A New Dynamic Fluid Flow Method for Studying the Phase Changes of the Light/Heavy Crude Oil-Solvent Systems

In this thesis, a novel experimental method, namely, the dynamic fluid flow (DFF) method, was developed to study the phase changes of various light/heavy crude oil‒solvent systems. First, two series of constant-composition-expansion (CCE) tests and constant-composition-expansion and compression (CCEC) tests were conducted by using a pressure‒volume‒temperature (PVT) system. Second, a series of the DFF tests were undertaken to measure the pressure gradients along a long micro-tubing at different outlet pressures when a given light/heavy crude oil‒solvent mixture flowed at a constant volume flow rate. For the light crude oil‒CO2 systems, it was found that the pressure gradient remained low and almost constant as long as the outlet pressure was above the bubble-point pressure of the light crude oil‒CO2 system. However, the pressure gradient was suddenly increased once the outlet pressure was below the bubble-point pressure because the light crude oil‒CO2 system changed from one liquid phase into liquid‒gas two phases. The linear regression was applied to obtain the measured pressure gradient versus outlet pressure line in each case. The outlet pressure at the intersection point of the two lines, where a sudden slope change occurred, was determined to be the bubble-point pressure. It was also found that for the same light crude oil‒CO2 system, the measured bubble-point pressures from the DFF tests were close to but slightly lower than those measured from the CCE tests due to the micro-tubing confinement and gas bubble re-entrainment. Furthermore, a mathematical formula was derived to predict the length of the two-phase flow region at a different outlet pressure below the bubble-point pressure. For the heavy crude oil‒solvent systems, it was found from the CCE tests that the measured Pcell‒νmix data could be divided into two or three regions, depending on the solvent concentration. For the heavy crude oil-solvent system with a low solvent concentration, its measured Pcell‒νmix data had three different regions (I, II, and III). The higher pressure at the intersection point of Regions I and II was referred to as the bubble-point pressure and the lower pressure at the intersection point of Regions II and III was referred to as the pseudo bubble-point pressure. For the heavy crude oil-solvent system with a high solvent concentration, its measured Pcell‒νmix data had two regions (I and II) only. The pressure at the intersection point of the two regions was referred to as the bubble-point pressure. In this case, the pseudo bubble-point pressure could not be obtained. It was found that the heavy crude oil-CH4 system had not only the highest bubble-point pressure and pseudo bubble-point pressure but also the largest difference between these two threshold pressures, in comparison with the heavy crude oil-CO2 system and the heavy crude oil-C3H8 system at the same solvent concentration. These facts indicate that CH4 not only is the most volatile solvent but also can be dispersed as gas bubbles to induce a stable foamy oil in the largest pressure range, in comparison with CO2 and C3H8. In each DFF test of the heavy crude oil‒solvent system, the measured pressure gradient vs. outlet pressure data could be divided into three regions (I, II and III). For all the heavy crude oilsolvent systems tested except the heavy crude oil-C3H8 systems with high C3H8 concentrations, the higher outlet pressure at the intersection point of Regions I and II was determined to be the bubble-point pressure. The lower outlet pressure at the intersection point of Regions II and III was referred to as the pseudo bubble-point pressure. For the heavy crude oil-C3H8 systems with high C3H8 concentrations, however, the higher outlet pressure at the intersection of Regions I and II represented a phase-change pressure, at which a two-liquid phase flow occurred in the micro-tubing. The lower outlet pressure at the intersection point of Regions II and III was determined as the bubble-point pressure. A mathematical model based on the CCE test results was derived to study the gas bubble nucleation processes in different heavy crude oilsolvent systems. A newly defined quantity called the bubble nucleation index (BNI) was used to represent the strength of bubble nucleation. The ratio of the solvent concentration at each pressure step in the CCE test to that at the equilibrium state, c_CCE/c_eq, was used to represent the degree of supersaturation. It was found from the BNI vs. c_CCE/c_eq data that there was a threshold degree of supersaturation for gas bubble nucleation to take place for the heavy crude oil-CH4 system and heavy crude oil-C3H8 system. However, there was no such threshold degree of supersaturation for the heavy crude oil-CO2 system. By comparing the degrees of supersaturation of different heavy crude oil-solvent systems, it can be concluded that in comparison with CO2 and C3H8, CH4 is the easiest solvent that can be nucleated from the heavy oil and the heavy crude oil-CH4 system has the lowest degree of supersaturation in comparison with the other two heavy crude oil-solvent systems. Three CCEC tests of three different heavy crude oil-solvent systems were conducted and another mathematical model was formulated based on the CCEC test results to study bubble liberation. Another new quantity, namely, the bubble liberation index (BLI), was defined to denote the strength of bubble liberation. By comparing the BLIs of different heavy crude oil-solvent systems, it was found that CH4 was the most difficult solvent to be liberated from the heavy oil in comparison with CO2 and C3H8. Also, the heavy crude oil could hold and contain more bubbles of CH4 than the other two solvents. Therefore, CH4 can induce the strongest and most stable foamy oil in comparison with CO2 and C3H8.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Doctoral -- first

Discipline thesis:degree_discipline

Engineering - Petroleum Systems

Grantor dc:publisher

Faculty of Graduate Studies and Research, University of Regina

Year dc:date.issued

2021

Author dc:creator

• Yao, Jiangyuan

Advisor dc:contributor.advisor

• Gu, Yongan (Peter)

Committee members dc:contributor.committeemember

• Zeng, Fanhua
• Jia, Na
• Henni, Amr
• Veawab, Amornvadee
• Qing, Hairuo

Language dc:language.iso

en

DOI

https://doi.org/10.82465/4259

OAI identifier oai:identifier

oai:uregina.scholaris.ca:10294/14462