Capillary Desaturation Curves Research Articles

Entrapment and mobilization dynamics during the flow of viscoelastic fluids in natural porous media: A micro-scale experimental investigation

Capillary desaturation process was investigated as a function of wetting phase rheological signatures during the injection of Newtonian and non-Newtonian fluids. Two sets of two-phase imbibition flow experiments were conducted on a water-wet sandstone core sample using brine and viscoelastic polymer solutions. During the experiments, a high-resolution micro-computed tomography scanner was employed to directly map pore-level fluid occupancies within the pore space. The results of the experiments revealed that at a given capillary number, the viscoelastic polymer was more efficient than the brine in recovering the non-wetting oil phase. At low capillary numbers, this is attributed to the improved accessibility of the viscoelastic polymer solution to the entrance of pore elements, which suppressed snap-off events and allowed more piston-like and cooperative pore-body filling events to contribute to oil displacement. For intermediate capillary numbers, the onset of elastic turbulence caused substantial desaturation, while at high capillary numbers, the superimposed effects of higher viscous and elastic forces further improved the mobilization of the trapped oil ganglia by the viscoelastic polymer. In the waterflood, however, the mobilization of oil globules was the governing recovery mechanism, and the desaturation process commenced only when the capillary number reached a threshold value. These observations were corroborated with the pore-level fluid occupancy maps produced for the brine and viscoelastic polymer solutions during the experiments. Furthermore, at the intermediate and high capillary numbers, the force balance and pore-fluid occupancies suggested different flow regimes for the non-Newtonian viscoelastic polymer. These regions are categorized in this study as elastic-capillary- and viscoelastic-dominated flow regimes, different from viscous-capillary flow conditions that are dominant during the flow of Newtonian fluids. Moreover, we have identified novel previously unreported pore-scale displacement events that take place during the flow of viscoelastic fluids in a natural heterogeneous porous medium. These events, including coalescence, fragmentation, and re-entrapment of oil ganglia, occurred before the threshold of oil mobilization was reached under the elastic-capillary-dominated flow regime. In addition, we present evidence for lubrication effects at the pore level due to the elastic properties of the polymer solution. Furthermore, a comparison of capillary desaturation curves generated for the Newtonian brine and non-Newtonian viscoelastic polymer revealed that the desaturation process was more significant for the viscoelastic polymer than for the brine. Finally, the analysis of trapped oil clusters showed that the ganglion size distribution depends on both the capillary number and the rheological properties of fluids.

A Comprehensive Review on the Capillary Desaturation Curves for Sandstone and Carbonate Reservoirs

Summary Various enhanced oil recovery (EOR) methods are applied after primary and secondary recovery stages to target remaining oil saturation (ROS). This remaining oil is divided into bypassed oil and capillary-trapped residual oil. Mobilizing the residual oil in the reservoir is usually achieved when viscous or gravity forces exceed capillary forces. The recovery of the microscopically trapped residual oil is mainly studied using capillary desaturation curve (CDC). To optimize the design of various EOR methods in carbonate and sandstone reservoirs, a fundamental understanding of CDC is needed. A thorough and well-documented research study has been performed for determining the residual oil and generating CDC in sandstone rocks. However, a very limited amount of work has been reported on carbonate rocks. Thus, the main objective of this paper is to provide the recent development made over the last few decades on the CDC studies for carbonate and sandstone reservoirs. Different CDC studies were discussed based on the trapping/bond/capillary number and were critically analyzed. Furthermore, the effects of different controlling factors—wettability, permeability, interfacial tension (IFT), and heterogeneity—on CDC were investigated. This review analysis indicates that CDC in carbonate rocks is broader as opposed to sandstone rocks. This is because of the presence of micropores, large pore size distribution, complex geological characteristics, chemical reactivity, mixed-to-oil-wet characteristics, and heterogeneity of carbonate rocks. Moreover, the critical capillary number for water injection in carbonate rocks reported in the literature lies between 10–8 and 10–5. On the other hand, for sandstone rocks, the number ranges between 10–5 and 10–2. Furthermore, a major influence of wettability on the shape of the CDC was observed. The CDC shape is broader for oil-wet rocks, and capillary number values are higher compared to water-wet and mixed-wet rocks. On the other hand, the lowest capillary number values are observed in water-wet rocks. The outcome of this research study will provide a way forward for CDC studies in both sandstone and carbonate rocks. Additionally, it will serve as a baseline for understanding various CDCs and hence better screening of various EOR methods for different types of reservoir rocks.

Effects of trapping number on biopolymer flooding recovery of carbonate reservoirs

The effects of trapping number on enhanced oil recovery by schizophyllan biopolymer flooding in carbonate reservoirs were investigated by running several 1D simulations using measured reservoir rock and fluid data. Sensitivity analysis was performed on different uncertain parameters to history match the oil recovery obtained in the core flooding experiment. These parameters include inaccessible pore volume (IPV), biopolymer adsorption, permeability reduction factor, shear rate coefficient, hardness of injection water, and trapping number. The IPV, biopolymer adsorption, permeability reduction factor, shear rate coefficient and hardness of injection water have negligible effects on oil recovery by biopolymer flooding. Also, history matching of oil recovery data was not possible when these parameters were varied within their typical range of values. When trapping number effect was considered through capillary desaturation curve (CDC), residual oil saturation was reduced from 25.1% without considering its effect or under low trapping number to 10.0%, and the fitting effect for recovery was better. Therefore, we can't neglect the trapping number effect during biopolymer flooding simulation in the carbonate reservoirs.

A Brief Review of Capillary Number and its Use in Capillary Desaturation Curves

Capillary number, understood as the ratio of viscous force to capillary force, is one of the most important parameters in enhanced oil recovery (EOR). It continues to attract the interest of scientists and engineers, because the nature and quantification of macroscopic capillary forces remain controversial. At least 41 different capillary numbers have been collected here from the literature. The ratio of viscous and capillary force enters crucially into capillary desaturation experiments. Although the ratio is length scale dependent, not all definitions of capillary number depend on length scale, indicating potential inconsistencies between various applications and publications. Recently, new numbers have appeared and the subject continues to be actively discussed. Therefore, a short review seems appropriate and pertinent.

Capillary Desaturation Curves For Evaluating Surfactant Performance By Core Flooding Experiments

Capillary desaturation curves are normally generated in laboratory scale by means of core flooding experiments to evaluate the surfactant formulations for chemical injection in EOR projects. Low tension surfactant solution is the only liquid that could increase the dimensionless capillary number in order of magnitude of 103. Two types of core samples have been used in core flooding experiments to develop capillary desaturation curves, i.e., generic and standard Classhach core samples. In Addition, VS surfactant and additional alcohols are also used in these experiments. The higher the capillary number could generate a lower the residual oil saturation. Moreover, each rock may have a particular capillary desaturation curve depending on the rock properties. Therefore before implementing chemical injection in a pilot scale, capillary desaturation curve should be developed in laboratory to evaluate the surfactant injection performance.

Dissolution and remobilization of NAPL in surfactant-enhanced aquifer remediation from microscopic scale simulations

In this paper, the dissolution and mobilization of non-aqueous phase liquid (NAPL) blobs in the Surfactant-Enhanced Aquifer Remediation (SEAR) process were upscaled using dynamic pore network modeling (PNM) of three-dimensional and unstructured networks. We considered corner flow and micro-flow mechanisms including snap-off and piston-like movement for two-phase flow. Moreover, NAPL entrapment and remobilization were evaluated using force analysis to develop the capillary desaturation curve (CDC) and predict the onset of remobilization. The corner diffusion mechanism was also applied in the modeling of interphase mass transfer to represent NAPL dissolution as the dominant mass transfer process. In addition, the effect of pore-scale heterogeneity on mass transfer rate coefficient and recovered residual NAPL was considered in the simulations. Sodium dodecyl sulfate (SDS) and Triton X-100 were used as the surfactant for the SEAR process. The results indicate that although surfactants enhance NAPL recovery during two-phase flow, surfactant-enhanced remediation of residual NAPL through dissolution is highly dependent on surfactant type. When SDS ─as a surfactant with high critical micelle concentration (CMC) and low micelle partition coefficient (Km)─ was injected into a NAPL contaminated site, the mass transfer rate coefficient decreased (due to considerable changes in interface chemical potentials) which leads to a significant reduction in NAPL recovery after the end of two-phase flow. In contrast, Triton X-100 (with low CMC and high Km) improved NAPL recovery, by enhancing solubility at surfactant concentrations greater than CMC which overcompensates the interphase mass transfer reduction.

Capillary Desaturation Tendency of Hybrid Engineered Water-Based Chemical Enhanced Oil Recovery Methods

Several studies have shown the synergetic benefits of combining various chemical enhanced oil recovery (CEOR) methods with engineered waterflooding (EWF) in both sandstones and carbonate formations. This paper compares the capillary desaturation tendency of various hybrid combinations of engineered water (EW) and CEOR methods with their conventional counterparts. Several coreflood experiments were conducted, including EW-surfactant flooding (EWSF), EW-polymer flooding (EWPF), EW-alkali-surfactant flooding (EWASF), EW-surfactant-polymer flooding (EWSPF), and EW-alkali-surfactant-polymer flooding (EWASP). Capillary numbers (Nc) and corresponding residual oil saturation (Sor) for each scenario are compared with capillary desaturation curves (CDC) of conventional CEOR methods from the literature. The results indicate that hybrid EW–CEOR methods have higher capillary desaturation tendency compared to conventional methods. The capillary numbers obtained by standalone polymer flooding (PF) are usually in the range from 10−6 to 10−5, which are not sufficient to cause a significant reduction in Sor. However, the hybrid EW-polymer flooding approach considerably reduced the Sor for the same Nc values, proving the effectiveness of the investigated method. The hybrid EWASP flooding caused the highest reduction in Sor (23%) against Nc values of 8 × 10−2, while conventional ASP flooding reduced the Sor for relatively higher Nc values (3 × 10−3 to 8 × 10−1). Overall, the hybrid methods are 30–70% more efficient in terms of recovering residual oil, compared to standalone EWF and CEOR methods. This can be attributed to the combination of different mechanisms such as wettability modification by EW, ultralow interfacial tension by alkali and surfactant, reduced surfactant adsorption by alkali addition, and favorable mobility ratio by polymer. Based on the promising results, these hybrid techniques can be effectively implemented to carbonate formations with harsh reservoir conditions such as high salinity and high temperature.

Experimental studies of the capillary desaturation curve in polymer-surfactant flooding

The paper presents the results of laboratory studies of polymer-surfactant flooding on core samples of different permeability. The obtained data are used in hydrodynamic modeling.
 Experimental studies included:
 • study of the dynamics of oil displacement, plotting the dependence of the residual oil saturation on the surfactant concentration – interfacial tension at the interface of the surfactant-oil solution;
 • comparative experimental studies of residual oil saturation when oil is displaced by surfactant compositions of various manufacturers;
 • comparative studies of phase permeability in flood experiments for the filtration of oil and water, oil and polymer-surfactant solution at different ratios in the flow.

Capillary desaturation curve: does low salinity surfactant flooding significantly reduce the residual oil saturation?

Different oil displacement experiments conducted on sandstone and carbonate samples show that low salinity water (LSW) injection can reduce the residual oil saturation (ROS). Recently, surfactant flooding (SF) in combination with low salinity water (known as low salinity surfactant (LSS) flooding) is proposed as a potentially promising hybrid enhanced oil recovery (EOR) process. A lower ROS is reported for a LSS process compared to that seen in SF or with LSW at the same capillary number. The capillary desaturation curve (CDC) is a well-known tool to study the effect of viscous and capillary forces on ROS for different EOR techniques. In this study, ROS data of various LSW, SF, and LSS flooding experiments at different capillary numbers are collected to develop a CDC to analyze the performance of the hybrid LSS method. This can help to analyze the effect of the hybrid method on an extra improvement in sweep efficiency and reduction in residual oil. A lower ROS is observed for LSS compared to LSW and SF in the same capillary number range. Our study shows different behaviors of the hybrid method at different ranges of capillary numbers. Three regions are identified based on the capillary number values. The difference in ROS is not significant in the first region (capillary number in the range of 10−7–10−5), which is not applicable in the presence of surfactant due to the low interfacial tension value. A significant reduction in ROS is observed in the second region (capillary number in the range of 10−5–10−2) for LSS compared to SF. This region is the most practical range for SF and LSS flooding. Hence, the application of LSS provides a noticeable benefit compared to normal EOR techniques. In the third region (capillary numbers greater than 10−2), where the surfactant flooding is a better performer, the difference in ROS is negligible.

Uncertainty quantification of shale capillary desaturation curves for surfactant EOR in shale through fracturing fluids using predictive modeling

Surfactant is often added into hydraulic fracturing fluids for shale reservoirs because it can minimize formation damage. The surfactant is also known for its EOR potential for sandstone/ carbonate reservoirs. Given both benefits, some previous papers studied the feasibility of surfactant EOR for shale reservoirs. Evaluation of surfactant EOR potentials requires accurate capillary desaturation curves (CDCs) of the shale rocks because CDCs determine how easily the surfactant will recover the residual oil saturation and improve the relative permeabilities.However, there is currently no experimental CDC data of shale rocks because of the difficulty in the experiment. This study builds a validated predictive model to quantify the effect of the CDC uncertainty on EOR. The objective is to numerically assess how the CDCs uncertainty affects the feasibility of surfactant EOR in shale reservoirs using Monte Carlo simulation of 100,000 possible CDCs. This paper also performs sensitivity analysis on the surfactant’s wettability alteration direction and its alteration extent and target interfacial tension value. Our model reveals that surfactants can offer optimum EOR potentials in shale reservoirs if they strongly alter the shale’s wettability to water-wet while maintaining a high interfacial tension. However, even when using such optimum surfactants, there are still some possibilities of decreasing the ultimate oil recovery because of the CDC uncertainty. Lastly, this study quantitatively presents the degree of the risks.

Computational Fluid Dynamics to develop novel correlations for residual saturation of the displaced fluid in a capillary tube

The main goal of this study is to numerically investigate the immiscible fluid-fluid displacement at the micro-level under low inertial and buoyancy forces. To this end, a micro capillary tube was constructed, and the fluid-fluid interface and fluid-fluid-wall triple line were tracked using VOF (Volume of Fluid)-CSF (Continuum Surface Force) strategy. Mesh-independency analysis was conducted by utilizing the Adaptive Mesh-Refinement (AMR) technique. Simulation results agreed well with the experimental data obtained from literature with the AARD (Average Absolute Relative Deviation) of around 10%. The validated model was then used to generate the CDC (Capillary Desaturation Curve) curves for different wall wettabilities, considering the dynamic contact angle in the simulations. The generated CDC curves at the breakthrough time showed that there are three different zones, namely low-Ca, transitional, and high-Ca region. The only difference between saturation profiles of different wettabilities was in the transition zone, based on the CDC analysis. The saturation and velocity profiles at the central plane of the tube were constructed and compared. Phase separation can happen depending on Ca number and the magnitude of the dynamic contact angle. Eventually, outcomes of the numerical simulator were used to develop new correlations for the residual saturation as functions of dynamic contact angle and Ca number. Nonlinear regression analysis with Levenberg-Marquart algorithm was used to find coefficients of the correlations. The developed correlations showed to be highly robust for the transition and high-Ca regions with the correlation coefficients (R2) up to 0.96 and the maximum AARD of 12%. Results of this study are applicable to both capillary-fingering and viscous-fingering flow-regimes based on the Lenormand's phase-diagrams.

Experimentally based pore network modeling of NAPL dissolution process in heterogeneous porous media

Practical designs of non-aqueous phase liquids (NAPLs) remediation strategies require reliable modeling of interphase mass transfer to predict the retraction of NAPL during processes such as dissolution. In this work, the dissolution process of NAPL during two-phase flow in heterogeneous porous media is studied using pore-network modeling and micromodel experiments. A new physical-experimental approach is proposed to enhance the prediction of the dissolution process during modeling of interphase mass transfer. In this regard, the normalized average resident solute concentration is evaluated for describing the dissolution process at pore-level. To incorporate the effect of medium heterogeneities, a new experimental factor is considered for enhancing corner diffusion modeling. In addition, capillary desaturation curves (CDCs) are predicted during hydraulic flow modeling to estimate initial residual NAPL saturation. The developed network model can predict residual NAPL saturations and mass transfer rate coefficient for a NAPL-water system at different injection rates and fluid saturations. The evaluated mass transfer rate coefficients using the proposed physical-experimental approach show a significant improvement compared to either mechanistic or empirical methods. The proposed approach in this study can be attractive for possible applications in commercial simulators of contaminant transport in porous media.

Impact of injection rate on transient oil recovery under mixed-wet conditions: a microfluidic study

Lab-on-a-chip methods were used to visualize the pore-scale distribution of oil within a mixed-wet, quasi-monolayer of marble grains packed in a microfluidic channel as the oil was displaced by water. Water injection rates corresponding to microscopic capillary numbers between Ca = 5 × 10-8 and 2 × 10-4 (Darcy velocities between 0.3 and 1100 ft/d) were considered. As expected, early-time water invasion transitions from stable displacement to capillary fingering with decreasing Ca, with capillary fingering observed at Ca ≤ 10-5. End-point oil saturation decreases with Ca over the entire range of Ca considered, consistent with the canonical capillary desaturation curve. In contrast, Sor derived from approximate numerical simulations using reasonable Pc(Sw) do not display a strong dependence on Ca. These results suggest that the Ca dependence of end-point oil saturation is largely due to capillary end effects which, under conditions considered presently, affect the entire length of the packed bed.

Coupled supercritical CO2 dissolution and water flow in pore-scale micromodels

Dissolution trapping is one of the most important mechanisms for geological carbon storage (GCS). Recent laboratory and field experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and coupled scCO2 dissolution and water flow, i.e., scCO2 dissolution at local pores/pore throats creating new water-flow paths, which in turn enhance dissolution by increased advection and interfacial area. However, the impacts of pore-scale characteristics on these coupled processes have not been investigated. In this study, imbibition and dissolution experiments were conducted under 40 °C and 9 MPa using a homogeneous/isotropic hexagonal micromodel, two homogeneous elliptical micromodels with low or high anisotropy, and a heterogeneous sandstone-analog micromodel. The four micromodels, initially saturated with deionized (DI)-water, were drained by injecting scCO2 to establish a stable scCO2 saturation. DI water was then injected at different rates with logCa (the capillary number) ranging from −6.56 to −4.34. Results show that bypass of scCO2 by displacing water is the dominant mechanism contributing to the residual CO2 trapping, triggered by heterogeneity in pore characteristics or pore-scale scCO2-water distribution. Bypass can be enhanced by pore heterogeneity or reduced by increasing transverse permeability, resulting in relatively low (<2% of CO2 solubility) or high (9–13% of CO2 solubility) dissolved CO2 concentration in displacing water. The overall dissolution of residual scCO2 increases with decreasing Ca, and approaches to their solubility at low Ca value with sufficient residence time. This main trend is similar to a capillary desaturation curve that represents the relationship between the residual saturation and Ca. Spatially, dissolution initiates along the boundary of bypassed scCO2 cluster(s) in a non-equilibrium manner, and the coupling of water flow and dissolution occurs which fragments the bypassed scCO2 clusters and enhance scCO2 dissolution.

Capillary Desaturation Curve for Residual Nonwetting Phase in Natural Fractures

Summary The displacement of a nonwetting phase by a wetting phase is characterized by the capillary number. Different forms of capillary number have been used in the literature for flow in porous media. A capillary number for a single rock fracture has been defined in the literature, using the mean aperture to characterize the trapping and mobilization in a fracture. We propose a new capillary-number definition for fractures that incorporates geometrical characterization of the fracture, dependent on the force balance on a trapped ganglion. The new definition is validated with laboratory experiments using five distinctive model fractures. The model fractures are made of glass plates, with a wide variety of hydraulic apertures, degrees of roughness, and correlation lengths of the roughness. The fracture surfaces were characterized in detail and statistically analyzed. The aperture distribution of each model fracture was represented as a 2D network of pore bodies connected by throats. The hydraulic aperture of each model fracture was measured experimentally. Capillary desaturation curves (CDCs) were generated experimentally using water/air in forced imbibition. The transparent nature of the system permits us to determine the residual air saturation as a function of pressure gradient from the captured images. The residual nonwetting saturation/capillary-number relationship obtained from different fractures varying in aperture and roughness can be represented approximately by a single curve in terms of the new definition of the capillary number. They do not fit a single trend using the conventional definition of the capillary number.

Early gait abnormalities relate to brainstem and spinal cord pathology in CLN1 disease

Dissolution trapping is one of the most important mechanisms for geological carbon storage (GCS). Recent laboratory and field experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and coupled scCO2 dissolution and water flow, i.e., scCO2 dissolution at local pores/pore throats creating new water-flow paths, which in turn enhance dissolution by increased advection and interfacial area. However, the impacts of pore-scale characteristics on these coupled processes have not been investigated. In this study, imbibition and dissolution experiments were conducted under 40°C and 9 MPa using a homogeneous/isotropic hexagonal micromodel, two homogeneous elliptical micromodels with low or high anisotropy, and a heterogeneous sandstone-analog micromodel. The four micromodels, initially saturated with deionized (DI)-water, were drained by injecting scCO2 to establish a stable scCO2 saturation. DI water was then injected at different rates with logCa (the capillary number) ranging from −6.56 to −4.34. Results show that bypass of scCO2 by displacing water is the dominant mechanism contributing to the residual CO2 trapping, triggered by heterogeneity in pore characteristics or pore-scale scCO2-water distribution. Bypass can be enhanced by pore heterogeneity or reduced by increasing transverse permeability, resulting in relatively low (<2% of CO2 solubility) or high (9–13% of CO2 solubility) dissolved CO2 concentration in displacing water. The overall dissolution of residual scCO2 increases with decreasing Ca, and approaches to their solubility at low Ca value with sufficient residence time. This main trend is similar to a capillary desaturation curve that represents the relationship between the residual saturation and Ca. Spatially, dissolution initiates along the boundary of bypassed scCO2 cluster(s) in a non-equilibrium manner, and the coupling of water flow and dissolution occurs which fragments the bypassed scCO2 clusters and enhance scCO2 dissolution.

MRI study on CO2 capillary trap and drainage behavior in sandstone cores under geological storage temperature and pressure

Capillary pressure is an important parameter to characterize the core properties in CO2 geological storage applications, and it is necessary to study the CO2 drainage behavior to predict the potential and ensure the safety of storage. In this work, we conducted CO2 drainage experiments in two types of sandstone cores (Berea sandstone and synthetic sandstone) under reservoir conditions (800 m underground) and measured the capillary pressure using an MRI system. The drainage experiments were repeated in a capillary number range from 5.22 × 10−9 to 5.5 × 10−7 by varying the injection rate. The entry pressure and pore size distribution index were calculated by fitting a straight line on a log-log curve of the effective saturation versus capillary pressure. Relative permeability curves were plotted using the calculated entry pressure and pore size distribution index. The curves were consistent with the properties of the sandstone cores. The capillary desaturation curves gave the irreducible brine saturations for different permeability, wettability, injection pressure and injection direction conditions as a function of capillary number.

Impact of heterogeneous properties of soil and LNAPL on surfactant-enhanced capillary desaturation

This paper investigates low-concentration (<1wt%) surfactant flushing when used as a follow-up technology for multiphase vacuum extraction on heterogeneous sites. Challenges posed by soil permeability, pore-size distribution, mineralogy, light non-aqueous phase liquid (LNAPL) weathering and groundwater hardness were quantified through batch and soil column tests. Compatibility issues between the mixed mineralogy soils, hard groundwater, mixed LNAPL and usual anionic surfactants were observed. The selected solution was a Winsor type I system promoting an interfacial tension of 0.06mN/m between the site LNAPL and the amphoteric surfactant CAS in aqueous solution at pH12. Surfactant loses to adsorption and pore media plugging were observed in the fine soil fraction. The capillary desaturation curves (CDC) obtained with the column tests suggested mixed-wettability behavior. The soil permeability strongly influenced LNAPL recovery, as expressed by the relationship obtained between capillary numbers (NCa) and hydraulic gradients. In this case, the critical NCa, marking the onset of capillary desaturation, could only be obtained with realistic hydraulic gradients in the coarse soil fraction. At those gradients, potential LNAPL recovery was 30% at the most. Unlike previously published CDCs, the relationship between NCa (log-scale) and LNAPL recovery was not linear but dependant on residual LNAPL saturation.

New capillary number definition for displacement of residual nonwetting phase in natural fractures

AbstractWe propose a new capillary number for flow in fractures starting with a force balance on a trapped ganglion in a fracture. The new definition is validated with laboratory experiments using five distinctive model fractures. Capillary desaturation curves were generated experimentally using water‐air forced imbibition. The residual saturation‐capillary number relationship obtained from different fractures, which vary in aperture and roughness, can be represented approximately by a single curve in terms of the new definition of the capillary number. They do not fit a single trend using the conventional definition of the capillary number.

Consideration on Data Dispersion for Two-Phase Flow Micromodel Experiments

Transparent man-made porous media, also known as micromodels, are a widely used exploration tool in the field of two-phase flow in porous media (Alireza and Sohrabi in Soc Petrol Eng 166435, 2013; Bondino et al., in International symposium of the society of core analysts held in Napa Valley, California, USA, 2013) to enhance the comprehension of oil recovery mechanisms at pore-scale. Although they have more often been used as qualitative visualization tools to explore the elementary physicochemical features of a given flow mechanism, their utilization as a quantitative tool is interesting especially in industrial context, where they represent an easy and low-cost screening tool for complex recovery mechanisms (low salinity waterflooding, polymer flooding, etc). However, the repeatability of these experiments and thus the possibility to derive quantitative conclusions from them appears not to be investigated in the literature in our field of study. In this work, we explore the dispersion of data such as capillary desaturation curves and secondary waterflood recoveries using micromodels of different sizes and different pore patterns from our laboratory and from an external one. Using datasets with low sampling (low number of repeats of an experiment) and with very large sampling, we document the type of data dispersion, we analyze its reasons and we verify to which extent truly quantitative conclusions can be drawn from these datasets. Our study demonstrates that at low sampling drawing quantitative inferences from our datasets is questionable due to the large uncertainty of the produced data.