## 3 Results and Discussion  
### Experimental Results  
A swelling test was conducted to obtain swelling factors at various pressures. Through the swelling test, the MMP could be estimated by understanding three distinct stages during the CO\({}_{2}\)-oil mixing processes, i.e., condensation, condensation-extraction, and extraction. The MMP can be determined when there is an intersection between condensation-extraction and extraction straight-line curves [14]. Not shown in Figure 2a, the CO\({}_{2}\)-ethanol mixture injection at 131 \({}^{\circ}\)F is the only case that shows decreasing swelling factor after the condensation stage occurs. However, a different phenomenon is shown by other cases with an increasing trend of swelling factor continuously until they reach maximum pressure, and then form miscible condition. Furthermore, it is believed that the CO\({}_{2}\)-ethanol mixed injection at 131 \({}^{\circ}\)F should have been miscible, as the experiment at 158 \({}^{\circ}\)F shows miscible condition at the same working pressure. Although no apparatus problem was verified and no experimental anomaly was proven, further evaluation should be conducted to answer that behavior [12]. Shadow from vibration rod may cause this strange phenomenon. The CO\({}_{2}\)-solvent mixture injection, for both acetone and ethanol, increases crude oil swelling factor values higher than pure CO\({}_{2}\) injection. Specifically, the CO\({}_{2}\)-acetone mixture swelling factor trend-line is slightly higher than the CO\({}_{2}\)-ethanol mixture for the two working temperatures. This means that acetone works better than ethanol in terms of swelling factor parameter. The VIT technique was applied to obtain the IFT values by which MMP of CO\({}_{2}\)-crude oil could be determined. The concept is that the IFT value of CO\({}_{2}\)-crude oil approaches zero when they become miscible, as no interface formed between these fluids afterward. Therefore, the MMP can be determined by linearly extrapolating the IFT values to the point of zero [15,16]. On the basis of the interpretation of Figure 3, it can be stated that co-solvents assist CO\({}_{2}\) to decrease the IFT between CO\({}_{2}\)-crude oil by which the IFT curves of co-solvent mixture cases drop faster than that of pure CO\({}_{2}\) injection. CO\({}_{2}\)-acetone mixture is the case that results in the lowest value of MMP. The MMP values of pure CO\({}_{2}\), CO\({}_{2}\)-ethanol, and CO\({}_{2}\)-acetone mixture injection at 131 \({}^{\circ}\)F are, respectively, 1667.36, 1552.86, and 1529.58 psia. Meanwhile at 158 \({}^{\circ}\)F, the values are 2049.95, 1812.86, and 1741.33 psia, respectively. From those MMP values, it supports the statement that acetone is the most effective co-solvent for assisting CO\({}_{2}\) to decrease the IFT between CO\({}_{2}\)-crude oil, and also the MMP as a consequence. Other research has shown that the influence of acetone is more significant on MMP reduction than other alcohol substances [17]. Figure 2: Swelling test results at (a) 131 \({}^{\circ}\)F and (b) 158 \({}^{\circ}\)F [12]. After the CO\({}_{2}\) injection experiments were performed, the remaining oil from VIPS apparatus was utilized for compositional analysis. The GC experiment was applied for compositional analysis of the original oil and the remaining oil after pure CO\({}_{2}\) and CO\({}_{2}\)-solvent mixture injection. The CO\({}_{2}\)-ethanol mixture injection is analyzed by GC at 131 \({}^{\circ}\)F of working temperature, while the CO\({}_{2}\)-acetone mixture injection is analyzed at 158 \({}^{\circ}\)F of working temperature. The working temperatures were chosen according to [PERSON] et al. [5, 18] and [PERSON] [19]. To clarify the cases, Table 3 displays the case's names with their description based on GC results. The performance of ethanol as a co-solvent is identified through a comparison among Cases 1, 2, and 3; a comparative analysis of Cases 1, 4, and 5 is done for acetone.