Capturing the Dynamics of Foam Coarsening in a HPHT Microfluidic System

The foam coarsening process is significant to foam stability in porous media. This study provides, for the first time, direct visualization of the foam coarsening process in porous media under realistic reservoir conditions. Foam coarsening behavior in porous media has shown a similar linear increase in the average bubble area to that in an open system but differs in two stages. The average bubble area increases with a faster rate in stage 1 and then increases with a slower rate in stage 2 and stage 2 dominates the foam coarsening process. The transition between the two stages occurs as the inner bubbles disappear when the edge bubbles start feeling the effects of the walls. The foam at steady-state shows a bimodal size distribution with bubbles trapped in the pore bodies and pore throats. The effects of pore pressure (600-3200 psi) and temperature (22-100 °C) were studied. Foam coarsening dynamics are sensitive to pore pressure and temperature, where higher pore pressure and lower temperature are more favorable to maintain a stable foam. Finally, the coarsening rates of foams generated with different gas phases were compared. In contrast to N2 foam and gas CO2 foam, supercritical CO2 foam exhibits the slowest coarsening rate because of its ultralow interfacial tension.

Novel CO2/N2 Foam Concept and Optimization Scheme for Improving CO2-foam EOR Process

Nitrogen and Carbon dioxide are the most common gases utilized in enhanced oil recovery (EOR) techniques. Most of the gas injection process suffers from the gravity override and viscous fingering resulting in lower oil recovery. Foam is introduced in enhanced oil recovery (EOR) to mitigate these problems encountered during gas flooding. When it comes to the CO2-gas injection the CO2-becomes supercritical at a typical reservoir condition giving it difficulty to form CO2-foam at reservoir condition. The CO2-foam has a common problem to become weaker above its supercritical conditions of 1100 psi and 31°C. As a result, the advantages of using CO2 foam are diminished due to the weakness of CO2-foam at supercritical conditions and results in a lower recovery. However, CO2-foam can be generated by replacing a portion of CO2 with N2 gas. It lacks the understating of mixture properties and its effect on EOR. This study evaluates the performance of CO2/N2 foam at supercritical conditions for EOR. It aims to improve recovery under supercritical conditions by using N2/CO2 mixture foam and optimize the foam quality and CO2/N2 ratio. The results from the experiments showed that the CO2/N2 foam flooding recovered an additional oil of Original Initial Oil in Place (OIIP) indicating that foam flooding succeeded in producing more oil than pure CO2-foam injection processes. Also, the results of foam flooding at different foam quality and CO2/N2 ratio significantly affected the performance and recovery of the process. Hence it is necessary to optimize the CO2/N2 foam parameters flooding process which is affected by the parameters such as foam quality and CO2/N2 ratio. The study also shows an experimental approach for optimizing CO2/N2 foam parameters. The concept of adding N2 to CO2 is a novel way of generating CO2 foam at supercritical conditions. Although investigators are trying different ways to generate the strong and stable CO2- foam, adding N2 to CO2 can be considered to be the easiest way for foam generation as CO2 is always having some impurities in the form of other gases and N2 can be considered as one of such gas helps in generating the foam.

Machine Learning Application to CO2 Foam Rheology

Conventional foam modelling techniques require tuning of too many parameters and long computational time in order to provide accurate predictions. Therefore, there is a need for alternative methodologies for the efficient and reliable prediction of the foams’ performance. Foams are susceptible to various operational conditions and reservoir parameters. This research aims to apply machine learning (ML) algorithms to experimental data in order to correlate important affecting parameters to foam rheology. In this way, optimum operational conditions for CO2 foam enhanced oil recovery (EOR) can be determined. In order to achieve that, five different ML algorithms were applied to experimental rheology data from various experimental studies. It was concluded that the Gradient Boosting (GB) algorithm could successfully fit the training data and give the most accurate predictions for unknown cases.

Supercritical CO2-Foam Screening and Performance Evaluation for CO2 Storage Improvement in Sandstone and Carbonate Formations

Injecting carbon dioxide (CO2) as foam during enhanced oil recovery (EOR) can improve injectate mobility and increase sweep efficiency. Integrating CO2-foam techniques with carbon capture, utilization and storage (CCUS) operations is of recent interest, as the mobility control and sweep efficiency increases seen in EOR could also benefit CO2 storage during CCUS. In this study, a variety of different charge, hydrocarbon chain length, head group surfactants were evaluated by surface tension, bulk and dynamic CO2-foam performance assessments for CCUS. The optimal foam candidate was expected to provide satisfying mobility control effects under reservoir conditions, leading to an improved water displacement efficiency during CO2-foam flooding that favors a more significant CO2 storage potential. All tested surfactants were able to lower their surface tensions against scCO2 by 4-5 times, enlarging the surface area of solution/gas contact; therefore, more CO2 could be trapped in the foam system. A zwitterionic surfactant was found to have slightly higher surface tension against CO2 while exhibiting the highest foaming ability and the most prolonged foam stability with a relatively slower drainage rate among all tested surfactants. The dynamic performance of scCO2-foam stabilized by this zwitterionic surfactant was also evaluated in sandstone and carbonate cores at 13.79 MPa and 90°C. The results show that the mobility control development in carbonate core was relatively slower, suggesting a gradual foam generation process attributed to the higher permeability than the case in sandstone core. A more significant cumulative CO2 storage potential improvement, quantified based on the water production, was recorded in sandstone (53%) over the carbonate (47%). Overall, the selected foam has successfully developed CO2 mobility control and improved water displacement in the occurrence of in-situ foam generation, hence promoting the storage capacity for the injected CO2. This work has optimized the foaming agent selection method at the actual reservoir conditions and evaluated the scCO2-foam performance in establishing high flow resistance and improving the CO2 storage capacity, which benefits integrated CCUS studies or projects utilizing CO2-foam techniques.

Visualizing and Quantifying Generation, Propagation, and Sweep of Nanocellulose-Strengthened Carbon Dioxide Foam in a Complex 2D Heterogeneous Fracture Network Model

Summary There exist two main issues hampering the wide application and development of carbon dioxide (CO2) foam in conformance improvement and CO2 mobility reduction in fractured systems: (1) instability of foam film under reservoir conditions and (2) uncertainties of foam flow in complex fractures. To address these two issues, we previously developed a series of nanocellulose-strengthened CO2 foam (referred to as NCF-st-CO2 foam), while the primary goal of this work is to thoroughly elucidate generation, propagation, and sweep of NCF-st-CO2 foam in a visual 2D heterogeneous fracture network model. NCF-st-CO2 foam outperformed CO2 foam in reducing gas mobility during either coinjection (COI) or surfactant-alternating-gas (SAG) injection, and the threshold foam quality was approximately 0.67. Foam creation was increased with the total superficial velocity for CO2 foam and almost stayed constant for NCF-st-CO2 foam in fractures during COI. For SAG, large surfactant slug could prevent CO2 from early breakthrough and facilitate foaming in situ. The improved sweep efficiency induced by NCF-st-CO2 foam occurred near the producer for both COI and SAG. Film division and behind mainly led to foam generation in the fracture model. Gravity segregation and override was insignificant during COI but became noticeable during SAG, which caused the sweep efficiency decrease by 3 to 9%. Owing to the enhanced film, NCF-st-CO2 foam enabled mitigation of the gravitational effect, especially around the producer.

Storage of CO2 and Coal Fly Ash using Pickering Foam for Enhanced Oil Recovery

CO2 foams have been used for a long time for enhanced oil recovery (EOR) and carbon capture, utilization, and storage. Note that conventional CO2 foam focuses on mobility control and storage of bare CO2. However, this technology has suffered from low storage efficiency and EOR because of foam instability. In this study, the geological storage of CO2 and coal fly ash (CFA) using Pickering foam for EOR was explored. The aim is to obtain an inexpensive method for EOR and storage of greenhouse gases and atmospheric pollutants. The Pickering foam was prepared using Waring blender method. The experiments were conducted to evaluate CO2/liquid interface enhancement by measuring the interfacial tension and interfacial viscoelastic modulus. As per the heterogeneous sandpack flooding experiments, the profile control capacity and the performance of oil displacement using CO2 foam enhanced by CFA were investigated. The amount of storage from dynamic aspects of CO2 and CFA was measured to demonstrate the storage law. The stability of aqueous foam was improved significantly after the addition of CFA. The half-life time of foam stabilized by CFA particles increased by more than about 11 times than that of foam without CFA particles. The interfacial dilatational viscoelastic modulus of CO2/foaming solution increased with CFA particle concentration increasing, indicating the interface transformed from liquid-like to solid-like. Flooding experiments in heterogeneous porous media showed that more produced fluid was displaced from the relatively low-permeability sandpack after the injection of CO2 foam with CFA. The oil recovery by CFA stabilized foam was improved by ~28.3% than that of foam without CFA particles. And the sequestration of CO2 in heterogeneous porous media was enhanced with the addition of CFA to CO2 foam, and the CFA stabilized foam displayed a strong resistance to water erosion for the storage of CO2 and CFA. This work introduces a win–win method for EOR and storage of CO2 and atmospheric pollutant particles. CFA from coal combustion was used as an enhancer for CO2 foam, which improved the interfacial dilatational viscoelasticity of foam film and the dynamic storage of CO2. Furthermore, the storage of CO2 and CFA contributed to improvement in sweep efficiency, and thus EOR.