcrop. Saturation of the cores with highly viscous crude oil was done at 50˚C using the porous plates method. After the oil saturated core was water flooded at 1 ft/day, a bump flood was performed. It helped to achieve the residual oil saturation in the core. Subsequently, several slugs of the nano-spheres were injected into the core in order to study the influence of the nano-spheres on the residual oil saturation. In addition to that, the propagation of the nano-spheres in the core was studied via a pressure drop measurement at different sections of the core and by effluent collection.The results of the experiments show that the oil displacement from a core with nano-spheres after a bump flood is marginal. Some oil extraction with nano-spheres might have happened due to restricting the flow in the highly permeable zones of the core. The subsequent injection of water could potentially result in improved microscopic sweep efficiency and increased oil production. However, in our experiments this effect was not significant. Our results do not show that nano-spheres significantly reduce the residual oil saturation of the core. Additional measurements showed that the nano-spheres are mostly retained in the inlet section of the core and the propagation of the nano-spheres in porous media is slow. Therefore, the effect of the extra oil recovery is likely limited to the inlet section of the core.There is currently limited description in the literature on the oil recovery mechanism by polymeric nano-spheres. It has a large impact on how the behaviour of the nano-spheres in porous media needs to be modelled and on the screening of candidate reservoirs for the conditions described in the experiments. In our experiments we have seen no significant reduction of residual oil saturation and slow propagation.Further work is required to evaluate the conditions under which the performance of the nano-spheres can be improved.
Summary When nanospheres are used for in-depth diversion in heterogeneous reservoirs, it is desired that spheres propagate deep into the reservoir along highly permeable zones with a resistance-factor (RF) buildup over time. This results in the reduced permeability of these reservoir zones and the diversion of subsequently injected water into unswept areas with higher oil saturation. Theoretically, a good propagation of the spheres can be achieved if their size is significantly smaller than the radius of pore throats. However, because of the interaction of nanospheres with each other and their swelling behavior, they can be retained without further propagation. Depending on the characteristics of the reservoir, the required deep propagation might not be realistic. Hence, it is important to study the influence of essential reservoir characteristics, such as brine salinity, saturation, and rock mineralogy, on the retention of the spheres in porous media. In this work, a series of coreflood experiments in Berea, Bentheimer, and Boise outcrop cores were performed to experimentally study the flow of nanospheres in porous media with different mineralogy and permeability. Complementary to that, the dynamic of the pressure drop over cores and the carbon content in the effluent were also analyzed at different injection flow rates. Dynamic light–scattering (DLS) tests indicated the size of nanospheres in different types of brine and helped to better understand their influence on the propagation in porous media. The results of the work show that the propagation of nanospheres in porous media is highly dependent on the brine salinity in cores with single- and multiphase saturations. For the same experimental conditions, the RF of nanospheres in porous media depends on the flow rate.
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