Imbibition Time Research Articles

The influence mechanism and the contribution of capillary force and gravity to recovery in spontaneous imbibition in low permeability reservoirs

Spontaneous imbibition is one of the important means to enhance oil recovery in low permeability reservoirs, and it has good field application effects. Through the interfacial tension (IFT), contact angle (CA), and adsorption experiments, the effects of SDBS surfactant on IFT and reservoir wettability were studied, and the adsorption rule of SDBS at the mineral surface was obtained. On this basis, the imbibition recovery and mechanism of cores with different permeability are studied. The study showed that in low permeability reservoir, gravity and capillary force are the main controlling factors of imbibition. In the early stage, gravity determines the recovery, because the imbibition rate is 2.75 times that dominated by capillary force. The capillary force can continue to produce oil in small pores, and the imbibition time is twice that of gravity, which determines the recovery in the late imbibition stage. Therefore, the synergistic effect of gravity and capillary force can optimize the imbibition recovery, in low permeability reservoirs. When the concentration of SDBS solution is CMC (0.1%), due to the mineral interface adsorbs, the capillary force decreases by 10.76%, and the adhesion work increases by 3.42 times, resulting in a decrease in the imbibition recovery. The imbibition driving force is different for different reservoir properties, which can be adjusted by adding a surfactant to change IFT and CA.

Understanding Imbibition Mechanisms of Catanionic Surfactant–Stabilized Nanoemulsion for Enhanced Oil Recovery in Tight Sandstone Reservoirs: Experimental and Numerical Assessment

Summary Surfactant-induced imbibition is considered a promising method for increasing oil recovery from tight oil reservoirs beyond primary production. Nanoemulsion (nE) offers a great potential for this application owing to its unique physicochemical properties, such as kinetic stability, large surface area, and low oil-aqueous interfacial tension (IFT). Herein, we designed and prepared a series of surfactant-stabilized oil-in-water (O/W) nE using efficient catanionic surfactants by a low-energy method. The physicochemical properties of the nE samples were comprehensively characterized to better perform experimental and numerical simulations and constrain the modeling. We conducted imbibition tests on Chang 7 tight cores using nE and brine and also assessed the imbibition dynamics. Results indicated that nE was successfully synthesized at a surfactant concentration ranging from 0.4 to 1.0 wt%. The oil droplets in nE had a mean size of 10 nm. All the nE samples were able to lower the oil-aqueous IFT to an ultralow level of 10–3 mN/m. In addition, nE demonstrated superior capacities in wettability alteration, and oil solubilization and emulsification, which were all integrated into numerical modeling. The imbibition oil recovery was increased by 18.8% of the initial oil in place when nE1 (0.4 wt%) was used compared to that of brine. Because of the interactions among oil, nE, and rock surface, nE required a longer time to reach imbibition equilibrium than brine. The simulation results, for the first time, suggested that the dominant imbibition mechanisms of nE varied with time, during which IFT reduction and wettability alteration played the leading roles in the first 50 hours. The reactions of oil solubilization and emulsification became significant after 50 hours and then contributed equally to the oil recovery with IFT reduction and wettability alteration. The diffusion of nanosized oil droplets increased the equilibrium time of imbibition, thereby promoting the ultimate oil recovery.

THE FRACTAL MATHEMATICAL MODELS FOR SPONTANEOUS AND FORCED IMBIBITION WITH DIFFERENT CROSS-SECTION SHAPES IN SHALE OIL RESERVOIR

Large-scale hydraulic fracturing is the critical technology for effective shale oil production. However, the imbibition flow mechanisms of fracturing fluid in shale micropores and the influence of shale microstructure and physical properties are still indistinct, which makes the optimization goal of fracturing flowback unclear and restricts the enhancement of shale oil recovery. Therefore, based on SEM and XRD experiments, it is analyzed that shale has the characteristics of multiple pores, which are divided into organic pores, brittle mineral pores, and clay pores. Nonetheless, how the tube cross-section controls the interface displacement is not well discussed in the available literature, especially in irregular triangles, rectangles and other non-circular shapes. This paper studies the influence of cross-section shapes on the capillary force by considering the corner flow of the wetting phase, and it analyzes the imbibition dynamics of different types of pores. Using the shale multi-pores physical model and fractal theory, the shale semi-analytical solution models of SI and FI are established. Theoretical analysis of the water imbibition mechanisms shows that the key factors controlling SI and FI volume include imbibition time, fluid properties, pore cross-section shapes, tortuosity, and forced pressure.

A NOVEL FRACTAL MODEL FOR SPONTANEOUS IMBIBITION IN DAMAGED TREE-LIKE BRANCHING NETWORKS

Spontaneous imbibition has attracted considerable attention due to its extensive existence in nature. In this study, we theoretically explored the spontaneous imbibition dynamics in a damaged V-shaped tree-like branching network by comparing with a parallel net with fixed constraints. Additionally, the imbibition capacity is characterized by two dimensionless quantities: imbibition potential and dimensionless imbibition time. The fractal theory is then used to generate the analytical expressions of these two dimensionless quantities. After that, the influence of structural parameters on the imbibition process is systematically investigated. It is found that a larger number of damaged channels will correspond to the lower imbibition potential and dimensionless imbibition time. Notably, the branching number N has an evident enhancement effect on the imbibition potential. A parameter plane is introduced to visualize parameter combinations, enabling the direct evaluation of the imbibition process in a specific network system. The physical mechanisms revealed by the proposed model provide effective guidance for imbibition process analysis in the damaged tree-like networks.

Bromelain crude extract to improve the emergence and growth of pepper seedlings

Pepper (Capsicum annuum L.) is one of the most consumed horticultural products worldwide. However, pepper seeds have slow and asynchronous germination. Organic agriculture encourages using natural substances for the pre-germinative treatment of seeds. The objective of the present work was to evaluate the effect of priming sweet pepper seeds with bromelain crude extract (obtained from pineapple stem residues) on subsequent seedling emergence and growth. The effects of the proteolytic activity of the extract (0, 3.16, 6.25, 12.25, and 25.0 totalU), imbibition time (0, 3, 6, 9, 12, and 15 h), and imbibition temperature (15, 25, 35 and 45 ℃) on seedling emergence and growth were assessed. The significantly best emergence, based on a range of indicators (emergence percentage: E, time to 50% emergence: TE50, emergence index: EI, mean emergence rate: MER, mean emergence time: MET, and synchronization index: SI), was obtained when the seeds were treated for three h at 35°C with a 6.25 totalU bromelain crude extract. Seeds subjected to this treatment combination also yielded the most vigorous seedlings (number of true leaves, length and thickness of the stems, fresh mass, dry mass, leaf area) . In conclusion, pre-germinative treatment with bromelain crude extract of 6.25 totalU proteolytic activity for three h at 35°C improved seedling emergence and growth in sweet pepper seedlings relative to untreated seed. This result offers an organic priming alternative for seeds of sweet pepper.

Simulation of water self-imbibition in nanometer throat-pore structure filled with oil

Water self-imbibition potentially serves as a driving force for shale oil recovery due to the sizeable capillary pressure in the nanometer pores of shale. Understanding the water self-imbibition mechanism at the nanometer pore-scale helps promote shale oil recovery. In this work, we performed the direct numerical simulation using the phase-field model to study water self-imbibition dynamics in the nanometer throat-pore structure filled with oil. The effects of throat/pore morphologies (throat size, coordination number, and pore shape) and fluid properties (interfacial tension, contact angle, and viscosity) on the water imbibition dynamics were studied in detail. We distinguished two types of imbibition processes and found that the throat/pore morphologies significantly affect the final oil displacement ratio. Meanwhile, the interfacial tension and water contact angle mainly influence the imbibition rate (i.e., the oil displacement rate), while the water viscosity influences both the imbibition rate and the final oil displacement ratio. A qualitative correlation of the imbibition time and fluid properties is deduced by comparing classical theory predictions and simulation results. The quantitative deviations caused by local confinement are delineated as well.

Optimization for ultrafast capillary-driven flow in open rectangular microchannels

The Lucas−Washburn (LW) equation has been extensively used to predict the imbibition length of capillary-driven flow. Using the hydraulic diameter for non-circular cross section in the LW equation is widely accepted. Accordingly, the larger the hydraulic diameter, the higher the imbibition rate. However, the validity of the LW equation for the optimization of capillary-driven flow in open rectangular microchannels remains an open question. In this study, we propose a theoretical model to predict the imbibition rate of capillary-driven flow in open rectangular microchannels. To validate the model, we conducted a series of experiments on spontaneous capillary-driven flow of water in open rectangular Si microchannels. We fabricated Si microchannels with hydraulic diameters ranging from 18 to 375 µm to investigate the dependence of the imbibition rate on the hydraulic diameter. The proposed model was consistent with the experimental results. In the case of microchannels with a fixed height, a plot of the measured imbibition rate against the hydraulic diameter was well fitted by a downward-opening parabolic curve, indicating that the imbibition rate had an optimal value at the aspect ratio (width to height) of two. For a given channel width, the imbibition rate increased with the hydraulic diameter, and it leveled off at a large hydraulic diameter for aspect ratios below 0.5. An ultrafast imbibition time of 1.97 s over an entire length of 70 mm was achieved, corresponding to the optimal imbibition rates of 40 mm/s at imbibition length x1 = 34 mm and 19 mm/s at x2 = 68 mm among the experimental cases.

Comparative changes in sugars and lipids show evidence of a critical node for regeneration in safflower seeds during aging.

During seed aging, there is a critical node (CN) where the population viability drops sharply. Exploring the specific locations of the CN in different species of plants is crucial for understanding the biological storage properties of seeds and refining seed life span management. Safflower, a bulk oil crop that relies on seeds for propagation, has a short seed life. However, at present, its biological characteristics during storage are not clear, especially the changes in metabolic capability and cell structures. Such knowledge is needed to improve the management of safflower seed life span and effective preservation in gene banks. Here, the seed survival curve of oilseed safflower under the controlled deterioration conditions of 60% relative humidity and 50°C was detected. The seed population showed an inverted S shape for the fall in germination. In the first 12 days of aging, germination remained above 86%. Prior to the CN at approximately day 10 (C10), when viability was in the "plateau" interval, seed vigor reduced at the same imbibition time point. Further analysis of the changes in sugar concentration found that the sucrose content decreased slowly with aging and the content of raffinose and two monosaccharides decreased abruptly at C10. Differentially metabolized lipids, namely lysophospholipids [lyso-phosphatidylcholine (LPC) and lyso-phosphatidylethanolamines (LPE)] and PMeOH, increased at day 3 of aging (C3). Fatty acid content increased by C6, and the content of phospholipids [phosphatidylcholines (PC), phosphatidylethanolamines (PE), and phosphatidylinositols (PI) and glycolipids [digalactosyl diacylglycerol, monogalactosyl diacylglycerol, and sulphoquinovosyl diglycerides (SQDG)] decreased significantly from C10. In addition, the activities of raffinose hydrolase alpha-galactosidase and the glyoxylate key enzyme isocitrate lyase decreased with seed aging. Confocal microscopy and transmission electron microscopy revealed shrinkage of the seed plasma membrane at C10 and the later fragmentation. Seedling phenotypic indicators and 2,3,5-triphenyltetrazolium chloride activity assays also verified that there were significant changes in seeds quality at the CN. In summary, the time point C10 is a CN during seed population aging. Before the CN, sugar and lipid metabolism, especially fatty acid metabolism into sugar, can make up for the energy consumed by aging. After this point, the seeds were irreversibly damaged, and their viability was greatly and rapidly reduced as the cell structure became increasingly destroyed.

Theoretical Investigation of Nonlinear-Diffusion Countercurrent Imbibition for Porous Medium with Micro-/Nanopores

Countercurrent imbibition is an important oil recovery mechanism in tight reservoir development. For tight oil reservoirs with hydraulic fractures and natural fractures, the injected fluid imbibes into a tight matrix from the fracture surface while crude oil flows reversely into the fracture during the process of liquid injection and soaking. Based on the traditional imbibition model, this paper proposes a countercurrent imbibition extension model for porous medium with micro-/nanopores, considering the early superdiffusion phenomenon under low water saturation. The reliability of this proposed model is further verified through experimental imbibition data and compared with the classical imbibition model. This model can obtain the dynamic evolution process of the imbibition saturation profile and quantify the countercurrent imbibition distance (imbibition range). The sensitivity analysis is then conducted, including the imbibition time, core length, characteristic parameters of relative permeability, characteristic parameters of capillary pressure, oil viscosity, and permeability. The results demonstrate that the countercurrent imbibition process can be divided into three stages: the superdiffusion stage (faster than t0.5), transition stage, and subdiffusion stage (slower than t0.5). Two key parameters, the critical imbibition saturation and its corresponding critical imbibition time, can be obtained through this model, which are significant to establishing reasonable soaking time for achieving higher oil recovery. This research improves the understanding of the countercurrent imbibition process, which explores the efficient development of water injection for tight oil reservoirs with micro-/nanopores.

Experimental Study on Hydraulic Fracture Initiation and Propagation in Hydrated Shale

Shale reservoirs contain a certain amount of clay minerals, which can hydrate through imbibition when in contact with various water-based fluids during drilling and completion. Shale hydration can lead to structural changes in the shale such as the expansion of bedding planes and propagation of microfractures, consequently affecting the initiation and propagation of hydraulic fractures. However, the effect of shale hydration under confining pressure on hydraulic fracture propagation and stimulation effect is still unclear. To this end, a novel experimental method integrating shale hydration and hydraulic fracturing was proposed based on the laboratory triaxial hydraulic fracturing simulation system. This method enables a more realistic simulation of shale hydration and hydraulic fracturing process happening in downhole conditions. The experimental results show that under simulated reservoir conditions, water imbibition increases over time with the imbibition rate reaching its peak within 24 h. The breakdown pressure, number of fractures, and complexity of fractures are positively correlated with imbibition time. The increase in fracture complexity could be attributed to the increase in the number of fractures. In contrast, imbibition pressure (injection pressure for imbibition) has little influence on water imbibition. For specimens under different imbibition pressure, the breakdown pressure and the number of fractures are close, and the complexity of fractures does not change prominently; all are T-shaped fractures. It is believed that the closure of microfractures under confining pressure caused by hydration is the main reason for the increase in breakdown pressure. Higher breakdown pressure means higher net pressure in the wellbore, which facilitates fracture initiation where the breakdown pressure is higher. Therefore, shale hydration is conducive to the initiation of multiple fractures, thus increasing the number and complexity of fractures.

Priming in lettuce seeds

One of the methods used to promote the rapid and uniform germination of vegetable seeds is the use of osmotic conditioning. The technique aims to regulate the osmotic potential of the solution, thus restricting the entry of water into the seeds without them germinating during the process. This work evaluated the germination of lettuce seeds of Grand Rapids, Everglades, and Verônica cultivars, submitted to osmotic conditioning. The seeds were immersed in polyethylene glycol solutions (PEG 6000) at potentials of 0.0; -0.6; -0.8, and -1.0 MPa, and remained in imbibition for 14, 24, and 48 h. After this period, the seeds were germinated on paper, moistened with water at 2.5 times their mass, and kept at 20ºC for seven days. The experimental design used was completely randomized, in a factorial scheme with three cultivars, four osmotic potentials, and three temperatures, with four replications of 25 seeds each. The germination percentage, the germination speed index, the mean speed of germination, and the mean germination time were evaluated. Data were subjected to analysis of residual normality by the Shapiro-Wilk test and the homogeneity of variances using the Bartlett test and submitted to analysis of variance. Data from osmotic potential and time of imbibition were submitted to polynomial regression. The treatment means were compared at 5% probability. Seeds of ‘Grand Rapids’ and ‘Everglades’ showed positive effects after osmoconditiong treatments.

Priming Strategies for Parsley Seedling Production

Parsley seeds are known for nonuniform and long germination; consequently, vegetable nurseries commonly use priming techniques to improve the production of parsley seedlings. The objectives of this study were 1) to characterize the imbibition curve of parsley seeds, 2) to evaluate the effect of different priming agents on parsley seedling production, and ultimately 3) to compare priming techniques for emergence and vigor of parsley’s seedlings, thus providing an optimal priming strategy for parsley seedling production. Using three priming agents—water (seeds imbibed for 24, 48, 72, and 96 hours), polyethylene glycol 6000 (PEG6000) (seeds imbibed at –0.5, –1.0, –1.5, and –2.0 MPa for 29, 58, 87, and 116 hours), and gibberellic acid (GA) (seeds imbibed at 0.5, 1.0, 1.5, and 2.0 g·L−1 a.i. of solution for 15, 30, 45, and 60 minutes), and two parsley cultivars (Krausa and Titan), three experiments evaluated parsley seedling parameters, including emergence speed index (ESI) and total emergence (TE) in a complete randomized block design (n = 4) each. In Expt. 1 (hydropriming), increasing water imbibition time (IT) reduced ESI on both parsley cultivars. In addition, the TE quadratically reduced with the increase of water IT. In Expt. 2 (osmopriming), there was no significant main effect or interaction of treatments on ESI. Regardless of PEG6000 concentration, the TE had a linear increase with the increase of IT for cultivar Krausa but not for cultivar Titan. In Expt. 3 (hormonal priming), there was a significant increase in ESI and TE with the increase in GA rate. Ultimately, strategies for analysis of best priming were water at 24 hours of IT, PEG6000 at –2.0 MPa for 116 hours of IT, and GA at 2.0 g·L−1 a.i. of solution for 15 minutes of IT. Once compared with an untreated seeds treatment, priming strategies of water imbibition for 24 hours and PEG6000 at –2.0 MPa for 116 hours had the highest ESI and TE.

Prediction of spontaneous imbibition in porous media using deep and ensemble learning techniques

Spontaneous imbibition (SI), which is a process of displacing a nonwetting fluid by a wetting fluid in porous media, is of critical importance to hydrocarbon recovery from fractured reservoirs. In the present study, we utilize deep and ensemble learning techniques to predict SI recovery in porous media under different boundary conditions including All-Faces-Open (AFO), One-End-Open (OEO), Two-Ends-Open (TEO), and Two-Ends-Closed (TEC). An extensive experimental dataset reported in literature representing a multiplicity of non-wetting fluid recovery-time curves was used in our analysis. The prepared dataset was used to learn diverse ensemble and deep learning algorithms of Random Forest (RF), Gradient Boosting Machine (GBM), Extreme Gradient Boosting (XGBoost), Light Gradient Boosting Machine (LightGBM), Voting Regressor (VR), Convolutional Neural Network (CNN), Long Short-Term Memory (LSTM), and Gated Recurrent Unit (GRU). The training procedure provided us with robust models linking the SI recovery to the absolute permeability (k), porosity (ϕ), characteristic length (Lc), interfacial tension (σ), wetting-phase viscosity (μw), non-wetting-phase viscosity (μnw), and imbibition time (t). To evaluate and validate the models’ prediction, we used two well-established approaches: (i) 10-fold cross-validation and (ii) predicting the SI behavior of a set of unseen data excluded from the model training. Our results illustrate an excellent performance of deep and ensemble learning techniques for prediction of SI with the test RMSE values of 4.642, 4.088, 4.524, 3.933, 3.875, 3.975, 4.513, and 4.807 percent for RF, GBM, XGBoost, LightGBM, VR, CNN, LSTM, and GRU models, respectively. The models have significant benefits in terms of accuracy and generality. Furthermore, they alleviate the sophistications associated with tuning the traditional correlation functions. The findings of this study can pave the road toward a more comprehensive characterization of fluid flow in porous materials which is important to a wide range of environmental and energy-related challenges such as contaminant transport, soil remediation, and enhanced oil recovery.

Time-dependent shape factor for scaling of multi-dimensional counter-current imbibition with different boundary conditions

The scaling laws are critically important in researching the characteristics of spontaneous imbibition and predicting oil and gas recovery from fractured reservoirs. This paper focuses on developing a shape factor for scaling the multi-dimensional counter-current imbibition processes. We studied the multi-dimensional imbibition characteristics by establishing numerical simulation models considering nine boundary conditions. On the basis of the capillary diffusion equation of counter-current imbibition, the equations of normalized oil recovery versus imbibition time were obtained under different boundary conditions. Then, we derived a new shape factor by processing and comparing these equations. The results show that the relationship between front distance and imbibition time of 2D and 3D models is different from that of 1D models. The shape factor for the multi-dimensional counter-current imbibition processes is time-dependent and varies with normalized recovery, which is also the reason for the difficulty of using a constant shape factor to scale imbibition data. Numerical simulation results and experimental data validated that the scaling equation could correlate the effect of differences in boundary conditions by introducing the new shape factor.

Differences in Imbibition Efficiency Between Bedding and Tectonic Fractures in the Lucaogou Formation in the Jimusar Sag: Evidence From Simulation Experiments

In addition to tectonic fractures, the ubiquitous and important bedding fractures are often overlooked in the imbibition processes. Based on the identification of different fracture types in tight sandstone from the middle Permian Lucaogou Formation in the Jimusar Sag, NW China, spontaneous imbibition of water experiments was carried out, aiming to investigate the effect of tectonic and bedding fractures on hydrocarbon recovery efficiency in tight reservoir rocks. The results show that the difference in connectivity between the vertical (tectonic fractures) and horizontal (bedding fractures) directions of pores and pore throats is the main reason for the distinction in microscale permeability and, hence, fluid imbibition. The difference in the time required for imbibition between bedding and tectonic fractures is subtle, but the former is slightly lower than the latter in terms of imbibition depth and efficiency. Higher temperatures can shorten the reaction time of imbibition. On the basis that the tectonic fractures are opened, opening the same scale of bedding can increase the imbibition effectiveness by 8.7% at reservoir conditions (27 MPa, 80°C), and the closer to the fracture, the higher the imbibition efficiency in the matrix. The samples with higher porosity and permeability per unit volume have high imbibition oil recovery. However, the imbibition efficiency of the samples with lower porosity and permeability is higher, i.e., the final imbibition efficiency is inversely proportional to porosity and permeability.

A Comparison of Water Imbibition and Controlled Deterioration in Five Orthodox Species

Orthodox seeds deteriorate even when stored in the best of conditions; hence, it is very important to monitor germination in stored seeds. To assess orthodox seed deterioration, a germination test is usually employed. This study assessed and compared seed deterioration in five orthodox species using electrolyte leakage and Fourier transform infrared spectroscopy (FTIR). The study also compared water imbibition by the test orthodox seeds. To achieve this, the seeds from three wild (Bolusanthus speciosus; Combretum erythrophyllum; Erythrina caffra) and two agricultural (Pisum sativum and Cucurbita pepo) species were imbibed between 20 layers of single-ply paper towel. The other set was subjected to controlled deterioration at 40 °C and 100% relative humidity for 32 d, with samples taken for germination and electrolyte leakage measurement at 4 d intervals. FTIR measurements were performed at 0, 20, and 32 d of controlled deterioration. The results indicated that there were some significant interspecies differences in the imbibition times and seed water contents but these were not large. In all species, uptake of water was complete between about 15 and 25 h. The wild species showed higher sensitivity to controlled deterioration. Complete loss of germinability occurred much earlier in the wild species (20 d in B. speciosus and E. caffra, and 16 d in Co. erythrophyllum) compared with 36 d for the agricultural species P. sativum and Cu. pepo. There was a negative correlation between electrolyte leakage and seed germination in all wild and agricultural species. A strong positive correlation was observed between the time of controlled deterioration, electrolyte leakage, and FTIR transmission in all the species. While controlled deterioration may help in decisions relating to the storage of orthodox seeds, the water imbibition results from this study will help to set the priming time of the species. The study reaffirms electrolyte leakage as an indicator of seed viability in P. sativum and Cu. pepo; it also recommends the use of electrolyte leakage as an indicator of seed deterioration in B. speciosus, Co. erythrophyllum, and E. caffra. The study also recommends FTIR as a tool for monitoring the germination of stored seeds of all the test species.

Mucilage affects seed water imbibition and germination time of subtropical monsoonal forbs

The role of seed mucilage in the moist environments of monsoonal subtropics is poorly understood. We studied germination of six forb species from subtropical monsoonal China. Mucilage presence had little to no effect on germination percentage (G%), except for a significant decline for the large-seeded Prunella vulgaris. Dark treatments reduced G% for all species, while the combination of mucilage removal and high temperatures delayed the mean germination time (MGT). Seed fresh mass was negatively correlated with G%, but only for intact seeds incubated at 12/12 hours of 25/35 °C. The MGT of de-mucilaged seeds varied with seed shape index, also under the warmer temperature regime. Temperature and light are fundamental to drive germination processes, and the presence of mucilage influences MGT of subtropical monsoonal species. Presence or absence of mucilage had little to no difference in germination percentage, but can be important to drive germination timing, also promoting water uptake and seed adhesion to soil.

Experimental Study of Influence of Core Wettability on Imbibition Properties

Through new core wettability simulation technology and the single-sided unidirectional imbibition experimental method, the influence of core wettability on oil imbibition characteristics was studied by using artificial cores with wettability index in the range of −0.9~0.95. Results show that for the cores with permeability from ultra-low to medium–high, the imbibition time shows a monotonically decreasing law with the increase in the wettability index. In the weak water-wet range, the imbibition time increases significantly with the weakening of water-wet. Oil imbibition rate goes up with the increase in wettability index. In the strong water-wet range, the imbibition rate will change significantly with wettability. In the water-wet zone, there is a positive correlation between imbibition oil limit recovery and wettability index, according to which a power exponent model of them is established. The imbibition–displacement ratio, which characterizes the contribution rate of oil recovery by imbibition to that by waterflooding, is also positively correlated with the wettability index. In addition, imbibition–displacement ratios of extra-low permeability cores are very close to that of medium–high permeability cores. According to the analysis of the research results, compared with the strongly water-wet oil layer, the weakly water-wet oil layer with a wettability index of 0–0.5 has a greater contribution to oil recovery by using the enhanced imbibition method.

Sprouts Use as Functional Foods. Optimization of Germination of Wheat (Triticum aestivum L.), Alfalfa (Medicago sativa L.), and Radish (Raphanus sativus L.) Seeds Based on Their Nutritional Content Evolution

Wheat, alfalfa, and radish sprouts are well-renowned for their high nutritional content. However, their optimal imbibition and germination durations are rarely considered in the literature. In this study, reduced imbibition times of 3 h, 10 h, and 4 h were demonstrated for the wheat, alfalfa, and radish seeds, respectively. The evolution of their crude fat, proteins, polyphenols, antioxidant activity, and vitamins were investigated over 7 days of germination. The crude fat and protein loads of these sprouts slightly varied during germination, whereas the phenolic compounds and antioxidant activity maxed out at day 7, 5, and 6 for the wheat, alfalfa, and radish sprouts, respectively, with significant levels of catechin. The vitamins highly increased, showing noteworthy yet different peaks of growth depending on the seed and the vitamin analyzed. Interestingly, alfalfa and radish sprouts, taken at their optimal germination day, would decidedly contribute to meet our Recommended Daily Allowances (RDAs) of vitamins E, A, and B6. Overall, for a greater nutritional content and a potential use of these sprouts as nutraceutical ingredients, our results suggested to leave the wheat, alfalfa, and radish seeds to germinate only over 7, 4, and 6 days, respectively, after which their nutritional quality tended to decrease.

Characteristic Forced and Spontaneous Imbibition Behavior in Strongly Water-Wet Sandstones Based on Experiments and Simulation

Forced and spontaneous imbibition of water is performed to displace oil from strongly water-wet Gray Berea (~130 mD) and Bentheimer (~1900 mD) sandstone core plugs. Two nonpolar oils (n-heptane and Marcol-82) were used as a non-wetting phase, with viscosities between 0.4 and 32 cP and brine (1 M NaCl) for the wetting phase with viscosity 1.1 cP. Recovery was measured for both imbibition modes, and pressure drop was measured during forced imbibition. Five forced imbibition tests were performed using low or high injection rates, using low or high oil viscosity. Seventeen spontaneous imbibition experiments were performed at four different oil viscosities. By varying the oil viscosity, the injection rate and imbibition modes, capillary and advective forces were allowed to dominate, giving trends that could be captured with modeling. Full numerical simulations matched the experimental observations consistently. The findings of this study provide better understanding of pressure and recovery behavior in strongly water-wet systems. A strong positive capillary pressure and a favorable mobility ratio resulting from low water relative permeability were main features explaining the observations. Complete oil recovery was achieved at water breakthrough during forced imbibition for low and high oil viscosity and the recovery curves were identical when plotted against the injected volume. Analytical solutions for forced imbibition indicate that the pressure drop changes linearly with time when capillary pressure is negligible. Positive capillary forces assist water imbibition, reducing the pressure drop needed to inject water, but yielding a jump in pressure drop when the front reaches the outlet. At a high injection rate, capillary forces are repressed and the linear trend between the end points was clearer than at a low rate for the experimental data. Increasing the oil viscosity by a factor of 80 only increased the spontaneous imbibition time scale by five, consistent with low water mobility constraining the imbibition rate. The time scale was predicted to be more sensitive to changes in water viscosity. At a higher oil-to-water mobility ratio, a higher part of the total recovery follows the square root of time. Our findings indicate that piston-like displacement of oil by water is a reasonable approximation for forced and spontaneous imbibition, unless the oil has a much higher viscosity than the water.