Oil Swelling Research Articles

Experimental study of viscosity reducer-assisted gas huff-n-puff in heavy oil reservoirs

With the diminishing of conventional high-quality oil resources and the advancement of both thermal and non-thermal recovery techniques for heavy oil, the development of heavy and ultra-heavy oil resources is becoming economically feasible. To address some of the reservoir challenges, such as the high heat loss and steam injection costs when using thermal recovery techniques in deep heavy oil reservoirs, as well as the prohibitive cost of CO2 injection when applying non-thermal techniques in heavy oil reservoirs located far from CO2 sources, this study explores the potential application of viscosity reducer-assisted CO2/N2 huff-n-puff (HnP) technique. The effect of different types of gases (N2, CO2 and hybrid N2/CO2) and viscosity reducers is evaluated by analyzing the pressure change, oil recovery rate and oil recovery factor in sandpack models. The results show that 96.62% and 60.75% viscosity reduction is achieved by the water-soluble viscosity reducer ASD-J-202 and the oil-soluble viscosity reducer KR-4, respectively. The oil recovery factors for the hybrid gas and CO2 gas are 17.98% and 18.58%, respectively, in presence of KR-4. In addition, high-quality, stable foamy oil is observed during production coupled with increased formation energy and reduced viscosity. For these runs, the residual oil at the injection end drops to 38.7%. During the soaking stage, N2 dominates the pore space while CO2 gradually diffuses to the distal end, dissolves in the heavy oil, causing oil swelling and increasing the sweep efficiency and oil recovery.

Fracture failure of oil-collecting steel wire reinforced thermoplastic composite pipe

A steel wire-reinforced thermoplastic composite pipe (SRTP) used as an oil connecting experienced fracture failure after 1.8 years’ service. In this paper, we conducted through on-site working condition investigation, visual physical inspection, analysis of the inner lining structure composition, physical and chemical properties analysis, thermal analysis, and mechanical analysis, and morphology analysis. The lining material of the SRTP exhibited significant swelling, which reduced its performance, and operation at high temperatures (>75°C) accelerated this process. Due to the swelling of oil and the permeation of CO2 and H2S, the oil and acid gases penetrated the interlayer of the composite pipe and accumulated in the annular space, continuously corroding and weakening the steel wire. This process gradually reduced its load-bearing capacity and pressure resistance. It is recommended that non-metallic pipes should be selected according to the service conditions to ensure that the materials are consistent with the design requirements.

Chemical enhanced oil recovery from shale‐rich tight carbonate reservoirs using 2‐butoxyethanol as a mutual solvent and diluted seawater

AbstractOil production from tight reservoirs due to their very low permeability and high capillary pressure requires complex operations and materials, so that hydraulic fracturing in these reservoirs is recommended before any chemical injection. This operation turns the reservoir into a fractured one that can produce more oil by activating the imbibition mechanism. The interfacial tension (IFT) of oil and water and reservoir rock wettability as key parameters of overproduction from this type of reservoir can affect this mechanism. In this study, the potential of 2‐butoxyethanol as a mutual solvent for enhanced oil recovery (EOR) was investigated with a focus on the oil production under imbibition in this type of reservoir through performing experiments and calculations of IFT, oil swelling, contact angle, and oil production. The analysis of the results shows that the mechanisms of IFT reduction, wettability alteration, and oil swelling, which all directly affect the oil production under imbibition, reached the desired values using 2‐butoxyethanol in the appropriate concentration along with the dilution of seawater. The lowest values for interfacial tension and contact angle at 0.03 M concentration of the solvent and 5000 ppm salinity at 90°C temperature were 1.315 mN/m and 71.57°, respectively. These values are much lower compared to the values obtained by similar additives, while solvents, unlike 2‐butoxyethanol, are effective in much higher volume ratios. The oil swelling increased by about 14% using 2‐butoxyethanol due to its mass transfer between water and oil phases through the interface. Finally, the oil recovery factors of 42% and 59% were achieved under one‐ and multi‐dimensional spontaneous imbibition (ODSI and MDSI), respectively.

Efficient sealing of cemented sheath: An oil-responsive self-healing latex with toughness enhancement for cement composites

The integrity of the cemented sheath is important to the safe exploration of oil and gas resources. Sealing failure of cement sheath will result in formation fluid channeling and pressure carryover in the annulus. The both toughening and oil-responsive self-healing latex (TOS) was prepared to achieve efficient sealing of cemented sheath, and prolong its service life. The structure and oil swelling behavior of TOS, its toughening and self-healing effects on hardened cement paste (HCP) were analyzed by comprehensive characterizations. Results demonstrated that TOS possessed excellent stability and an oil swelling rate of 1235 %. Cement specimens by curing 28d containing 8 % TOS exhibited a 27.8 % increase in flexural strength, a 48.7 % reduction in elasticity modulus and a 33.8 % reduction in brittleness coefficient. The addition of TOS can effectively improve the toughness of cement. The average pore size of specimens containing 8 % TOS admixture decreased to 9.17 nm. This indicates that TOS enhanced the structural density of cement materials. The crack about 103μm in the cracking specimens with 8 % TOS was almost healed, and the corresponding permeability was reduced 99.1 % after curing in oil. Adsorption and film formation of TOS can resist the cracking of cement sheath, and the oil swelling expansion of film in cement matrix can repair the cracked structure.

Enhanced oil recovery in tight reservoirs by ultrasonic-assisted CO2 flooding: Experimental study and molecular dynamics simulation

CO2-enhanced oil recovery (CO2-EOR) has attracted great attention due to its dual effects of geological carbon storage and economic benefits, but the clay swelling, asphaltene deposition and gas channeling induced by CO2 still restrict its field application. The employment of chemical agents for the purpose of improving CO2-EOR performance is often limited by the heterogeneity of reservoirs and the potential for formation damage. Physical methods, such as ultrasonic-assisted CO2 flooding, appear to offer a promising alternative for CO2-EOR and geological sequestration. This study has conducted oil displacement experiments to investigate the EOR potential of ultrasonic-assisted CO2 flooding in tight reservoirs and clarify the effects of different ultrasound parameters. The ultrasonic waves with 20 kHz of acoustic frequency, 30 W/cm2 of sound intensity, 30 min of sonication time and moderate intermittent working mode can yield violent cavitation effects and avoid undesirable energy dissipation. Nearly a quarter of the saturated crude oil can be recovered from the tight core through ultrasonic-assisted CO2 flooding. It can be attributed to the composition alterations of crude oil and property changes of core matrix. Coupling with ultrasonic waves, CO2 would extract and vaporize crude oil more easily, which promotes oil swelling, lowers oil density and viscosity, decreases oil–gas interfacial tension and thus improves oil recovery. Besides, the ultrasound can help to mitigate the impact of CO2 adsorption-induced clay swelling on pore sizes through fluctuating pressure. And the strong hydrodynamic shear forces generated by mechanical vibration of ultrasound may also help to connect individual small pores and extend micro-fractures. These synergistic effects result in the transformation of micropores into mesopores and macropores. Furthermore, the wettability alteration of core samples implies that the ultrasonic-assisted CO2 flooding can induce the detachment of oil films from the rock surface. Finally, the results of molecular dynamics simulations indicate that the improvement in pressure inside the core sample resulting from ultrasonic cavitation facilitates the mixing of CO2 and oil, thereby weakening gas channeling and improving the displacement efficiency.

Molecular insight into oil displacement by CO2 flooding in water-cut dead-end nanopores.

Understanding the mechanisms underlying residual oil displacement by CO2 flooding is essential for CO2-enhanced oil recovery. This study utilizes molecular dynamics (MD) simulations to investigate the displacement of residual oil by CO2 flooding in dead-end nanopores, focusing specifically on the water-blocking effect. The findings reveal that oil displacement does not commence until the water film is breached. The dissolution of CO2 molecules in water and the hydrogen bond interactions between water and rock are the primary factors that disrupt the hydrogen bond network among the water molecules, facilitating the breakthrough of the water film. Additionally, the displacement process can be delineated into four distinct stages - encompassing water film rupture, oil swelling, massive oil displacement, and displacement completion - as evidenced by the oil recovery-displacement time curves. Moreover, a cutting-edge oil recovery-displacement time model precisely quantifies crucial stages in the displacement process. For example, when t < δ, trapped oil is impeded by the water film, while when t > δ + 3τ, displacement culminates successfully. Altogether, this research bolsters comprehension of residual oil displacement in the presence of water blocking and advocates for sustainable oil production strategies in oilfields.

Molecular Insights into Soaking in Hybrid N2-CO2 Huff-n-Puff: A Case Study of a Single Quartz Nanopore-Hydrocarbon System.

Hybrid N2-CO2 huff-n-puff (HnP) has been experimentally demonstrated to be a promising approach for improving oil recovery from tight/ultratight shale oil reservoirs. Despite this, the detailed soaking process and interaction mechanisms remain unclear. Adopting molecular dynamic simulations, the soaking behavior of hybrid N2-CO2 HnP was investigated at the molecular and atomic levels. Initially, the soaking process of fluid pressure equilibrium after injection pressure decays in a single matrix nanopore connected to a shale oil reservoir is studied. The study revealed that counter-current and cocurrent displacement processes exist during the CO2 and hybrid N2-CO2 soaking, but cocurrent displacement occurs much later than counter-current displacement. Although the total displacement efficiency of the hybrid N2-CO2 soaking system is lower than that of the CO2 soaking system, the cocurrent displacement initiates earlier in the hybrid N2-CO2 soaking system than in the CO2 soaking system. Moreover, the N2 soaking process is characterized by only counter-current displacement. Next, the soaking process of fluid pressure nonequilibrium before the injection pressure decays is investigated. It was discovered that counter-current and cocurrent displacement processes initiate simultaneously during the CO2, N2, and hybrid N2-CO2 soaking process, but cocurrent displacement exerts a dominant influence. During the CO2 soaking process, many hydrocarbon molecules in the nanopore are dissolved in CO2 while simultaneously exhibiting a substantial retention effect in the nanopore. After pure N2 injection, there is a tendency to form a favorable path of N2 through the oil phase. The injection of hybrid CO2-N2 facilitates the most significant cocurrent displacement effect and the reduction in residual oil retained in the nanopore during the soaking process, thus resulting in the best oil recovery. However, the increase rate in total displacement efficiencies of the different soaking systems over time (especially the hybrid N2-CO2 soaking system) was significantly larger before than after injection pressure decays. Additionally, the displacement effect induced by oil volume swelling is significantly restricted before the injection pressure decays compared to the soaking process after the injection pressure decays. This study explains the role of CO2-induced oil swelling and N2-induced elastic energy played by hybrid N2 and CO2 at different stages of the hybrid N2-CO2 soaking process before and after pressure decays and provides theoretical insights for hybrid gas HnP-enhanced recovery. These pore-scale results highlight the importance of injection pressure and medium composition during the soaking process in unconventional oil reservoirs.

Optimizing oil recovery with CO2 microbubbles: A study of gas composition

Microbubbles represent a feasible method for enhancing oil recovery (EOR). To further investigate microbubble displacement and interaction mechanisms between gas and oil, in this study, EOR experiments were conducted on normal (NB) and microbubble (MB) CO2 and CO2–N2 mixtures using NMR. The CO2 flooding process and the mechanism of microbubble CO2-oil interaction were examined, the contributions of small and large pores to oil recovery and CO2 storage were quantified. Importantly, economic benefits were analyzed under different injection conditions for the first time. The results show CO2 injection formed a stable displacement front and the maximum oil recovery was obtained from MB CO2. The oil swelling and “jamin effect” increased MB CO2 sweep area and the efficiency of small pore utilization was 20.9 % higher than NB CO2. Compared to CO2 injection, the oil recovery gradually decreased with increasing N2 concentration due to the reduced sweep area. The maximum CO2 storage efficiency achieved under MB CO2 injection was 35.92 %. Economic analysis revealed that MB CO2-EOR could provide significant economic benefits of approximately US $492.5 per ton of CO2 injected. This study provides data for the commercial application of microbubble technology.

Investigation on storage stability, H2S emission and rheological properties of modified asphalt with different pretreated waste rubber powder

The use of waste rubber powder (WRP) to produce WRP modified asphalt (WRMA) has been proved to have wide application prospects, however, WRMA has poor storage stability and is prone to release H2S and other toxic fumes. Therefore, the one-step method to ameliorate these two problems through pretreating WRP was proposed, and the microwave activation, waste cooking oil (WCO) swelling and acid or alkali solution soaking were applied to pretreat WRP in this study, respectively. The scanning electron microscope and infrared spectroscopy were selected to analyze the microstructures and functional groups of different pretreated WRP. The fluorescence microscopy and hot tube test were employed to evaluate the compatibility of pretreated WRP with asphalt. The H2S gas detector and gas chromatography-mass spectrometry were introduced to research the flue gas emissions of pretreated WRP and prepared WRMA. The experimental results show that the microstructure and functional groups of the pretreated WRP are greatly changed and its surface activity is increased. The storage stability of WRMA prepared with pretreated WRP is obviously improved, and the optimized result is obtained with the microwave/WCO composite treatment, with a segregation index reduction of 40.91%. Also, the pretreatment of WRP does reduce H2S and flue gas emissions. The cumulative H2S concentration reduction of WRP after NaOH solution soaked reaches 32.14% at 30 min, and the total flue gas concentration reduction of the prepared WRMA reaches 21.54%. The results could offer guidance for the clean utilization of WRP, the efficient storage of WRMA and the effective suppression of its flue gas.

Factors Influencing the Rheology of Methane Foam for Gas Mobility Control in High-Temperature, Proppant-Fractured Reservoirs

Gas-enhanced oil recovery (EOR) through huff-n-puff (HnP) is an important method of recovering oil from fracture-stimulated reservoirs. HnP productivity is hampered by fracture channeling, leading to early gas breakthroughs and gas losses. To mitigate these issues, foam-generating surfactants have been developed as a method of reducing injected gas phase mobility and increasing oil recovery. This work investigates foam generation and propagation by a proprietary surfactant blend in high-temperature, high-pressure, high-permeability, and high-shear conditions that simulate the environment of a proppant-packed fracture. Bulk foam tests confirmed the aqueous stability and foaming viability of the surfactant at the proposed conditions. Through several series of floods co-injecting methane gas and the surfactant solution through a proppant pack at residual oil saturation, the effects of several injection parameters on apparent foam viscosity were investigated. The foam exhibited an exceptionally high transition foam quality (&gt;95%) and strong shear-thinning behavior. The foam viscosity also linearly decreased with increasing pressure. Another flood series conducted in an oil-free proppant pack showed that swelling of residual oil had no effect on the apparent foam viscosity and was not the reason for the inversely linear pressure dependency. An additional flood series with nitrogen as the injection gas was completed to see if the hydrophobic attraction between the methane and surfactant tail was responsible for the observed pressure trend, but the trend persisted even with nitrogen. In a previous study, the dependence of foam viscosity on pressure was found to be much weaker with a different foaming surfactant under similar conditions. Thus, a better understanding of this important phenomenon requires additional tests with a focus on the effect of pressure on interfacial surfactant adsorption.

Methane Huff-n-Puff in Eagle Ford Shale – An Experimental and Modelling Study

Injection pressure, soaking duration, and depletion strategy are crucial operational parameters for a successful gas Huff-n-Puff (HnP) pilot. There is limited experimental data on efficiency of natural gas (C1) HnP, particularly in the Eagle Ford Formation. This study aims to optimize this technique using an organic shale sample from this formation. We use a state-of-the-art visualization cell for real-time monitoring of gas-oil interactions under 1) bulk-phase and 2) core HnP conditions to investigate synergy between these two experiments. We consider two injection pressures of 22.55 and 36 MPa with soaking durations of 200 and 480 h to assess their impact on gas diffusion in oil. We develop a mathematical scaling technique that incorporates HnP field data to select appropriate depletion strategies for lab-scale experiments. We adopt a hybrid depletion strategy consisting of fast and slow depletions. We estimate bulk-phase and apparent diffusion coefficients of C1 in oil and quantify the tortuosity of the shale sample. Compositional analysis reveals key oil-recovery mechanisms, including solution-gas drive, oil swelling, and oil vaporization. Longer soaking intervals result in more gas diffusion into the core under both pressure conditions, with higher injection pressure leading to more diffused gas. Bulk-phase and apparent diffusion coefficients are on the order of 10-8 and 10-10 m2/s, respectively, with an average tortuosity of 1.66. Both coefficients decrease by increasing pressure due to suppressed gas mobility. Compositional data reveals the extraction of C5 to C9 oil components through the oil vaporization mechanism, with minimal pressure impact on the composition of extracted oil. Following a single-cycle C1 HnP, ultimate oil recovery factors range from 27.9 to 46.1 % of the initial oil-in-place, with recovery increasing with higher pressure and longer soaking durations.

Multiphase Multicomponent Transport Modeling of Cyclic Solvent Injection in Shale Reservoirs

Summary A thorough understanding of fluid transport in ultratight shale reservoirs is crucial for designing and optimizing cyclic solvent injection processes, known as huff ’n’ puff (HnP). We develop a two-phase multicomponent numerical model to investigate hydrocarbon and solvent transport and species mixing during HnP. Unlike the conventional modeling approaches that rely on bulk fluid (advective) transport frameworks, the proposed model considers species transport within nanopores. The chemical potential gradient is considered the driving force for the movement of nonideal fluid mixtures. A binary friction concept is adopted that considers friction between different fluid molecules and between fluid molecules and pore walls. After validating the developed model against analytical solutions and experimental data, the model examines solvent HnP enhanced oil recovery (EOR) mechanisms by considering four-component oil and Eagle Ford crude oil systems. The impacts of injection pressure, primary production duration, soaking time, and solvent type on the oil recovery are examined. The results reveal that the formation of a solvent-oil mixing zone during the huff period and oil swelling and vaporization of oil components during the puff period are key mechanisms for enhancing oil recovery. Furthermore, the incremental recovery factor (RF) increases with injection pressure, even when the injection pressure exceeds the minimum miscibility pressure (MMP), implying that MMP may not play a critical role in the design of HnP in ultratight reservoirs. The results suggest that injecting solvents after a sufficient primary production period is more effective, allowing reservoir pressure depletion. Injecting the solvent without enough primary production may result in significant production of the injected solvent. The results show that the solvent-oil mixing zone expands, and the solvent recycling ratio decreases as soaking time increases. However, short soaking periods with higher HnP cycles are recommended for improving oil recovery at a given time frame. Finally, CO2 HnP outperforms CH4 or N2 HnP due to the higher ability of CO2 to extract a larger amount of intermediate and heavy components into the vapor phase, which has higher transmissibilities as compared with the liquid phase.

Automated control of thermal vacuum impregnation and swelling of oil- and gasoline-resistant elastomers

Polymeric materials used in the rolling stock are currently subject to increased requirements for durability. We present a method for accelerated and automated rapid analysis of the impregnation of polymeric materials used in various aggressive environments to determine their service life as sealing products. The results of studying changes in the physical and mechanical properties of samples are given on the example of elastomeric materials used as separating and sealing materials made of oil- and petrol resistant rubber MBS-S. Hydrocarbons based on mineral oil products with different viscosity coefficients were used as working media. It is shown that the time of impregnation of the MBS-S polymer, spent on testing according to the standard method, exceeds more than 10 times the standard terms rated for repair and maintenance. Tests using the developed express filling unit showed a reduction of the impregnation time to a level acceptable in production. The derived mathematical dependences for the process of filling MBS-S oil and petrol resistant rubber with a standard working fluid and automation of filling control make it possible to predict changes in the resistance of polymeric materials. The results obtained can be used in developing database of the swelling dynamics for various materials and predicting the service life of polymers in an aggressive environment of various etiology.

Phytochemical, physical and functional properties of flour blends produced from wheat, unripe plantain and pigeon pea

This study investigated the phytochemical, physical and functional properties of flour blends produced from wheat, unripe plantain and pigeon pea, suitable for purposes of formulating food composition table for the flour blends by homogenously mixing wheat, pigeon pea and unripe plantain flour in the proportion of wheat flour (100%) 100:0 (WHF), wheat-pigeon pea flour 95;5:0 (WPF),wheat-unripe plantain-pigeon pea flour 85:10.5 (WPU1), wheat-unripe plantain-pigeon pea flour 75:15:10 (WPU2)and 65:20:15 (WPU3) respectively. WHF represent 100% wheat flour served as control. There was a significant difference (p&lt;0.05) among samples of flour blends (WHF), (WPF),(WPU1), (WPU2) and (WPU3).The results obtained for proximate composition, phytochemical and functional analysis ranged: crude fiber (2.90-4.07%), protein (10.10-14.50%), moisture (5.00-10.50%), ash (0.50-0.7%), fat (2.04-3.50%), carbohydrate(67.95-79.26%), saponins (0.46-2.97 mg/100g), flavonoids (4.50-4.70 mg/100g), tannins(0.80-1.26 mg/100g) phenols (1.00-1.50 mg/100g), bulk densities (0.41-8.20g/cm3), emulsion capacity (9.20-5.20%), foaming capacity (2.90-10.60%), water absorption capacity (6.20-6.60g/g), oil absorption capacity (0.10-8.50%) and swelling capacity (25.00-29.00%) respectively. The results showed that incorporation of pigeon pea flour into wheat flour significantly (p&gt;0.05) increased the protein, fibre and fat content of composite flour. As the ratio of wheat decreases and increase in the unripe plantain and pigeon pea, the carbohydrate content decreases significantly. WHF shows higher carbohydrate content among samples. This is evident that wheat has high carbohydrate content. Based, on the result from this study, it can be concluded that flour formulation from different four blends can improve the nutritional values of flour blends and reduce anti-nutrients drastically.

The impacts of CO2 flooding on crude oil stability and recovery performance

Numerous studies have investigated the fundamental mechanisms by which CO2 flooding can increase oil production by altering the properties of the hydrocarbon fluid, including oil swelling, viscosity and interfacial tension reductions, and the extraction of light-to-intermediate components. However, the interactions between CO2 and hydrocarbon fluid may also cause several problems, such as asphaltene precipitation due to crude oil's instability during the CO2 flooding process. This study investigates the complex factors that affect the instability of crude oil, including CO2 injection pressures, temperatures, and crude oil compositions. The light-dead oil samples taken from two Indonesian oil fields were used. The impacts of the instability of crude oil on CO2 displacement performance were also observed to evaluate oil recovery and minimum miscibility pressure (MMP). The observation was performed using a slim tube under varying CO2 high-pressure injections at 90 °C and 70 °C. The produced oils were analyzed based on their polarity component, saturates, aromatics, resins, and asphaltenes fractions, to observe the changes in oil composition and colloidal index instability. The results showed that increasing temperatures at given pressures resulted in higher oil recovery. Moreover, the asphaltene and resin fractions in the oil produced at a lower temperature significantly decrease compared to those at a higher temperature. It was also shown that asphaltene tends to precipitate more easily at a lower temperature. The other phenomenon revealed that the lighter oil resulted in a lower recovery than the heavier oil at a given pressure and temperature and correspondingly higher MMP. It was also suggested that CO2 flooding is more likely to cause asphaltene precipitation in light oils.

An experimental assessment of seawater alternating near-miscible CO2 for EOR in pre-salt carbonate reservoirs

Enhanced oil recovery (EOR) methods considering the injection of seawater and CO2 have been widely investigated and applied in the Brazilian pre-salt fields. The high availability of these fluids in offshore facilities makes seawater alternating CO2 (CO2WAG) a viable and environmentally friendly EOR method. It combines the advantages of seawater injection and CO2 injection to improve fluid mobility control and viscous fingering attenuation. In this study, in addition to the core flooding test of secondary seawater flooding and the tertiary CO2WAG, different experimental determinations provided a better understanding of the mechanisms related to the EOR methods applied to a carbonate core composed mainly of dolomite, and their interactions with pre-salt oil, brines and CO2. A 13.30% incremental oil recovery was achieved by alternating seawater with CO2. Considering formation brine, non-carbonated seawater, or seawater saturated with CO2, contact angle measurements revealed that the wettability alteration is not significant when dolomite is slightly water-wet, even in the presence of CO2. On the other hand, measures of brine/oil, brine/CO2/oil and CO2/oil interfacial tension emphasize the beneficial effects of this gas for EOR, in near-miscible conditions. This is achieved by the reduction of capillary and interfacial forces that act by trapping the oil in the pores of the medium. The brine salinity, the presence of magnesium in dolomite and the oil's low TAN/TBN ratio proved to be essential factors in determining the slightly water-wet wettability of the dolomitic rock and the interfacial tension between the phases. Furthermore, for the experiments carried out in the presence of brine with solubilized CO2, a considerable variation in the oil drop volume was observed due to the mass transfer of CO2 between the phases. Finally, experimental results showed that the additional oil recovery was mainly associated with oil swelling, viscosity reduction, and mobility increase, which occur even in near-miscible conditions during CO2WAG.

Microfluidic investigation on asphaltene interfaces attempts to carbon sequestration and leakage: Oil-CO2 phase interaction characteristics at ultrahigh temperature and pressure

CO2 huff-n-puff is a potential approach to improve the oil displacement efficiency in the deep reservoirs, which can achieve carbon sequestration and efficient oil production, simultaneously. However, the fundamental understanding of carbon mass transport, sequestration and leakage mechanism in deep geological reservoirs at the microscopic pore scale is still ambiguous. In this work, we innovatively designed a precise CO2 huff-n-puff microfluidic experiment under ultrahigh temperature and pressure conditions (55 MPa, 115 °C) to study the microscopic mechanism of CO2 utilization, storage and leakage (CUSL) in pore scale. Moreover, we proposed the quantitative analysis method for oil-CO2 interaction behavior to explicit dissolution and extraction characteristics, pressure threshold and interface stability by introducing Pseudo-Color algorithm and relevant parameters such as dynamic oil swelling factor, contact angle and gray value. Then, the pore-scale dynamics of the fluid interaction mechanism during the soak and puff process were quantitatively characterized, corresponding to the carbon sequestration efficiency of crude oil continuously exposed to scCO2 and the leakage risk with step-down production, respectively. The experimental results indicate that during the huff process, the oil-CO2 phase behavior characteristics at 115 °C can be divided into swelling, immiscible extraction and miscible extraction regions, which are coordinately controlled by dissolution mechanism, capillary effect and vaporization mechanism. Moreover, ultrahigh temperature oil generally requires higher pressure to start extraction and miscibility (Pext = 6.38 and 15.96 MPa, MMP = 9.71 and 23.73 MPa, T = 50 and 115 °C, respectively), while the asphaltene precipitation pressure Pasp is lower. At ultrahigh temperatures, the oil-CO2 interaction also enters the contact angle fluctuation region in advance, and the morphology of asphaltene particles is single, fine and uniform. When the soaking time is 36 min, the non-extractable oil component gradually evolves into a carbon sequestration interface. During the subsequent puff process, the more stable the carbon sequestration interface in the smaller blind end, the lower the leakage risk, corresponding to the leakage pressure difference of up to 40.93 MPa. This work has important practical significance for deep resource extraction and CUSL industrial application.

Determination of Concentration-Dependent Effective Diffusivity of Each Gas Component of a Binary Mixture in Porous Media Saturated with Heavy Oil under Reservoir Conditions

Summary One frequently used enhanced heavy oil recovery technique is gas injection, during which heavy oil viscosity is reduced due to diffusion of gaseous components and heavy oil swelling in porous media. Effective diffusivities of gas components are generally assumed to be constants, while no attempts have been made to determine both the concentration-dependent effective diffusivity in porous media saturated with heavy oil and the preferential contribution of each component in a binary/ternary gas mixture. In this study, a pragmatic and robust technique has been proposed to determine the concentration-dependent effective diffusivity of each gas component by reproducing the experimental measurements during pressure decay tests for CO2-C3H8-heavy oil systems in porous media. Experimentally, CO2 and C3H8 are utilized to diffuse into sandpacks fully saturated with heavy oil. Under a constant temperature within a thermostatic chamber, the pressures of the aforementioned gas(es)-heavy oil systems are consistently tracked and saved while gas samples are taken at the start and end of the diffusion tests for gas chromatography analyses. Theoretically, a mass transfer model is formulated to determine effective gas diffusivity in heavy oil as a concentration-dependent function by incorporating Fick’s second law and the modified Peng-Robinson equation of state (PR EOS). The concentration-dependent effective diffusivity for each gas component is ascertained when the measured pressure profiles and gas compositions are matched well to their correspondingly calculated values with minimum deviations. Compared to either a constant assumption or a linear concentration-dependent relation with respect to diffusivity, an exponential concentration-dependent relation leads to more accurately reproducing the measured pressure profiles. Compared with pure CO2, its effective diffusivity in a binary (i.e., CO2 and C3H8) gas system is found to be larger, indicating that C3H8 accelerates the CO2 mass transfer into heavy oil under the same circumstances. Furthermore, this study confirms that a larger tortuosity of a porous medium leads to a longer diffusion path with less contact between gas and liquid phases and that a lower concentration of a gaseous component yields a lower effective diffusivity.

Evaluation of xanthan gum and ascorbic acid in the physicochemical properties of bean/corn flour and pound cake

This work aimed to evaluate the effect of xanthan gum and ascorbic acid on the techno-functional properties of bean/corn composite flour for producing and evaluating a pound cake. The composite flours were formulated with bean flour (80%) and nixtamalized corn flour (20%) using xanthan gum and/or ascorbic acid in different concentrations (0, 0.25 and 0.50%). The different flours composed of beans/corn were evaluated for their water absorption capacity (2.68 to 3.84 g/g), oil absorption capacity (1.14 to 1.43 g/mL) and swelling capacity (10.57 to 10.98 mL/g). The different flours composed of beans/corn were used for the production of pound cakes. As the content of xanthan gum and/or ascorbic acid increased, the different pound cakes presented better weight, volume and volume index. Likewise, the nutritional quality of the pound cake is improved, compared to the flour used individually.

Evaluation of proximate composition, functional and pasting properties of millet-based breakfast cereals supplemented with soybean and date fruit flours

This study was designed to evaluate the proximate composition, functional and pasting properties of breakfast cereals produced from blends of millet, soybean and date fruit flour. Soybeans and date fruits were separately processed into flours and used at varying replacement levels (5-30% soybean and 5-20% date fruit) for malted millet flour in the production of breakfast cereals with breakfast cereal produced from 100% malted millet flour as control. The proximate composition, functional and pasting properties of the breakfast cereals were determined using standard methods. The moisture, crude protein, fat, crude fibre and ash contents of the breakfast cereals increased significantly (p&lt;0.05) with increase in substitution of soybean and date fruit flours from 7.19-7.63%, 7.69-18.32%, 3.09-4.03%, 2.47-3.86% and 1.21-2.07, respectively, while the carbohydrate and energy contents decreased from 78.37-64.13% and 371.99-365.10KJ/100g, respectively. The functional properties (bulk density, water absorption capacity, oil absorption capacity, solubility index, swelling and gelation capacities) of the samples increased significantly (p&lt;0.05) with increase in substitution of soybean and date fruit flours from 0.36-1.55g/cm3, 43.54-86.54ml/g, 57.36-91.76ml/g, 76.72-132.72%, 1.55-2.14g/g and 1.32-1.72g/g, respectively. The pasting properties of the samples also showed that the peak viscosity, trough viscosity, final viscosity, peak time and pasting temperature increased as the levels of addition of soybean and date fruit flours increased in the products, while their breakdown and setback viscosities decreased. The study showed that the proximate composition, functional and pasting properties of millet‑based breakfast cereals could be improved by supplementing millet flour with different proportions of soybean and date fruit flours in the preparation of good quality breakfast cereal products.