Heterogeneous reservoirs often have poor sweep efficiency during flooding. Although polymer flooding can be used to improve the recovery, in-depth diversion might provide a more economical alternative. Most of the in-depth diversion techniques are based on the propagation of a system that forms a gel in the reservoir. Premature cross-linking of the system prevents the fluid from penetrating deeply into the reservoir and as such reduces the efficiency of the treatment. We studied the effect of using a polyelectrolyte complex (PEC) to (temporarily) hide the cross-linker from the polymer molecules. In addition to studying the cross-linking process in bulk, we demonstrated its behaviour at the core scale (1 m length) as well as on the pore scale. The gelation time in bulk suggested that the PEC could effectively delay the time of the cross-linking even at high brine salinity. However the delay experienced in the core flood experiment was much shorter. Tracer tests demonstrated that the XL polymer, which is a mixture of PEC and partially hydrolyzed polyacrylamide, reduced the core pore volume by roughly 6.2% (in absolute terms). The micro-CT images showed that most of the XL polymer was retained in the smaller pores of the core. The large increase in dispersion coefficient suggests that this must have resulted in the creation of a few dominant flow paths isolated from each other by closure of the smaller pores.

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The size distribution and swelling kinetics of copolymer nano-spheres extracted from an W/O emulsion was studied with dynamic light scattering (DLS) and transmission electron microscopy (TEM). TEM results were compared against DLS results. It was demonstrated that the size distribution for agglomerates (clusters) of particles match well with the size distribution obtained from DLS. Hence, less time consuming DLS tests can be used for the estimation of the size of nano-spheres in the future. Next, a novel procedure for the study of agglomeration and swelling rates separately with TEM was designed. The results of the study revealed that the spheres agglomerate and swell over time. The kinetics of the agllomeration is used for a population balance model to predict the size of spheres over time. This approach helps to understand how well the spheres can propagate in an oil reservoir over time.@en

In many oil fields, water is injected into a reservoir to displace oil to the production wells. During the injection process, oil is pushed by water towards production wells which have a lower pressure than the rest of the reservoir. If the reservoir is homogeneous, then a good sweep efficiency of the water flood process is expected. However, most oil reservoirs are stratified and that creates a permeability contrast along the whole height. High permeable layers take most of the injected water resulting in lower sweep efficiency of the other layers. The water breaks through the high permeable zones, significantly increasing the water cut of the produced fluid. Excessive produced water has to be treated in surface facilities which increase the costs of the extraction process. Another disadvantage of the low sweep of a reservoir is a significant amount of remaining oil behind the displacement front...@en

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 Sor (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.@en