CO2-Oil Minimum Miscibility Pressure Estimation for the Omani Oils

CO2 injection in an oil reservoir is an EOR method that is widely known for its higher oil ultimate recovery and for its use in the Carbon Capture and Storage (CCS) that leads to desirable benefits on the environment (reducing CO2 content in the atmosphere). In the CO2 flooding method, favorable conditions of reservoir pressure, temperature, and oil composition are required to achieve the dynamic or multiple-contact miscibility displacement of injected CO2 and oil reservoir. The multiple-contact miscibility can be defined as the thermodynamic equilibrium between the CO2 gas and the reservoir oil fluid. In otherwords a complete mass transfer of the CO2 gas into the reservoir oil fluid is defined as a condensing process, and the transfer of reservoir oil components to the CO2 gas is defined as a vaporizing process. It is worthwhile mentioning that the miscibility with the oil at injection pressure of Minimum Miscibility Pressure (MMP) occurs at CO2 supercritical conditions, which is the optimum condition to become an efficient solvent. In addition, the CO2-Oil interaction causes the oil to be swelled, the oil viscosity to be reduced, and the interfacial tension to be minimized. All these three factors allow the oil to flow more easily in the reservoir rock and thus increase production resulting in higher oil ultimate recovery. Accurate prediction of CO2-oil MMP is the most important key step required for the design of CO2 miscible flood. Therefore, it is advisable to determine the CO2-oil MMP for the correct specific candidate oil field under the representative. In otherwords, the oil producing company should not rely on the various correlations found in the literature that are not based on the Omani oil reservoirs. This could lead to inaccurate estimate of the MMP. The purity of the injected CO2 gas affects the MMP. The main CO2 impurities that increase the MMP are Methane (C1) and Nitrogen (N2). These should be incorporated in the development of the mathematical correlation of the CO2-oil MMP. The methodology adopted in this research study involves two parts; part-1, includes the experimental work based on the Slim-Tube, Rising Bubble and Vanishing Interfacial Tension experiments to measure CO2-oil MMP for selected Omani oils from different reservoirs in Oman, and part-2, contains the mathematical calculation of the of CO2-oil MMP. Part-1; There are different methods of measuring the CO2-Oil MMP, and they are as follows; 1- Slim-Tube 2- Rising Bubble 3- Vanishing Interfacial Tension In this research study all the above mentioned methods are considered for the measurement of the CO2-Oil MMP. The Slim-Tube consists of a long (about 12.2 m) with small diameter (0.64 cm) and high pressure tube. This tube is packed with clean sand or glass beads in order to reach a fluid permeability of 3 to 5 Darcies. During the experiment the Slim-Tube is saturated with the reservoir oil to be studied and the full apparatus is kept in the oven at the reservoir temperature. CO2 is then injected at different increasing pressures till miscible displacement is achieved at the MMP, at which case 95% of the oil is recovered. These experimental runs should be done for pure CO2 and impure CO2. The Slim-Tube and Vanishing Interfacial Tension equipments are not available in the PCE department laboratory and the SQU otherlaboratories. Part-2 This part of the research study contains the development of a mathematical correlation based on the resulting MMP values from the experimental work in Part-1. The CO2-Oil MMP mathematical correlation for the different selected Omani oil reservoirs should be based on pure CO2 and impure CO2. Impure CO2 gas is more common and can be found in the flue gas and Natural gas. The mathematical correlation model to calculate the CO2-Oil MMP is envisaged to be developed by different methods. Sensitivity runs on the CO2-oil MMP by comparing the different mathematical techniques with the experimental results in order to validate the accuracy of the mathematical correlation to calculate the CO2-oil MMP