Numerical and Experimental Study of Enhanced Shale-Oil Recovery by CO₂ Miscible Displacement with NMR

Abstract

CO 2 miscible displacement is an efficient method for enhanced shale-oil recovery. Understanding the movability of shale oil in different states of occurrence is important for CO 2 miscible displacement. Therefore, a nuclear magnetic resonance (NMR)-based CO 2 miscible displacement experiment is conducted on oil-saturated shale and sandstone. To describe the processes involved in the measurements, a mathematical model based on the Maxwell−Stefan equation is developed; it considers the heterogeneity of shale and the competitive adsorption and absorption of CO 2 −oil mixtures in organic matter. The results show that the porosity of immobile oil in the shale samples (4.0% and 4.3%) is lower than the porosity of free oil (8.0% and 10.2%). Compared with sandstone, a larger CO 2 -injection time yields a smaller recovery factor in the case of shale, and the recovery factor of immobile oil is much less than that of free oil in the shale. According to the model, the order of oil production in the laminated shale during CO 2 miscible displacement is as follows: free oil in the inclusions, free oil in organic matrix-clay, and adsorption and absorption of oil in organic matter. The oil production rate is associated with the heterogeneity of shale (R 0 ) and the competitive adsorption and absorption of CO 2 -oil mixture in the organic matter (ω 0 , k ads ).

Experimental Study on Enhanced Shale Oil Recovery and Remaining Oil Distribution by CO2 Flooding with Nuclear Magnetic Resonance Technology

“…Figure shows the NMR T 2 spectral distribution curves of core # 9 during CO 2 flooding. Because the amplitude of the signal is proportional to the number of hydrogen nuclei, it is positively correlated with the oil content in the pores. Because of oil displacement, the amplitude of the T 2 signal decreases with the development of the CO 2 flooding process .…”

“…When the displacement pressure is higher than the MMP, CO 2 and the crude oil are in a miscible state. The mechanism of CO 2 miscible displacement is as follows: in addition to reducing the viscosity and swelling of the crude oil, CO 2 miscible displacement can also extract the light hydrocarbon components of the crude oil through the extraction process, which enriches the displacement front and reduces the interfacial tension, which reduces the saturation of the remaining oil. In addition, CO 2 in the miscible phase can not only extract and vaporize light hydrocarbons in crude oil but also form a CO 2 –light hydrocarbon-mixed oil belt.…”

“…Wei et al (2019) carried out CO 2 and N 2 flooding experiments on shale rocks, and the recovery rates of CO 2 flooding and N 2 flooding were 38.4 and 35.1%, respectively. Zhu et al (2019) carried out experiments on CO 2 miscible flooding of shale and sandstone based on nuclear magnetic resonance (NMR), divided shale oil into immobile oil and movable oil, and analyzed the recovery efficiency of shale and sandstone miscible flooding. Du et al (2020) conducted a comparative study on the effects of CO 2 flooding and CO 2 huff and puff in tight/shale oil on the oil recovery factor (ORF).…”

A Minireview of the Influence of CO2 Injection on the Pore Structure of Reservoir Rocks: Advances and Outlook

“…Huang et al 40 compared the displacement efficiency of SO 2 and CO 2 for shale oil samples and explained the differences in oil displacement with the aid of the low-field NMR. Zhu et al 42 studied the performance of CO 2 miscible displacement of shale oil by means of numerical simulations and NMR. Through the NMR experiments, Huang et al 43 carried out CO 2 flooding experiments on samples with different pore structures under various displacement pressures and evaluated the effects of petrophysical properties, pore structure, and clay minerals on CO 2 flooding efficiency.…”

Effects of Pore Structures on Seepage and Dispersion Characteristics during CO2 Miscible Displacements in Unconsolidated Cores

“…Currently, carbon dioxide enhanced oil recovery (CO 2 -EOR) technology has attracted increasing attention, and approximately 20% of the total oil recovery uses CO 2 -EOR technology worldwide. − The oil recovery is obviously improved when supercritical CO 2 is injected, which results in a high oil displacement efficiency. At the same time, large amounts of CO 2 remain under the ground, which achieves an outstanding emission reduction. − …”