Enhanced oil recovery by carbon dioxide and diethyl ether as mutual solvents




Alzayer, Ahmed Jamal

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Increasing the oil recovery factor from existing fields is the key towards meeting future oil demand. The injection of solvents, an established EOR technique, has shown significant improvement in oil recovery over conventional water floods. However, the injection of pure solvent slugs can be quite costly for field operators. To mitigate this problem, recent literature has suggested the use of brines that are saturated with mutual solvents (dissolve in both oil and water) such as Carbon Dioxide (CO₂) and Dimethyl Ether (DME). This practice minimizes the amount of used solvent since it is governed by its limited solubility in water. The solubility of CO₂ and DME is much higher in oil than in water. Therefore, a mass transfer takes place once CO₂ or DME saturated brines come into contact with oil. As these solvents go into the oil phase, they promote oil swelling and reduce the oil viscosity, thereby making it movable and increasing the oil recovery as a result. Although there has been recent lab work performed with this EOR method, most of the work performed so far involved short cores, high injection rates and in some cases limited to sandstone cores. In this thesis, we investigated the effect of using brines that were saturated with CO₂ and Diethyl ether (DEE) on oil recovery. The results came out to be mixed and not completely in line with previous literature for CO₂ rich brine (Carbonated Water). Injecting carbonated water into sandstone cores did not improve the oil recovery. However, there was an improvement in oil recovery as a result of carbonated water injection in carbonate cores, which also displayed effluent line plugging. For the case of DEE-rich brine, there was a noticeable improvement in oil recovery but it took more pore volumes to have an effect in comparison to DME-rich brine literature results. The experimental work was further supplemented with numerical modeling. The simulator was not able to capture the effects of carbonated water observed in the experiment, due to the absence of rock–fluid interaction in the modeling mechanism. In contrast, the DEE rich brine case was successfully matched with the compositional simulator since it did not involve rock reactions and was strictly based on fluid–fluid interactions


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