Investigation of Miscibility Behavior of CO2 rich Hydrocarbon Systems – With Application for Gas Injection EOR

Abstract

The phase behavior of two Middle East reservoir fluids mixed with CO 2 has been studied. The experimental work includes quantification of VLLE/LLE behavior studied in a visual high pressure PVT cell.To investigate the effect of dispersion on slim tube recoveries, experiments were performed using two different tube sizes. One of the reservoir fluids was found to be miscible with CO 2 at the reservoir temperature while a liquid-liquid split persisting at high pressure was observed for the other fluid. As the two liquid phases had approximately the same mobility, a high slimtube recovery was seen for the latter fluid despite the liquid-liquid split. EOS models have been developed matching the swelling and slimtube data and confirming the observed VLLE and LLE phase behavior.The work has led to an improved understanding of how swelling and MMP data for CO 2 -crude oil systems is to be interpreted. An important observation is that a miscible drive is not always attainable for a reservoir fluid undergoing CO 2 gas injection.

Study of Liquid–Liquid and Liquid–Liquid–Vapor Equilibria for Crude Oil Mixtures with Carbon Dioxide and Methane Using Short-Wave Infrared Imaging: Experimental and Thermodynamic Modeling

“…When pressure continues to decrease, LL equilibria are more evident and droplets start to grow until they resemble the LV transition with big droplets dispersed in the oily phase. This liquid dispersed phase was associated in the literature with a dense and CO 2 -rich phase that also solubilizes some crude oil compounds. ,,, It is important to mention that no phase segregation is observed during depletion, indicating that the high dispersity is related to density similarities between the two liquid phases. ,,, Under lower temperatures and pressures conditions, close to critical conditions of pure CO 2 , an LLV equilibrium is detected, as presented in Figure C. Visually, this phase transition is not evident but the compressibility change in the system reveals the vapor phase evolution, as previously presented in Figure .…”

“…This liquid dispersed phase was associated in the literature with a dense and CO 2 -rich phase that also solubilizes some crude oil compounds. 29,43,44,74 It is important to mention that no phase segregation is observed during depletion, indicating that the high dispersity is related to density similarities between the two liquid phases. 3,29,52,53 Under lower temperatures and pressures conditions, close to critical conditions of pure CO 2 , an LLV equilibrium is detected, as presented in Figure 5C.…”

“…The LLV equilibria occurrence was reported for light − and heavy crude oil systems, − usually under low reservoir temperatures conditions with high gas content. For these systems, the influence of LLV on crude oil recovery, , along with their proper representation by process simulators, − is still a scientific challenge. However, similarities were reported between CO 2 + crude oil and CO 2 + alkane phase behavior.…”

“…Through these analyses, the formation of two independent liquid phases was observed, one of them oleic and the other a gas-rich phase. Moreover, it was reported that the gas-rich phase solubilizes some crude oil compounds, becoming denser and darker. ,,, For this reason, one of the main problems for phase equilibria identification is its opaque nature, together with the poor phase segregation because of densities similarities for the different liquids. ,,, Consequently, spectrometric analyses was used for darker crude oil phase behavior characterization …”

Measurement of Fluid Phase Equilibria for High Gas Ratio Mixtures of Carbon Dioxide, Methane, and Brazilian Presalt Crude Oil

“…Additionally, LLE is observed for crude oil mixtures with a high CO 2 content at least 6 °C above the LLVE upper critical point. ,, The same phase behavior was found for model systems for methane/CO 2 /hexadecane or propane/CO 2 /hexadecane mixtures. , This equilibrium is characterized by high dispersity and low segregation that constrain the detection of CO 2 in PVT analysis. − The appearance of the LL region can be affected by the composition of the mixed gas. For example, increasing the composition of the intermediate molecular weight compounds results in a reduction in the LLVE region; as well, the compositional variations in crude oil, , e.g., PNA distribution could affect the multiphase region of the fluid .…”