Determination of Dead-Oil Wetting and Adhesive Forces on Carbonate

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Determination of Dead-Oil Wetting and Adhesive Forces on Carbonate Rocks using Colloidal-Probe AFM Jehad Abed, Cyril Aubry, Mouna Zaidani, Nabil El-Hadri, Rajakumar Devarapali, and Mustapha Jouiad Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01941 • Publication Date (Web): 30 Jul 2018 Downloaded from http://pubs.acs.org on August 2, 2018

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Determination of Dead-Oil Wetting and Adhesive Forces on Carbonate Rocks using Colloidal-Probe AFM Jehad Abed*, Cyril Aubry, Mouna Zaidani, Nabil El Hadri, Rajakumar Devarapalli and Mustapha Jouiad* Mechanical and Materials Engineering, Masdar Institute of Science and Technology, A part of Khalifa University of Science and Technology, 54224, Abu Dhabi, UAE.

ABSTRACT: In the attempt to unveil the effects of carbonate reservoir surface interactions with crude oil on its wettability, novel in-situ atomic force microscopy experiments (Force Volume) were performed to map the adhesion forces between the dead crude oil and carbonate rocks rich with natural minerals, Calcite and Dolomite. In this sense, carbonate samples were submerged in a fluid cell filled with deionized water to minimize the effect of the surrounding environment and account only for the interactions involving the AFM probe functionalized with oil and the carbonate surface. Besides, wettability alteration on carbonate was determined through contact angle measurements using both sessile drop technique and in-situ environmental scanning electron microscope (ESEM). These measurements were carried out with respect to both water and oil at various roughness induced by the sample surface modifications. Our results show that the obtained contact angle is sensitive to both the mineralogy and the surface roughness of the

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rock sample. Indeed, Dolomite-rich regions exhibit a more hydrophilic nature than Calcite-rich regions for all investigated roughness (1-5 µm), where the initial contact angle was increased linearly by a factor of 2.5. In the contrast, no significant change in contact angle was measured in oil medium for both regions. In addition, quantitative force curves and adhesion force maps at various locations of the rocks sample show 2 to 3 times lower adhesion forces between dead oil and Calcite-rich regions (32 nN) when compared to Dolomite-rich regions (104 nN). These inputs could help the oil industry to consider the wettability alteration of carbonate to develop innovative methods for enhanced oil recovery (EOR).


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1. INTRODUCTION

While fossil fuels are finite resources of energy that relatively are depleting rapidly, crude oil currently accounts for more than one third of the total global energy consumption making it difficult, at least in the near future, for alternative resources of energy to meet the growing global consumption especially in the transportation sector1–3. While naturally extracted crude oil, under its own flow pressure, only represents 10% of the oil reserved in a typical reservoir, secondary recovery techniques such as water injection are used to drive oil and extract an additional 10% to 30% of the oil leaving more than 60% of the oil in place unexploited4. With much of the feasibly extracted (primarily and secondarily recovered) oil was already produced from oil fields all over the world and the discovery of new oil fields became quite limited, producers are left with more challenges and fewer commercial solutions to maintain oil productivity5. Therefore, enhanced oil recovery (EOR) techniques such as chemical flooding are found to be effective in recovering up to 35% of the oil from non-conventional reservoirs6. Chemical flooding consists of adding for instance polymers to water to reduce viscous fingering and to improve volumetric sweep. This is accomplished by enhancing the displacement efficiency, the interfacial tension between oil and water is reduced (Surfactants are usually used for this objective). In addition, by controlling the mobility of fluids, the mobility contrast between water and oil is reduced via increasing the viscosity of the injected water5,6. The current research is a part of a project aiming to increase the efficiency of EOR in carbonate reservoirs. Pragmatic approach to predict and optimize oil recovery from carbonate reservoirs is very challenging due to the complex nature of the rocks. In real reservoir conditions, surface wettability and adhesion forces are altered by the changing chemical composition, inherent morphology and bulk properties of the carbonate rock surface. It is widely common to prepare


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special smooth and pure substrates, such as Calcite crystals, for characterization to reduce compositional complexity and roughness effects7–9. While this simplifies experimental conditions, it may lead to question the predictive capabilities of the approach and whether it provides a more realistic description of actual crude oil-carbonate rocks interaction10. With the great versatility in structure and composition of the rocks, it is quite difficult to understand the interfacial interaction between oil and the several mineral phases (mainly Calcite and Dolomite) present at the surface of the rock.

For that purpose, we use static contact angle (CA)

measurements using sessile drop technique and in-situ environmental electron microscope (ESEM) to evaluate wettability at microscale in one hand, and colloidal-probe atomic force microscopy (AFM) in Force Volume (FV) mode to map adhesive forces at nanometre resolution on carbonate surfaces in the other hand. Surface wettability can be assessed using contact angle measurements, which is the most common technique that can provide a representative approach to study fluid-surface interactions11,12. However, contact angle measurements alone fail to provide a comprehensive way to investigate actual crude oil-carbonate system due to the limited resolution (microscale), and the difficulty in resolving nanoscale interactions and consistent results13. Besides, AFM measurements amended by the topographic information, can determine the force interaction between the tip and the sample at the nanoscale regime with respect to their surface properties. This effectively contributes in quantifying the interfacial interaction and the prospective intrinsic surface energy of the present phases in the rocks

7,14

. This combined

approach allows determining the wetting and the adhesive forces quantitatively without averaging over the various heterogeneous phases present on the rock surface 15. This provides a more realistic representation of the measured forces and interaction behaviour between dead oil and minerals in the rock.


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Numerous similar studies using AFM have demonstrated a reliable approach to better understand the wettability and the oil-mineral adhesive forces at the macro and nanopores scale. For instance, Stipp’s group used AFM in Chemical Force Mapping (CFM) mode16 to accurately study wettability alteration of sandstone17 and calcite surfaces under ionic substitution7 and in different salinities18,19. CFM is a widely used technique that estimates wettability changes and oil-mineral adhesion forces by utilizing hydrophobic (CH3-terminated) functionalized probes to simulate tiny oil droplets on the AFM tip. Despite CFM being a powerful technique, it does not provide a direct evaluation of real crude oil-mineral adhesive forces. Hence, utilizing colloidalprobe AFM20–22 the crude oil (AFM probe) and carbonate rock surfaces (substrate) in the system can be presented, then force curves on different locations on the substrate are collected to probe the force interaction between the AFM probe and the substrate as a function of separation in few nanometres and piconewtons resolution.

2. EXPERIMENTAL SETUP

2.1 Sample Preparation. Carbonate samples were collected from selected Abu Dhabi, UAE reservoir (Bu Hasa) with known macroscopic flow properties. Then, specific sample preparation workflow was established to maintain reproducible results and validate the measurements. Prior to any experiment, the samples were appropriately cleaned and polished to eliminate the influence of contaminants and residual surface roughness on the results. The following protocol was applied to all performed measurements: the as-received carbonate rock samples were cut from the bulk specimen of about 2 mm thickness (1 inch in diameter) using Bhuler™ diamond disc cutter and then they were ultrasonicated in deionized (DI) water for about one minute to remove debris and broken fragments from cutting process.


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Afterwards, they were thinned carefully with different grit size abrasive SiC polishing papers 1000, 1500, 2000, 4000 and later with diamond paste down to 0.25 µm, while ultrasonicated in DI water for every polishing step and at last, they were cleaned in Iso-Propanol to remove any contamination from polishing processes. To remove remaining solvents from sample preparation, the samples were boiled in hot distilled water for 5 minutes. Then, the samples were put in desiccator for few hours until their weight is stabilized to ensure complete drying. For surface imaging experiments, the surface was coated with a thin layer of conducting metal (Au/Pd) using sputtering system PECS from Gatan™. The microstructure and minerology were monitored and assessed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS).

2.2 Oil-functionalized Colloidal Probes. The in-house preparation and oil functionalization of AFM colloidal-probes protocol were controlled manually using Nano-ObserverTM AFM equipped with a movable camera for precise observation and manipulation. A non-coated Sibased ACT-W AFM probe is used (APPNANOTM) as shown in Figure 1(b) and Figure 1 (c), the stiffness of the cantilever is between 13-77 N/m. To prepare the probe, a solution of dispersed Silica microbeads has been dried for one day at room temperature on top of a smooth Mica substrate as illustrated in Figure 1(a). Then, an individual 20-40 µm diameter Silica microbead was attached to the end of the cantilever using epoxy resin. As can be seen from the SEM images in Figure 1(d) and (e), an approximately 20-µm-radius-bead seems attached to the cantilever and the surface of the bead is smooth. The epoxy shown in the titled image in Figure 1(e) is just covering the base of the Silica microbead while the other edge of the bead is cleared for AFM measurements. After repeating the manufacturing protocol several times, we can claim that the preparation


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method is reliable and produces well-attached smooth Silica microbeads. The size and the stiffness of the beads were chosen specifically for AFM experiments with carbonate rocks (hard surfaces); the relatively big size of the beads allows larger surface area interaction with the surface of the rock which is significant for a more precise quantification of the adhesion forces. The probe is immersed into dead oil, immediately before mapping adhesion forces on Carbonate rocks, creating a wet-oil probe. Overtime the oil will pull off the wet-oil probes and the probe will need to be changed more frequently from one experiment to another. This could lead to major inconsistencies in the obtained results. This behaviour was previously reported by Basu and Sharma who defined a critical pressure where wet oil disjoints in the water cell

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. Thus, it was necessary to preserve the dead oil on the probe for long-term

experiments. Dickinson et al showed that drying wet-oil probes will evaporate the nonpolar volatile portion of the crude oil while keeping the polar content 22. This forms a robust dry oil layer on the colloidal probe suitable for durable aqueous experiments. In our experiments, we prepared dry probes as shown in Figure 1(f). The quality of oil coating varies significantly from one experiment to another, the AFM probe was placed on a glass slide then a drop of oil was released on top of the cantilever to cover it entirely and ensure homogenous coverage of oil on the surface of the Silica microbead. The AFM probe on the glass slide was then placed in the oven and heated at 50 °C for 48 hours. The produced dry-oil probe was investigated using ESEM as shown in Figure 1(g), the bead is covered by a conformal layer of dry oil. Before using oil-functionalized probes in AFM experiments, it is very important to test the followed oil-functionalizing protocol using the following procedures. First, Raman spectra were collected from various points of the sample to confirm homogenous coating of the oil.


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As can be seen in Figure 2(a), the sharp first-order peak at 520 cm-1 and broad second-order peak between 900-1000 cm-1 are the signature of Raman scattering characteristic peaks from Si in the bare Silica microbead

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. When the probe is functionalized with crude-oil, the

background baseline in the Raman spectrum (highlighted in yellow) is altered due to oil fluorescence. This change indicates the presence of oil on the surface of the Silica microbead. Raman mapping the surface of the bead as shown in Figure 2(b), shows conformal coating of crude oil on the whole Silica microbead surface. The wet-oil probe was then utilized for standard force spectroscopy measurements on a smooth freshly cleaved Mica sample in standard fluid cell filled with DI water (volume 2 mL) to reduce surface capillary forces in humid air (thin film of water forming on the surface under atmospheric conditions)

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. The

wet-oil probe force measurements were carried out using BrukerTM Dimension Icon AFM for both functionalized and non-functionalized (w/o crude oil) colloidal-probe as shown in Figure 2(c)-(f). Mica was selected for our testing procedure, it can be mechanically exfoliated to produce a clean and flat surface to avoid roughness effects. The retract force curves for both types of probes were collected as shown in Figure 2(c) and (d), alteration in the behavior of the force curves is tracked and used as an indication of oil coating (functionalization). The adhesion between functionalized oil probe to Mica in presence of water is expected to be dependent on electrostatic forces and short-range Van Der Waals forces or the interplay of both. Typically, researchers used the change in measured force curves and adhesion forces as an indirect indication to infer successful modification of the AFM probe26. In the case of non-functionalized probes (Bare Silica microbead), the interaction was repulsive and no adhesion to the surface of Mica was observed while decompressing. The interaction shown in Figure 2(c) is typical for Silica on Mica unless the


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surface of the oxide is modified. When the Silica microbead is functionalized with oil, the behavior of the force curve was altered as shown Figure 2(d). The presence of adhesion (negative force values) when the functionalized probe was compressed against Mica indicates that a significant area of the bare Silica microbead was covered by oil as shown in Figure 2(d). This change in force curve behavior is a proof of a good modification of the Silica surface with crude oil as it indicates that the adhesion was entirely caused by the presence of crude oil on the surface of the Silica microbead 27. Force measurements between functionalized probes and carbonate rock samples were carried out before each set of AFM adhesion measurements. The collected force curves between the colloidal-probe and Mica while immersed entirely in water were used to verify the modification of Silica microbead. If characteristic force curve behavior was obtained similar to that shown in Figure 2(d), then these probes were used to conduct adhesion measurements. In addition, the effect of electrostatic forces as a function of salinity on the approach force curves for both types of probes and Mica was studied. Force curves for both probes were recorded in water solutions at different salinity concentrations 1, 10 and 100 mMol of NaCl on different sites of the substrate within a well-sealed water cell as in Figure 3(a). In Figure 2(e), force curves are dependent on the concentration of the solution; as the concentration of the solution is increased the decay constant of the curve is decreased due to the screening effect caused by the presence of positively charged species in the solution 28. In the case of wet-oil probes as in Figure 2(f), the force curves are independent of solution concentration and the repulsion is linearly correlated with approach distance. This linearity is attributed to the compression of the oil layer on the Silica microbead when pushed against the substrate 29

. Hence, the thickness of the oil layer can be estimated from the linear region of the curve to


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be around 50 nm. In general, the dependency of force curves on solution concentration can be used as an indication for oil functionalization.

2.3 Contact Angle Measurements. The static contact angle (CA) was measured at different locations on the solid surface of the sample using a goniometer (DM-501, Kyowa™ Interface Science Co., Ltd). A water microdroplets of 0.2 µL were impinged at different sites on the surface and the corresponding CAs were measured using optical microscope equipped with CCD camera and analyzed using ImageJTM software. The CA is measured at the equilibrium state between the droplet, the solid surface, and the surrounding gas (Air). Similarly, the microscopic CA was evaluated using in-situ using ESEM experiments equipped with Gaseous Secondary Electron Detector (GSED) and Peltier (heating/cooling) stage to control water condensation on solid substrates. The Peltier stage is attached to control the temperature of the samples inside the SEM chamber. Where, partial pressure inside the chamber is controlled by the SEM chamber pump. The condensation inside the chamber is reversible process, hence droplets’ formation can be controlled by evaporation and condensation. Quanta 250 FEG (FEITM) was used to observe in real-time the evolution of the droplets on the solid surface to measure the corresponding CAs 30,31. In our experiments, the stage was cooled and maintained at a temperature of 1°C and the pressure of the chamber was gradually increased up to 800 Pa to allow condensation on the solid surface. Droplets were formed on the solid surface by increasing the chamber pressure in 50 Pa steps. Imaging of water droplets was done at constant pressures and an accelerating voltage of 10 kV.

3. RESULTS AND DISCUSSION


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3.1 Mineralogy and Microstructure. Our carbonate rock samples possess two distinct phases (can be distinguished by naked eye): Calcite-rich and Dolomite-rich phases as can be shown in Figure 3(a) and (b). The Calcite-rich phases exhibit two distinct regions, one is highly dense region and the other is porous region with 15-20 µm edge size as shown in Figure 3(d). The high magnification images demonstrate the presence of fine sub-micron pores within the crystals. Red arrows show the pores within the grain and the blue ones show pores between grains. The minerology of the phase was determined using EDS. Initially spot EDS analysis was performed at different locations to identify chemical elements and then high-resolution mapping was carried out to determine concentrations. The elemental maps as demonstrated in Figure 3(f) indicates the presence of abundant Ca and a low fraction of Mg (6% to 10%). Other elements were mapped such as S and O (not shown in the figure). Similarly, the surface morphology of Dolomite-rich phases was imaged using SEM. This phase shows three major morphologies as seen in Figure 3(c): pyramid like crystals arranged along the surface of island, fine grain cubic crystals within the island and dense solid crystals. Further EDS studies were performed on all three crystal regions to identify chemical elements. As shown in Figure 3(e) Dolomite-rich regions are rich of Mg (70% - 80%) with a relatively smaller concentration of Ca.

3.2 Wettability. Carbonate rocks found in reservoirs are complex and heterogeneous structures as explained in the previous section. Each constituent (Ca or Mg) has different wettability characteristics making it difficult to describe the wetting behavior of the composite rock. In addition, surface roughness and morphology bring up further complexity in evaluating the wettability of the carbonate rock. Figure 4(a) shows the static contact angle of water microdroplets for Calcite-rich and Dolomite-rich regions with respect to induced surface roughness. In general, it can be seen that the contact angle at Calcite-rich regions is higher than what is obtained at Dolomite-rich regions. Therefore, regions rich with Mg content are more hydrophilic. In both samples, applied roughness (0.25, 1, 2, 3, 4 and 5 µm) was induced on the surface of the sample using


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diamond liquid and SiC abrasive paper. As shown in the figure, contact angle follows a parallel linear trend for both Calcite-rich and Dolomite-rich regions when the induced roughness is increased. These results indicate that the presence of more pores induced by the application of roughness, traps air and increases the contact angle between water and the surface of the sample32. However, there is one data value which doesn’t follow the trend obtained at 0.25 µm roughness, the CA values for both samples (28° for Calcite-rich, 22° for Dolomite-rich) are higher than the values obtained at 1 µm (23° for Calcite-rich, 12° for Dolomite-rich). This is because at 0.25 µm porosity of the surface is significantly reduced compared to 1 µm. Figure 4(c) and (d) show water droplets on rock surface obtained by in-situ experiments for Calcite-rich and Dolomite-rich regions. These results will help to build a multiscale correlation between the contact angle values obtained by sessile drop method (macroscopic scale) and ESEM (microscopic scale). Similarly, in-situ results show that the Calcite-rich regions had higher contact angle values (86° ±6°) than those obtained for the Dolomite-rich regions (73° ±13°). Despite the different environment and droplet size used in ESEM, both experiments confirmed that Dolomite-rich regions are more hydrophilic than Calcite-rich regions. Figure 4(b) shows the static contact angle of oil obtained for Calcite-rich and Dolomite-rich regions with respect to applied roughness. When compared to the results obtained with water, the evolution of the contact angle of oil with respect to roughness is quite different. For both regimes, when applied roughness increases, contact angle is relatively constant with a value around 20° making it difficult to distinguish between the oleophilicity of the two regions. Moreover, oil is more viscous than water therefore surface adhesion and interfacial


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characteristic is more significant than roughness micro effects. Hence, investigating the interfacial adhesion between crude oil and carbonate rock at the nanoscale using colloidalprobe AFM is crucial to understand wettability and adhesion at the macroscopic scale20. 3.3 Adhesion Force Spectroscopy. After testing the manufacturing and functionalization of the AFM probes protocol on Mica and treating the probes in the furnace, the adhesion between dry-oil probes and different regions on the as-obtained carbonate rocks was examined. The carbonate rock sample went through the same polishing and cleaning process, which was explained earlier in this work, before immersing it in a well-sealed liquid cell as in Figure 3(a). The liquid cell is filled with DI water to eliminate the contribution of ionic species on electrostatic forces. Typical adhesion measurements were carried on each of the two distinct regions using Force Volume AFM technique. The force volume technique allows the collection of force curves while scanning the topography of the sample. The absolute minimum values from each of these generated force curves will then be used to generate force adhesion maps. Figure 5 shows a typical set of measurement data, force adhesion maps are collected using dry-oil probes within the indicated square regions (Blue for DolomiteRich region and Green for Calcite-rich region) which are limited to an area of 80 µm X 80 µm due to stage movement range restriction. The force curves were taken at a scan rate of 0.3 Hz with a typical ramp size of 1400 nm; which converts to an approach and retract speeds of 1 µm/s. Operating at such slow scan rate and approach speed is required to measure adhesion in absence of any hydrodynamic effects between oil and water. Figure 5(a) and (b) show 80 µm X 80 µm adhesion maps formed by 64 X 64 force-distance curves collected at different sites generating a total of 4096 force curves per each adhesion map. When comparing the two adhesion maps it can be seen that the adhesion between


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crude-oil and the Dolomite-rich region is considerably higher than the Calcite-rich region. The measured adhesive forces were normalized by the radius of the used Silica microbeads (18.5 µm). The result is statistically quantified as shown by the histograms in Figure 5(c) and (d). Knowing that each of the two regions doesn’t purely consist of one of the two minerals distinctively (Ca or Mg) but rather a commensurate mixture of both, it is believed that adhesion forces lower than 2 nN/µm in both histograms correspond to the Ca mineral only where adhesion forces higher than the stated value corresponds to the Mg mineral. Figure 5(e) shows a sample force-separation curves obtained for dry-oil probe interacting with Calcite-rich and Dolomite-rich regions. The well depth for Dolomite-rich curve indicates higher adhesion force. This was quantitively confirmed by repeating the same set of measurements at different locations on the carbonate rock surface as shown in Figure 5(f). Also, it can be concluded that the mean adhesion force of oil measured on Dolomite-rich regions (5.23 nN/µm ±0.21) is 2-3 times more than the one for Calcite-rich regions (1.61 nN/µm ±0.46). Figure 6 shows density plots of approach and retract force curves on Dolomite-rich and Calcite-rich regions. A selected 256 force-separation curves from adhesion maps were plotted in each of the four sub-figures. In the case of approach curves, there was a non-linear interaction from 350 nm – 200 nm caused by the soft repulsion between the coated oil layer on Silica microbeads and rock surface until contact as shown in Figure 6(a) and (b). Since the exact oil-functionalized AFM probe was used for both experiments, it is expected to preserve the thickness of the oil layer assuming no significant wear happened between both experiments. This repulsion is expected to increase dramatically and linearly after oil contact due to hard contact between Silica microbead surface and the rock surface in the so-called


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constant compliance region. In the case of Calcite-rich and Dolomite-rich regions, the approach non-linear behavior of the curves varies due to the deformation of the oil layer when pushed against the solid surface. This variance might be caused by the interaction between oil and trapped water due to the hydrophilicity difference between the two present phases 33,34 or local roughness. Overall, both of the approach force curves in Figure 6(a) and (b) represents a reliable and reproducible quantification of interaction between dead oil and Dolomite/Calcite-rich phases. This quantitively determined interaction is vital to compare adhesion forces on different samples. When comparing the density plots of retract force curves between Dolomite-rich and Calciterich regions as in Figure 6(c) and (d), it can be clearly seen that Dolomite-rich curves exhibits a denser adhesive behavior as indicated by negative force values. A single force curve for both regions is shown in the inset of the figures. Although the adhesion force values varied in the Dolomite-rich region from position to another, the general trend conforms with higher distribution of adhesive forces between crude oil and dolomite when compared to calcite.

4. CONCLUSIONS

The protocol developed in this work allows direct quantification and statistical comparisons of wettability and adhesive forces of dead crude oil on complex surfaces such as carbonate rocks extracted from oil reservoirs. Macroscopic and microscopic contact angle along with functionalized colloidal-probe AFM experiments revealed that Dolomite-rich regions are more oleophilic than Calcite-rich regions because of mineral constitution and surface roughness. Customized colloidal AFM probes were prepared In-house and functionalized with oil for force


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spectroscopy measurements on hard carbonate rocks. Force spectroscopy measurements on Mica in DI water and NaCl solutions with different concentrations confirmed oil coating and were used to estimate oil film thickness. The measured contact angles using sessile drop technique and in-situ environmental ESEM indicated that Dolomite-rich regions are more hydrophilic than Calcite-rich regions and the contact angle increases linearly with increased applied roughness for both regions. Although roughness plays a crucial role in the values of water contact angle, it has little influence on the values of oil contact angle. Adhesion force maps consisting of 64 x 64 force curves each were collected from six different locations on the sample to allow better quantification of adhesion behavior. Adhesion forces measured at multiple sites on Dolomiterich regions were at least two times larger than the ones obtained on Calcite-rich regions. Force curves measured at Dolomite-rich regions encountered more deformation than Calcite-rich regions because of local roughness and surface morphology difference. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *Email: [email protected] ACKNOWLEDGMENTS This work is based on experimental investigations performed in the project: “Pore-scale Wettability and Three-Phase Relative Permeability Characterization for WAG-EOR of Carbonate Reservoirs” funded by ADNOC under ADNOC-Masdar Institute contract #8443000185.


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Seyyedi, M.; Sohrabi, M. Investigation of Rock Wettability Alteration by Carbonated Water through the Contact Angle Measurements Investigation of Rock Wettability Alteration by Carbonated Water through the Contact Angle Measurements Mojtaba Seyyedi and Mehran Sohrabi. 2015.

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Bikkina, P. K. Contact Angle Measurements of CO2-Water-Quartz/Calcite Systems in the Perspective of Carbon Sequestration. Int. J. Greenh. Gas Control 2011, 5 (5), 1259–1271.

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Sun, H.; Di, D.; Tao, G.; Vega, S.; Li, K.; Liu, L.; Belhaj, H. Carbonate Rocks: A Case Study of Rock Properties Evaluation Using Multi-Scale Digital Images. Soc. Pet. Eng. SPE Abu Dhabi Int. Pet. Exhib. Conf. 2017 2017, 2017–Janua.


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Chau, T. T. A Review of Techniques for Measurement of Contact Angles and Their Applicability on Mineral Surfaces. Miner. Eng. 2009, 22 (3), 213–219.

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Mohammed, M.; Babadagli, T. Wettability Alteration: A Comprehensive Review of Materials/Methods and Testing the Selected Ones on Heavy-Oil Containing Oil-Wet Systems. Adv. Colloid Interface Sci. 2015, 220, 54–77.

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Shedid, S. A.; Ghannam, M. T. Factors Affecting Contact-Angle Measurement of Reservoir Rocks. J. Pet. Sci. Eng. 2004, 44 (3–4), 193–203.

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Eichmann, S. L.; Burnham, N. A. Calcium-Mediated Adhesion of Nanomaterials in Reservoir Fluids. Sci. Rep. 2017, 7 (1), 1–9.

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Boyd, R. D.; Bargir, S.; Jefferson, B. Crystals With Macroscale Contact Angle and Scaling Characteristics . a B. 2006, 1, 768–771.

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Hilner, E.; Andersson, M. P.; Hassenkam, T.; Matthiesen, J.; Salino, P. A.; Stipp, S. L. S. The Effect of Ionic Strength on Oil Adhesion in Sandstone - The Search for the Low Salinity Mechanism. Sci. Rep. 2015, 5, 1–9.

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Hassenkam, T.; Skovbjerg, L. L.; Stipp, S. L. S. Probing the Intrinsically Oil-Wet Surfaces of Pores in North Sea Chalk at Subpore Resolution. Proc. Natl. Acad. Sci. 2009, 106 (15), 6071–6076.

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Dickinson, L. R.; Suijkerbuijk, B. M. J. M.; Berg, S.; Marcelis, F. H. M.; Schniepp, H. C. Atomic Force Spectroscopy Using Colloidal Tips Functionalized with Dried Crude Oil: A Versatile Tool to Investigate Oil–Mineral Interactions. Energy & Fuels 2016, 30 (11), 9193–9202.

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Basu, S.; Sharma, M. M. Measurement of Critical Disjoining Pressure for Dewetting of Solid Surfaces. J. Colloid Interface Sci. 1996, 181 (2), 443–455.

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Colak, A. Measuring Adhesion Forces between Hydrophilic Surfaces with Atomic Force Microscopy Using Flat Tips; 2013.

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Reginald Thio, B. J.; Lee, J. H.; Meredith, J. C.; Keller, A. A. Measuring the Influence of Solution Chemistry on the Adhesion of Au Nanoparticles to Mica Using Colloid Probe Atomic Force Microscopy. Langmuir 2010, 26 (17), 13995–14003.

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Energy & Fuels

Figure 1. a) A schematic demonstrating the manufacturing procedure of our wet-oil AFM probes: (1) Drop-casting a solution of Silica microbeads on a Mica substrate and drying it overnight under room temperature. (2) Dipping the AFM probe in a small droplet of wet epoxy on Mica. (3) Before the epoxy dries, the cantilever is manipulated to land on an isolated Silica microbead for attachment. (4) The probe is left overnight under room conditions to dry the epoxy and then a drop of crude oil is impinged onto the cantilever. (5) Functionalized wet-oil probe is ready. b) ESEM image of AFM probe (b) and (c) before bead attachment, (d) and (e) after bead attachment. (f) Preparation procedure of dry-oil probes (g) Tilted ESEM image of the prepared dry-oil probe.


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Figure 2. (a) Raman spectrum of the functionalized Silica microbead functionalized with crude oil (b) Corresponding Raman map Retract force curves of (c) Non-functionalized colloidal probes (d) Wet-oil probes on Mica. Approach force curves of (e) Nonfunctionalized colloidal probes and (f) Wet-oil probe in 3 different concentrations of NaCl solution 1, 10 and 100 mMol.


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Page 23 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 3. Optical images of the carbonate rock sample (a) in the sealed liquid cell used for AFM measurements in water, inset is a magnified image of the sample. (b) magnified image of the surface of the sample, black domains are Dolomite-rich regions while white domains are Calcite-rich regions. SEM micrographs of (c) fractured Dolomite-rich regions. Highlights show the two distinct features from two different regions. (d) the fractured topography of Calcite-rich regions, the magnified regions show the morphology at different locations while high magnified images show the presence of intergranular pores and pores within the grains as indicated by red and blue arrows respectively. EDS elemental maps of (e) Dolomite-rich regions (f) Calcite-rich regions, showing the elemental distribution of Mg and Ca (Mg is a signature of Dolomite).


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Figure 4. Static contact angle of (a) Water (b) Oil microdroplets on Calcite-rich and Dolomite-rich regions against applied roughness on the surface. Insets in (a) show optical micrographs of sessile drop measurement. In-situ contact angle measurement carried inside ESEM for (c) Calcite-rich and (d) Dolomite-rich regions.


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Page 25 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 5. Typical data set from AFM adhesion measurements. adhesion maps for (a) Dolomite-rich and (b) Calcite-rich regions. The adhesion maps are collected from a square area of 80 µm x 80 µm. For each measurement, 4096 force curves were collected forming a 64 x 64 pixels adhesion maps and histograms of measured adhesion values as in (c) and (d) for Dolomite-rich and Calcite-rich regions correspondingly. (e) Typical force-separation curves obtained at Calcite-rich and Dolomite-rich regions. (f) Mean adhesion force at three different positions on the samples. All force values are normalized by the radius of the Silica microbead.


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Figure 6. A series of force-separation curves from both (a, c) Dolomite-rich region and (b, d) Calcite-rich region. Approach force curves. Adhesion forces are measured by taking the absolute minimum value of retract force curves shown in (c, d).


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Page 27 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 1. a) A schematic demonstrating the manufacturing procedure of our wet-oil AFM probes: (1) Dropcasting a solution of Silica microbeads on a Mica substrate and drying it overnight under room temperature. (2) Dipping the AFM probe in a small droplet of wet epoxy on Mica. (3) Before the epoxy dries, the cantilever is manipulated to land on an isolated Silica microbead for attachment. (4) The probe is left overnight under room conditions to dry the epoxy and then a drop of crude oil is impinged onto the cantilever. (5) Functionalized wet-oil probe is ready. b) ESEM image of AFM probe (b) and (c) before bead attachment, (d) and (e) after bead attachment. (f) Preparation procedure of dry-oil probes (g) Tilted ESEM image of the prepared dry-oil probe. 101x90mm (600 x 600 DPI)


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. (a) Raman spectrum of the functionalized Silica microbead functionalized with crude oil (b) Corresponding Raman map Retract force curves of (c) Non-functionalized colloidal probes (d) Wet-oil probes on Mica. Approach force curves of (e) Non-functionalized colloidal probes and (f) Wet-oil probe in 3 different concentrations of NaCl solution 1, 10 and 100 mMol. 101x106mm (600 x 600 DPI)


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Page 29 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 3. Optical images of the carbonate rock sample (a) in the sealed liquid cell used for AFM measurements in water, inset is a magnified image of the sample. (b) magnified image of the surface of the sample, black domains are Dolomite-rich regions while white domains are Calcite-rich regions. SEM micrographs of (c) fractured Dolomite-rich regions. Highlights show the two distinct features from two different regions. (d) the fractured topography of Calcite-rich regions, the magnified regions show the morphology at different locations while high magnified images show the presence of intergranular pores and pores within the grains as indicated by red and blue arrows respectively. EDS elemental maps of (e) Dolomite-rich regions (f) Calcite-rich regions, showing the elemental distribution of Mg and Ca (Mg is a signature of Dolomite). 96x60mm (600 x 600 DPI)


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. Static contact angle of (a) Water (b) Oil microdroplets on Calcite-rich and Dolomite-rich regions against applied roughness on the surface. Insets in (a) show optical micrographs of sessile drop measurement. In-situ contact angle measurement carried inside ESEM for (c) Calcite-rich and (d) Dolomiterich regions. 102x69mm (600 x 600 DPI)


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Page 31 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 5. Typical data set from AFM adhesion measurements. adhesion maps for (a) Dolomite-rich and (b) Calcite-rich regions. The adhesion maps are collected from a square area of 80 µm x 80 µm. For each measurement, 4096 force curves were collected forming a 64 x 64 pixels adhesion maps and histograms of measured adhesion values as in (c) and (d) for Dolomite-rich and Calcite-rich regions correspondingly. (e) Typical force-separation curves obtained at Calcite-rich and Dolomite-rich regions. (f) Mean adhesion force at three different positions on the samples. All force values are normalized by the radius of the Silica microbead. 101x98mm (600 x 600 DPI)


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. A series of force-separation curves from both (a, c) Dolomite-rich region and (b, d) Calcite-rich region. Approach force curves. Adhesion forces are measured by taking the absolute minimum value of retract force curves shown in (c, d). 99x65mm (600 x 600 DPI)


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Determination of Dead-Oil Wetting and Adhesive Forces on Carbonate

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