Interfacial Tension and Contact Angle Determination in Water-sandstone Systems with Injection of Flue Gas and CO2

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A26

Interfacial Tension and Contact Angle

Determination in Water-sandstone Systems with

Injection of Flue Gas and CO2

N. Shojai Kaveh* (Delft University of Technology), E.S.J. Rudolph (Delft University of Technology), W.R. Rossen (Delft University of Technology), P. van Hemert (Delft University of Technology) & K.H. Wolf (Delft University of Technology)

SUMMARY

Carbon capture and storage (CCS) has the potential for reducing CO2 emissions to the atmosphere. This option includes storage strategies such as CO2 injection into deep saline aquifers, depleted oil and gas reservoirs, and unmineable coal seams. This process is largely controlled by the interactions between CO2, the reservoir fluid and reservoir rock. In particular, the wettability of the rock matrix has a strong effect on the distribution of the injected CO2 into geological formations.

In this study, the wetting behavior of Bentheimer sandstone slabs and CO2 and/or flue gas is investigated by means of contact-angle measurements. In addition, the interfacial tension between CO2 and/or flue gas and connate water was determined. The experiments were conducted in a pendant-drop cell, adapted to allow captive-bubble contact-angle measurements and performed at a constant temperature of 318 K and pressures varying between 0.2 and 15 MPa, typical in-situ conditions.

The experimental contact angle measurements show that the Bentheimer sandstone/water system is (and remains) water-wet even at high pressures with CO2 and/or flue gas injection. The determined data of the contact angle of the water–sandstone system demonstrate a strong dependence on the bubble size and surface roughness with CO2 and flue gas injection.

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IOR 2013 – 17th European Symposium on Improved Oil Recovery St. Petersburg, Russia, 16-18 April 2013

1. Introduction

Carbon capture and storage (CCS) has the potential to reduce CO2 emissions from the atmosphere

when hydrocarbons and coal are burned. This option includes storage strategies such as CO2 injection

into deep saline aquifers (Basbug et al. 2007, Chadwick et al. 2007, Ofori and Engler 2011), depleted oil and gas reservoirs (Arts et al. 2008, Arts et al. 2012, Damen et al. 2005, Meer et al. 2010, Stein et al. 2010, Velasquez et al. 2006), and unmineable coal seams (Bergen et al. 2009, Bergen et al. 2006, White et al. 2005).

In deep saline aquifers, CO2 can be stored as free CO2 in rock pore spaces (Structural Trapping),

chemically bonded with components in the rock (Mineral Trapping) or stored in reservoir water as a result of its solubility in water (Solubility Trapping) (Basbug et al. 2007). CO2 storage in depleted or

almost depleted gas reservoirs is an attractive option for CO2 sequestration because of the acquired

knowledge of the reservoir during the exploitation stage, available underground and surface infrastructure, and the opportunity to enhance gas recovery (EGR) (Li et al. 2006).

In general, the success of the CO2 storage in hydrocarbon reservoirs and in deep saline aquifers is

largely controlled by gas-liquid-rock interfacial interactions(Arendt et al. 2004, Yang et al. 2008). The relation between the major interfacial interactions - interfacial tension, capillarity and wettability - are represented by the Young-Laplace equation:

. , .

, (1)

where Pc is the capillary pressure, γw,CO2 is the connate water-CO2 interfacial tension, R is the effective

radius, and θ is the contact angle, which is related to reservoir wettability.

In reservoir engineering, the wettability has been recognized as one of the important factors determining the residual oil saturation, capillary-pressure and relative-permeability functions (Anderson 1986, Anderson 1987, Hirasaki 1991, Morrow 1990). However, the wettability of the reservoir rock is basically determined by complex interfacial interactions between the rock that is composed of a wide variety of minerals, and the reservoir fluids that occupy the highly irregular pore space. Apart from the pore-size distribution and morphological description of the pore space of the reservoir rock, also the capillary pressure and capillary-sealing efficiency depend on 1) the liquid/ CO2 interfacial tension (IFT) and 2) the contact angle at storage conditions which might be sensitive

to pressure (Chiquet et al. 2007).

Commonly, the wettability of a rock-aqueous phase-fluid system (Figure 1) is characterized by means of the contact angle as presented in Young’s equation:

γ cosθ γ γ , (2)

Here , and are the interfacial or surface tensions between the aqueous phase and the gas phase, the solid and the gas phase, and the solid and the aqueous phase, respectively; θ is the contact angle and, according to the common convention, is determined with respect to the denser fluid phase. Commonly, the product γ cosθ is referred to as the adhesion force (Adamson and Gast 1997). In geological storage of CO2, the adhesion force is used for the calculation of the capillary number, and

through that property the fluid distribution in a reservoir is determined (Yang et al. 2007). Therefore, the interfacial tension and contact angle, under representative storage conditions, are important to fluid flows, phase distributions and capacity of CO2 storage in a reservoir.

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Figure 1 Schematic of the contact angles as observed for a captive bubble

For the determination of reservoir wetting properties, no suitable in-situ measurement exists. Therefore, it is necessary to experimentally determine the wettability in the laboratory, preferably under conditions similar to those in-situ. Of three methods, which are generally accepted for evaluation of the wetting properties of a rock-fluid system (Anderson 1986), the contact angle measurement can be used for a particular surface even at high pressures and elevated temperatures. Based on the value of the contact angle between the three phases, a reservoir rock is considered to be water-wet (θ <75 o_{), intermediate-wet (75}o_{< θ <105} o_{) or oil/gas-wet (θ >105} o_{). Contact angle and}

interfacial tension can be measured in a pendant-drop cell that is modified to analyse the captured bubble at the rock surface. The contact angle method is based on analysing high resolution photographs of droplets/bubbles against the rock surface, which show the contact angle and the shape of vapour-liquid interface.

The main purpose of this study is to examine the wettability behaviour of the Bentheimer sandstone- water system in presence of CO2 and/or flue gas. Direct injection of flue gas into a reservoir or aquifer

could eliminate the necessity of CO2 separation prior to its injection into the reservoir. Hence, this

paper also deals with γwater,CO2 and γwater,flue gas at CO2 storage conditions.

Experimental data for the interfacial tension of pure water and brine against CO2 at reservoir

conditions have been reported by several authors (Chalbaud et al. 2007, Chalbaud et al. 2010, Chalbaud et al. 2009, Chalbaud et al. 2006, Chiquet et al. 2007, Chiquet et al. 2009, Chun and Wilkinson 1995, Georgiadis et al. 2010, Hebach et al. 2002, Kvamme et al. 2007, Nielsen et al. 2012, Shariat et al. 2011, Shariat et al. 2012, Sutjiadi-Sia et al. 2008, Yan et al. 2001). Nonetheless, according to Hebach et. al (2002), there are concerns with the use of these data, with respect to the thermodynamic equilibrium, the image analysis method used, and the lack of accounting for the CO2

dissolution into the water phase and its effect on density. Specially, aside from composition effects (e.g., impurities), IFT measurements are sensitive to density difference between CO2 and the aqueous

phase, thermocouple position within the apparatus, and equilibration time. In the other hand, there are no experimental data available on the interfacial tension of flue gas and water in the literature.

Chalbaud et al. (2007) conducted an extensive set of measurements of interfacial tensions for brine-CO2 systems at different pressure, temperature and salinity conditions representative of CO2 storage

operations. Their results clearly show the necessity of having reliable wettability data to obtain accurate predictions of CO2 sequestration studies (Chalbaud et al. 2010). They also studied wettability

alteration by using 2D glass micro models to track fluid distribution as function of thermodynamic properties and wettability conditions. They concluded that the CO2 does not wet the solid surface for a

strongly hydrophilic porous media, whereas for rock that consists of a significantly smaller amount of hydrophilic minerals the CO2 would significantly wet the surface.

The interfacial interactions between (reservoir) brine, carbonate reservoir rock, and CO2 were studied

in detail by Yang et al. (2005, 2007, 2008) to investigate the effect of temperature and pressure on the wetting properties of wet carbonate systems. They found that the equilibrium contact angle increases

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with increasing pressure and decreases with increasing temperature. These relations may be attributed to higher CO2 solubility in brine at higher pressures and lower temperatures (Yang 2005).

Aguilera and López (2004) examined the behaviour of hydrocarbon-water-CO2 combinations in

cylindrical and square capillaries. Contact angle and interfacial tensions were also measured in an attempt to interpret the results. The authors demonstrated that the decrease in the contact angle and the displacement of the water-hydrocarbon interfaces may be attributed to initial CO2 diffusion through

the water phase and subsequent diffusion throughout the hydrocarbon phase (Aguilera and Ramos 2004).

Effect of chemical treatment on Berea sandstone wettability was investigated by Wu and Firoozabadi (2010). As a result, even small amount of salt ions such as Na+_{can dramatically alter the rock}

wettability from water-wet to intermediate gas-wet (Wu and Firoozabadi 2010).

Espinoza and Santamarina (2010) collect previous results and extended the scope of available data to include saline water, different substrates (amorphous silica, calcite, silica coated with oil, and polytetrafluoroethylene (PTFE)), and a wide pressure range (up to 20 MPa at 298K). They observed contact angles on amorphous silica and calcite substrates remain nearly constant with pressure. Also dissolved NaCl in water increased the contact angle by ~20° for brine on SiO2 and ~4° for brine on

CaCO3 (Espinoza and Santamarina 2010).

The contact angle of CO2 through the brine phase was measured by Mills et al. using the captive

bubble technique (Mills et al. 2011). Their findings show strongly water-wet to water-wet conditions for all the gas and supercritical measurements of CO2 between 800-2000 psi (~ 55 to 138 bar) at 40°C.

Their data shows that the mica and calcite substrates become more water-wet as pressure is reduced, whereas the quartz and biotite substrates become more water-wet by pressurizing the system. A comparison of the measured contact angles for N2 and CO2 shows that the CO2 system is less water

wet than with N2 at low pressure and no clear trend with increasing pressure. They also identified that

supercritical CO2 cannot be characterized by the Amott-USBM method, and concluded that the

contact angle measurement is the most appropriate direct observation of wettability.

Alotaibi et al. (2010) studied oil/water/sandstone interactions at different salinity levels and elevated temperatures by a high-pressure/high-temperature contact-angle method and zeta-potential technique. They found that aquifer water decreased the Berea sandstone wettability toward strongly water-wet (Alotaibi et al. 2010). But, according to their results, different sandstones showed completely opposite behaviour. E.g., for Scioto sandstone, aquifer water enhanced the wettability to intermediate-wet. In addition, there is extensive evidence showing that the salinity and composition of the formation water can alter wetting properties of the reservoir rock (Agbalaka et al. 2009, Dumore 1964, Jerauld et al. 2008, Loahardjo et al. 2010, Piper and Morse 1982, Rezaeidoust et al. 2009, Robertson 2009). Although the wetting properties of mineral surfaces (silica, calcite, biotite and mica) with CO2

injection has been investigated widely in the literature (Chiquet et al. 2007, Espinoza and Santamarina 2010, Mills et al. 2011), but to our knowledge there are only few experimental data available for contact angles on natural rock samples (Alotaibi et al. 2010, Shojai Kaveh et al. 2012, Yang et al. 2007, 2008) and particularly with flue gas injection at high pressures and elevated temperature (Shojai Kaveh et al. 2012). This is due to the complexity of using natural rock for the experimental determination of contact angles; i.e. surface roughness and chemical heterogeneity that are effective on the contact angle value (Shojai Kaveh et al. 2012).

To this end, equilibrium contact-angle and interfacial-tension data are reported here for Bentheimer sandstone and water in presence of CO2 and/or flue gas at a constant temperature of 318 K and

pressures varying between 0.1 and 15 MPa. The experiments were performed such that the aqueous phase was fully saturated with CO2 and/or flue gas, to minimize effects of dissolution and changes in

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2. Exper 2.1. Mat CO2 wit 80 mol% compare other co we choo complic The rock compose approxim porosity consider to the ex the cont taken fr characte which is zero rou factor is descripti were sat 2.2. Exp A modif surfaces Kaveh e capture in Figur allow th Figure 2 The exp (Anton P rimental terials th a purity of % N2 were u ed with com mponents us ose to ignore ating it by re k slab is pre ed of 96% mately of 2% y of Bentheim red to be nat xperiment, o tact angle m om the surfa erization of t s calculated a ughness, Pa is s always high ion on determ turated with w perimental s fied pendant s at varying et al. 2011). and the subs re 2. Both si he visual obse 2 Schematic perimental se Paar K.G. D f 99.7 mol% sed from Lin mbusted air w sually found e these in ord eacting syste epared from quartz (SiO % Kaolinite mer is about turally strong one side of th measurements ace using a the roughnes according to s zero (i.e., th her than zero mination of water in an o set-up and p t drop (PD) c pressures up The determi sequent imag ides of the c ervation of th of experimen et-up consist DMA 512), a and a synthe nde Gas Ben when all oxy

in flue gas, i der to first es ms. a sawed Be O2), a smal homogeneou t 20% and th gly water-we he rock slab s. After the p LEICA 3D s of the surf the internati he Pa value o o. The higher Pa value is g oven at 333 K procedure cell is used t p to 15 MPa ination of th ge analysis. A cell consist o he bubble an ntal set-up (P ts of a high gas compres

etic flue gas nelux. 80/20% ygen was con

i.e. NOx and stablish unde entheimer sa ll fraction usly distribu he permeabi et. The rock

is polished t preparation stereo explo face is based ional standar of a glass sur r the Pa valu given by Sho K for 48 hou to capture C a and a const he contact an A schematic of a steel cap nd substrate i Pendant drop h-pressure br ssor, a gas st consisting o % compositi nverted to C SOx, are rath erstanding of andstone bloc of altered uted througho ility is aroun slab has dim to mitigate th step, 2-D an orer to determ d on the calcu rd of EN ISO rface is about e, the roughe ojai Kaveh e urs. CO2 bubbles u tant elevated ngle is based c drawing of p with glass inside the pen

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feldspars ( out the rock nd 1.5 Darcy mensions of

he effect of s nd 3-D micro mine the sur ulation of th O 4287. For t 0.1 µm). Fo er the surfac et al. (2011). under differe d temperature on visual ob f the experim windows. T ndant drop c

sed after Shoj

t steel cell, o l, circulation of 20 mol% sen because he percentag mpared to N2 a ility behavior ntheimer san (less than 2 matrix. The y. The Benth 30×6×12 mm surface roug oscopic ima rface roughn he so-called P an ideal surf or real surfac ce is. A more . Then the ro ent natural s re of 318 K bservation i. mental set-up These glass cell. ojai et al. 201 online densi n pump, two CO2 and it can be es of the and CO2, r without dstone is 2%) and e average heimer is m3_{. Prior} ghness on ges were ness. The Pa factor, face with ces the Pa e detailed ock slabs sandstone ) (Shojai .e. image p is given windows 12) ity meter pressure

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gauges with an accuracy of 0.01 bar, two temperature gauges with the accuracy of 0.1 K, a high-resolution digital camera and an endoscope. The maximum pressure of the cell is 600 bar and of the lines 180 bar. Before an experimental run the substrate is placed inside the cell. Then the cell is closed and tested for leaks: specifically, the cell is pressurized with helium up to a pressure of 180 bar. Prior to use all lines and the cell itself are rinsed with ethanol and distilled water to remove possible impurities introduced during the mounting of the cell. After removal of leakages, the cell is filled with distilled water. The cell is filled such that the liquid level of the water in the cell is higher than the lower end of the substrate. Before CO2 or flue gas can be added to the cell, it is pressurized in a

separate cell by means of a compressor. The carbon dioxide and/or flue gas is injected into the cell from this storage vessel. Gas of the pressurized vessel is then injected into the main cell. Once enough gas is injected, circulation starts to ensure mixing of the gas and water and to attain equilibrium. In this work, both interfacial tension and contact angle measurements were conducted with water fully saturated with CO2 or flue gas to eliminate the effect of any change in the composition of the aqueous

phase and to minimize dissolution effects. For the CO2 system the overall composition of the mixture

can be determined using the equation of state for CO2 provided by Span and Wagner (1996), as well

as through a simple material balance. Phase equilibrium data for the CO2–water system by Shyu et al.

(Shyu et al. 1997) are used to ensure that the overall composition is such that the experiments are conducted in a fully-saturated aqueous phase. Equilibrium was judged to be achieved when the pressure in the cell stayed constant and the density of the re-circulating liquid did not change anymore.

To conduct experiments to determine the contact-angle and interfacial-tension after establishing a saturated aqueous phase at the desired pressure, a small amount of gas was added to the cell via the small needle-lie inlet at the bottom of the cell. In order to avoid erroneous results due to reflection and imaging artefacts, the light beam, the substrate, the endoscope and the camera need to be aligned. If the liquid phase was completely saturated with gas, the bubble remains stable. Images of the bubble were taken and then used as input for the image-analysis step to determine the interfacial tension and contact angle. Images are analysed using the Drop Shape Analysis (DSA4) KRUESS©_{software giving}

the contact angle and interfacial tension values based on the ADSA technique (Song and Springer 1996). After taking pictures at a certain pressure, the pressure inside the cell is increased by adding more gas to the cell. A detailed description of the experimental setup and procedure can be found in previous work (Shojai Kaveh et al. 2011).

3. Results and Discussions

3.1. Interfacial tension measurements: The CO2/H2O and flue gas/H2O systems

Common experimental techniques for determining CO2–water/ brine interfacial tension (IFT) include

the pendant-drop method, the capillary-rise technique and the sessile-drop method. In the pendant drop method, a small bubble of gas phase (CO2 or flue gas) is injected from a needle-lie inlet into the

gas-saturated aqueous phase (water or brine) kept at the desired pressure and temperature. The droplet shape is recorded and analysed to determine IFT. The determination of interfacial tensions requires that the density difference between CO2 or flue gas and the aqueous phase (Δρ) is known. The

experimental CO2–water IFT values vary widely in the literature, particularly those determined close

to the critical point of CO2. Due to the sensitivity of the experimental IFT measurement to the

thermocouple position and the previously mentioned issues, such as ageing time etc., reported experimental data are scattered and occasionally contradictory. Therefore, reports which do not indicate the position of the thermocouple and/or do not report the temperature near the CO2–water

interface should be excluded from a data set when used for comparison. To help validating our IFT data, we made a comparison of our measurements with the published results of Chiquet et al. (2007), Chun and Wilkinson (1995), and Kvamme et al. (2007). In Figure 3, the pressure dependency of the

measured CO2-distilled water IFT is depicted. The experiments were conducted at a constant

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temperat (2007), t pressure reported Figure values b Chiquet In gener bar. Thi range, it (Baranen (Figure 4 Figure 4 CO2 at a relative ture in our the IFT valu e range inves d in Chiqeut e 3 Comparis by Chun et a et al. (2007) ral, IFT of th is trend is re t can be see nko et al. 1 4). 4 Dimension a constant te values divid experiments ues of this stu

stigated. In et al. (2009). son of CO2 -al. (1995), C ) data is repo he CO2/wate elated to the en that the d 990) strongl nless density emperature 3 ded by the res

s. Except for udy are in go addition, for . water IFT e Chiquet et al orted in Chiq er system de solubility of density (Span ly increase b (Span and W 18 K and pr spective max r the experi ood agreeme r the Chique experimental l. (2007) and qeut et al. (2 ecreases with f CO2 in wat n and Wagn before they Wagner, 199 ressure range ximum value mental IFT ent with thos et et al. (200 lly determin d Kvamme e 009). h increasing ter and CO2 ner 1996) an become alm 96) and solub e from atmos in the pressu determinatio se reported in 07) measurem ned in this s et al. (2007). pressure at density (Fig d the solubi most constant bility (Baran spheric up to ure range. on by Chiqu in the literatu ments, uncer study with p . Uncertainty pressures be g. 4). In this ility of CO2 t at higher p nenko et al., o 20 MPa. Va uet et al. ure at the rtainty is published ty for the elow 100 pressure in water pressures 1990) of alues are

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Figure 5 temperat et al. (20 Figure 5 systems. Due to t water is and solu density of N2 so increasin density a Figure 6 5 shows the I ture of 318 K 001). 5 Compariso

the high perc closer to th ubility in wa increase wit olubility and ng pressure. and solubilit 6 Interfacial IOR 2013 – 1 IFT data of s K. The IFT on of experim centage of N at of N2 than ater on the IF th pressure c d density w Since the d ty of nitrogen tension and 17th European St. Petersburg synthetic flue value of nitr mentally dete N2 (80 mol%) n to that of C FT values, r correlates wi ith pressure density and s n, the IFT va density rela n Symposium g, Russia, 16-e gas-wat16-er, rogen/distille ermined IFTs ) in flue gas, CO2. Figure respectively. ith a decreas , IFT of the solubility of alue of the flu

tion for flue

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Both the so e in CO2/wa

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Figure systems. This pre visible f bubble h Figure phase at gas- satu 7 Interfacia essure depen from the ima has no recogn 8 Digital im t 318 K: (a) P urated water al tension an ndency of in ages in Figu nizable chan mages of CO P=5.5 bar a r as liquid ph nd solubility nterfacial ten re 8. Unlike nge from

sub-O2 pendant d nd (b) P=15 hase at 318 K y relation fo nsion for CO e the CO2 bu -critical (Fig drop in the 51.1 bar, and K: (c) P=13. or flue gas-w O2 and flue g ubble (Fig. 8 g.8(c)) to sup presence of d flue gas pen

15 bar and ( water, CO2 -gas/water sy (a, b)), the s er-critical (F f CO2- satur ndant drop in (d) P=149.24 -water and N ystems is als shape of the Fig.8(d)) pres rated water n the presenc 4 bar. N2-water o clearly flue gas ssure. as liquid ce of flue

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3.2. Con 3.2.1. Be Releasin size and associate provides dissoluti which h discusse propertie angle sh composi In the b values h aqueous which h 2007, 20 angle af function al. (200 imbibitio imbibitio The stab Figure 9 at high p the stabl Figure 9 ntact angle m entheimer s ng the CO2 b d accordingly ed to the dis s important i ion, diffusio has been obse

ed mechanis es of the su hould be de ition and min beginning of

have an initi s phase. Afte as been char 008). In this fter the injec n of time was 07), the volu on of CO2 i on is unlikel ble contact a 9 as a functio pressures. Ho le contact an 9 Stable cont IOR 2013 – 1 measuremen andstone/w bubble in a n y of contact ssolution of information c on, and conv erved during ms and par rface. There etermined in nimize disso f gas bubble ial fluctuatio er short agin racterized as s study the a ction of the s presented in ume reductio into the roc y. angles of the on of pressur owever, the ngle as functi tact angles a 17th European St. Petersburg nts ater/CO2 sy non-equilibr angle with t CO2 into th concerning th vective mass g the dynami ameter chan efore, to stud n a fully sat lution effects injection int on due to th ng time, the c the ‘stable c aging time is gas bubble. n our previou on of the bu k; in their c CO2/sandsto re. It shows t scatter in the on of pressu as a function n Symposium g, Russia, 16-ystem rated aqueou time. This is he water pha he dynamic p s transfer. A ic contact an nges, and by dy the wettin aturated syst s.

nto the equili e mutual ma contact angl contact angle s defined as The variatio us work (Sho ubble is due case a carbo one/water sy that sandston e contact ang ure. of pressure on Improved 18 April 2013 us phase caus s called the ‘ ase. Investiga phenomena t Accordingly, ngle investiga y that not s ng propertie em to elimi ibrated wate ass transfer le reaches to e’ (Shojai Ka the time ne on of the co ojai Kaveh e e to mass tr onate. In ou ystem at a te ne/water/CO gle is very la at 318 K for Oil Recovery 3 ses a fast de dynamic con ation on dyn that occur at , apparent w ation, is rela olely depen s of the surf inate the ef r–CO2 syste between the a constant v aveh et al. 20 cessary to re ntact angle a et al. 2012). A ransfer as d ur case with emperature o 2 system rem

arge and ther

CO2-water-s y ecrease of th ntact angle’ namic contac t the interfac wettability a ated to the pr ndent on the face, reliable ffect of alter em, the conta e gas bubble value at equ 011, 2012, Y each a stable and bubble According to described ab mostly qua of 318 K are mains water-re is no clear sandstone sy he bubble which is ct angles e such as alteration, reviously e wetting e contact ration in act angle e and the uilibrium, ang et al. e contact size as a o Yang et ove, and artz, CO2 given in wet even r trend of ystem.

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The stab contact the cont experim roughne mineral contact-and calc Figure 1 system. Figure different K. The c contact relativel The con surface imply th prepara proper depende stable c changes publish Espinoz was rep ble contact angle on th tact angle d mental resul ess. The ov logy (Vijapu -angle mea cite surface 10 Stable co 11 compare t sub- and su comparison angles have ly unchanged ntact angle heterogene hat bubble ation and th measure th ency of con contact angl s. Our find ed data for za study a s ported. angles as a he bubble r decreases as lts in Figur verall effec urapu 2002 surement o s. ontact angle s the measu uper-critical of different no recogniz d, within the variation w eity (Drelich size depend he extent to hat quantifie ntact angles le is more i dings comp r a smooth mooth quar a function of radius for a s the bubble re 9 is rela ct of rough 2). Vijapura n silica-bas s as a funct ured stable pressures as pressures (c zable change ranges of the with bubble h 1997, Dre dency of co o which the es the relati s is currentl nfluenced b are very fa quartz pla rtz plate wa f bubble rad a CO2-water e radius incr ated to the hness on th apu found th sed surfaces tion of bubb contact ang s function of olours), with e from sub-c e error bars. e size is af elich et al. ontact angle e CO2 may ion betwee ly lacking. O by the bubb avourably w ate (Espinoz as used, no d dius (Figure r-sandstone reases. It ap bubble siz e contact a hat the effec

s is more c le radius at les of the C f bubble size h a comparab critical to su ffected main 1996, Good es is related y penetrate n surface r Our experim ble size (and with the tre za and San dependency e 10) shows system. Fig ppears that t ze that caus angle is rel ct of surfac onsiderable 318 K for C CO2-water- at a constan ble CO2 bub uper-critical nly by surf d and Koo 1 to the qual in the sub oughness a mental resul d roughness end establis ntamarina 2 y of contact s the depend gure 10 sho the scatterin sed by the lated to the ce roughnes e than the d CO2-water-s sandstone s nt temperatur bble size, rev pressure and

face roughn 1979). Tha lity of the s bstrate. How and the bub ults confirm s) than the p shed by pre 2010). Sinc angle to the dency of ows that ng of the surface e matrix ss on the dolomite andstone ystem at re of 318 veals that d remain ness and at would substrate wever, a bble size that the pressure eviously e in the e bubble

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Figure Bentheim constant To min contact (Figure bubble Figure 1 sandston green li height of 3.2.2. Be The stab Figures bubbles of 20 m significa 11 Compari mer sandsto t temperature imize depen angle dete 12). This size. 12 (a) 3-D sa ne sample su ines give the f primary pr entheimer s

ble contact an 13-15 as a are all smal mol% CO2 t antly lower t IOR 2013 – 1 ison of the e ne system a e of 318 K. ndency on s rmination a degree of ample surfac urface. The p e orthogonal rofiles, i.e. th andstone/w ngles of flue function of ler than thos o 80 mol% than that of 17th European St. Petersburg experimenta at sub- and s surface qual at a resoluti smoothnes ce with a view pictures are t l x, y, z dire e factor Pa. F ater/synthet e gas/Benthei pressure and se of the CO N2 in the f CO2. As a r n Symposium g, Russia, 16-lly determin super-critica lity, in this ion of 0.1 m ss still may w width of 4 taken with a ections used For this subs tic flue gas s

imer/water s d flue gas b O2 bubbles (F

flue gas bub result, the co on Improved 18 April 2013 ned stable co al pressures work we pr mm as show y cause var 4 mm; (b) per LEICA 3D s d for the dete

strate Pa= 0. system system at a te bubble radius Figure 13). T bble. The so ontribution o Oil Recovery 3 ontact angle as function repared smo wn in the m riation of c rpendicular v stereo explor ermination o 03 mm. emperature o s. Contact an This can be e olubility of f nitrogen to y es of the CO n of bubble s ooth surface microscopic contact angl view of a Be rer. The blue of the mean of 318 K are ngles of the explained by nitrogen in o the variatio O2 -water-size at a e for the c images les with entheimer , red and average e given in flue gas the ratio water is on of the

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contact addition size (thu with bub system, pressure Figure system. Figure 1 system. angle is sm n, in the flue us surface ro

bble size for i.e. contact e changes (Fi

13 Stable c

14 Stable co

mall and the gas-sandsto oughness) th r a compara angles rema igure 15). ontact angle ontact angle trend of th one-water sy han by the p able flue gas in relatively

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as a function

he contact an stem the con pressure chan s bubble size y unchanged, tion of press n of bubble r ngle is dom ntact angle i nge (Figure e shows a s within the r sure at 318 radius at 31 minated by th s more influ 14). The tre imilar trend ranges of the K for flue 8 K for flue he CO2 beh uenced by th end of conta d as found fo e error bars, gas-water-s gas-water-s avior. In he bubble ct angles or a CO2 with the andstone andstone

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Figure Bentheim constant 4. Conc In this w for a wi angles o tension gas to e the disso  Th  Th  Th  A  Th 15 Compari mer sandsto t temperature lusions work, interfa de range of of water/Bent and contact liminate the olution effec he CO2-wate occurs in th decreases at he flue gas-w is similar to changes with he contact a remains) wa All contact an he contact an size in the pr IOR 2013 – 1 ison of the e ne system a e of 318 K. acial tension pressures at theimer sand angle measu effect of an t. The results er interfacial e lower pres a very slow water IFT de o the one of h pressure. angle measu ater-wet even ngles of the fl ngle of the w resence of su 17th European St. Petersburg experimental at sub- and s of water/CO a constant t dstone system urements wer ny changes in s are summa tension decr ssure range u rate. ecreases sligh the nitrogen urements sho n at high pres lue gas bubb water–sandst urface roughn n Symposium g, Russia, 16-lly determine super-critica O2 and/or syn temperature o m were determ re conducted n the compo arized as follo reases with i up to 100 ba htly for all p n/water syste ow that the ssures with C bles are small tone system hness with eit

on Improved 18 April 2013 ed stable c al pressures nthetic flue g of 318K. In mined with C d with water osition of the ows: increasing pr ar. At higher pressure rang em and is att Bentheimer CO2 and/or fl

ler than those demonstrate ther CO2 or f Oil Recovery 3 ontact angle as function gas is experi addition, the CO2 and flue r fully satura e aqueous ph ressure. The pressures, th ges. The IFT

tributed to s sandstone/w lue gas. e of the CO2 s a strong de flue gas. y es of flue ga n of bubble s imentally de e equilibrium e gas. Both in ated with CO hase and to m e considerabl he interfacia trend for thi solubility and water system 2 bubbles. ependency o as-water-size at a etermined m contact nterfacial O2 or flue minimize le change al tension is system d density m is (and on bubble

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Acknowledgements

The research reported in this paper is carried out as a part of the CATO2 project (CO2 capture,

transport and storage in the Netherlands). This research is conducted in the Laboratory of Geoscience and Engineering at Delft University of Technology. Our grateful thanks to the technical staff of the Laboratory, particulary J. Etienne, M. Friebel, K. Heller and J. van Meel.

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