Effects of Pressure and Depressurization Rate of Dissolved CO₂ on the Foaming Characteristics of Crude Oil

Abstract

With the CO 2 flooding technique implemented, much CO 2 gas is dissolved in the produced fluid. A large amount of CO 2 escapes from crude oil due to continual depressurization in the surface pipeline system, leading to massive foam. In this paper, the effects of dissolved-CO 2 pressure and depressurization rate on foaming characteristics were investigated by depressurization. To explore the mechanism in depth, CO 2 solubility and interfacial characteristics were considered. The results indicated that foamability increases as the pressure increases and increases initially and then decreases with an increase in the rate. Further experimental results showed that when the pressure increases from 1.5 to 3.0 MPa at 30 °C, equilibrium interfacial tension decreases only by 12.78%, while CO 2 solubility increases by 81.73%, indicating that CO 2 solubility plays a dominant role in foamability. Additionally, it is inferred that when the rate is lower than 18 L/min, it increases at which point the gas that is originally dissolved inside the crude oil transforms to free gas. When it is increased above 18 L/min, the decrease in the solubility and enhancement of disturbance appear. These may be reasons why foamability decreases. Meanwhile, foam stability, the decay degree of foam height over time, was measured immediately after the foam height reached maximum. It was found that foam stability decreases when the pressure increases and increases initially and then decreases when the rate elevates. Further experimental results indicated that when the pressure increases from 1.5 to 3.0 MPa at 30 °C, the bulk viscosity and interfacial dilational modulus decrease by 23.45 and 38.58%, respectively. It is suggested that the role of interfacial viscoelasticity in foam stability is superior to that of viscosity. Additionally, it was inferred the increased rate below 18 L/min makes bubble size smaller, while the weaker structure of the foam film and higher surface energy make foam stability worse with the rate increased above 18 L/min.

Carbon Dioxide (CO2) Microbubble Suspension and Stabilization for Advancing Tertiary Oil Recovery

“…This relationship between CO 2 flow rate and HLT is significant because it directly impacts the stability and performance of CO 2 foam in EOR applications. Sheng et al reported that the depressurization rate negatively affects CO 2 foam stability, with foam stability decreasing as the rate increases . Similarly, Yan and Zhang highlighted the importance of foam stability, as measured by HLT, in reducing foam mobility within the porous media of oil reservoirs .…”

“…Other factors influencing foam stability include the presence of oil itself, injection velocity, and rock formation characteristics . The interplay between various parameters like pressure, depressurization rate, CO 2 solubility in the oil, and interfacial properties significantly impacts the effectiveness of CO 2 foaming in crude oil systems . Optimizing injection rate, foam quality, and the CO 2 /N 2 ratio is crucial for achieving maximum oil recovery and stable foam .…”

Investigation of the Stability Mechanism of Stimulus-Responsive Wormlike Micelle-CO2 Foams in the Oil Phase

“…At this stage, the research work on stimulus-responsive WLM-CO 2 foam has mainly focused on temperature, concentration, pressure, and response optimization. 25 In explorations of the influence of crude oil on WLMs (mostly with a single hydrocarbon representing crude oil), a gap exists between the construction of the crude oil system and the actual situation. For research on the stimulus-responsive WLM-CO 2 foam system to become systematic, the interaction between crude oil and CO 2 foam must be further explored by dividing crude oil into four components: 26,27 saturated hydrocarbons, aromatic hydrocarbons, resin, and asphaltene.…”

“…At this stage, the research work on stimulus-responsive WLM-CO 2 foam has mainly focused on temperature, concentration, pressure, and response optimization . In explorations of the influence of crude oil on WLMs (mostly with a single hydrocarbon representing crude oil), a gap exists between the construction of the crude oil system and the actual situation.…”