In gas flooding EOR applications the injection pressure plays a significant role. It has to be higher than the minimum miscibility pressure (MMP) for a fully miscible flood to obtain the highest oil recovery, since the swelling, and consequently the efficiency of a flood, strongly depends on the miscibility of the residual oil and the recovery fluid. Poor miscibility leads to poor recovery. On the other hand the injection pressure must not be higher than the reservoir fracture pressure to avoid the creation of high thief zones in the formation. The addition of proper additives to the injection gas can reduce the MMP significantly. Using a pressure resistant sapphire cell firstly the solubility of different additives in the gas at common reservoir conditions was determined. The compatibility of the additives with CO2 is needed to be ascertained first in order to identify compounds that enable an easy co-injection of the additive within the flow of the CO2. Then the miscibility behavior of the gas and a model oil was studied and the change of the miscibility pressure in the presence of chosen additives was investigated. Phase behavior studies at typical reservoir pressures and temperatures show the miscibility behavior of the fluids and the effect of the different additives on the mutual miscibility. It was proven that the minimum miscibility pressure can be lowered significantly by the choice of an appropriate additive. Through determination of phase diagrams it is shown how the miscibility gap between crude oil and CO2 can be decreased, thereby going from immiscible or multi-contact miscible to fully miscible conditions. Adjusting the MMP broadens the pressure range of high sweep efficiency that is limited by the formation fracture pressure as the upper and the MMP as the lower limit. Thus, conditions can be created at which the reservoir pressure leads to fully miscible floods. Using an appropriate additive can lead to an improvement of the miscibility behavior at given reservoir conditions and make it more favorable for a CO2 EOR process. A former near-miscible or even immiscible application can become a miscible flood. By this the sweep efficiency is maximized and the recovery rate is highest. The parameters that define an economic reasonable gas flooding application now comprise a larger number of reservoirs due to the improved miscibility of crude oil and injection gas.

The surfactant selection for chemical floods usually starts with an extensive lab study identifying the formulation that provides the best recovery performance. However, it is oftentimes overlooked that in a laboratory setting the requirements on product availability and applicability are less sensitive than for a field scale injection. Thus, there are various other aspects that contribute to the overall economics of chemical selection which also need to be taken into account. Aside from the molecular properties, the manufacturing aspects have to be examined carefully to allow proper planning and ensure the supply of large volumes for full field implementation on time. Furthermore, opportunities to simplify and optimize the logistics (i.e. packaging, regulatory compliances …) help to reduce the cost of a chemical injection project. This is also strongly connected with the handling properties of the selected materials when it comes to the blending of the final injection cocktail (e.g. activity, viscosity, storage conditions, etc…). This paper describes the crucial factors that impact the economics of a selected surfactant for a chemical EOR project, taking into account the production, transportation, delivery form, application performance, handling, amongst others. Another point that will be discussed, is the option to create in-country value and reduce logistic challenges by performing a final production step regionally close to the project site. In the end, we conclude that involving the suppliers at a very early stage of the screening process helps to eliminate unsuitable molecules. It also allows for proper planning and leads to the most appropriate procedure. By taking into account the whole economics picture, a win-win situation can be created and the project is beneficially optimized. Forward thinking the treatment of both injected and produced fluids can be part of this optimization process.

CO2 injection is a commonly used technique for recovering residual oil from mature reservoirs. It gains more and more interest due to the importance of carbon dioxide capturing and sequestration. The increasing CO2 availability and the easy implementation make this Enhanced Oil Recovery (EOR) method favorable in times of low oil prices. In most reservoirs injected or native CO2 exists in its supercritical state (scCO2) because the critical point of carbon dioxide is at a lower pressure and temperature than the reservoir conditions. Its miscibility behavior makes scCO2 a good solvent that generates high oil recovery rates. The swelling of the hydrocarbon phase, and consequently the efficiency of a flood, strongly depends on the miscibility of the residual oil and the solvent. Therefore, immiscibility of scCO2 with the crude oil leads to poor recovery, which poses some limitations to CO2 EOR procedures. Additionally, viscosity or gravity effects could decrease the sweep efficiency and therewith the recovery rate. The miscibility of the injection fluid and the residual crude oil can be improved by solubilizing an appropriate additive in the scCO2. In this work the compatibility of different additives with scCO2 is investigated in order to identify compounds that enable an easy co-injection of the additive within the flow of the CO2. Phase behavior studies under typical reservoir pressures and temperatures with a (model) crude oil show the solubilization behavior of the recovery fluid CO2 and the effect of the different additives on the mutual miscibility. Information about the influence of different additives on the crude oil's miscibility and swelling with the injected CO2 allows conclusions about the best procedure for each reservoir. The additives can also interact with the formation water and build stable CO2-foams downhole. These foams exhibit a higher viscosity than the pure gas which also results in improved sweep efficiency. Using an appropriate additive can lead to a change of the miscibility behavior of a reservoir and make it more favorable for a CO2 EOR process. A former near-miscible or even immiscible application can become a miscible flood. Furthermore, the additives can influence the performance of water alternate gas (WAG) and foam methods and lead to higher recovery rates.

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