Production of mature oil fields emits significant amount of CO₂ related to circulation and handling of large volumes of gas and water. This can be reduced either by (1) using a low-carbon energy source and/or (2) reducing the volumes of the non-hydrocarbon produced/injected fluids. This paper describes how improved oil recovery techniques can be designed to reduce CO₂ intensity (kgCO₂/bbl oil) of oil production by efficient use of the injectants. It is shown that CO₂ emissions associated with injection of chemicals is strongly influenced by water cut at the start of the project, extent of the water cut reduction, and chemical utilization factor defined as the volume of produced oil per mass or volume of the injectant. As an example, for the oil field considered in this study, 3–8% reduction in water cut can result in 50–80% reduction in its CO₂ intensity. In addition to the incremental oil production with lower CO₂ intensity, the earlier implementation of enhanced oil recovery methods can extend the lifetime of the mature fields if carbon emission cut-offs are applied. In case of CO₂ enhanced oil recovery (EOR), the large storage potential for CO₂ can significantly reduce the overall CO₂ emissions of oil, albeit at a large energetic cost. For CO₂ EOR using CO₂ captured from gas power plants, improving the utilization factor from 2 bbl/tCO₂ to 4 bbl/tCO₂ can reduce the CO₂ intensity of the produced oil from 120 kgCO₂/bbl to 80 kgCO₂/bbl (33% reduction).

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.