Foam Performance in Low Permeability Laminated Sandstones

Foam Performance in Low Permeability Laminated SandstonesJonas S. Solbakken,*,†,‡ Arne Skauge,†,‡ and Morten Gunnar Aarra†

†Centre for Integrated Petroleum Research, ‡Uni Research, University of Bergen, Allegaten 41, N-5020 Bergen, Norway

ABSTRACT: Most studies on foam are related to homogeneous and highly permeable porous media. As the reservoir situationis rather heterogeneous with respect to permeability and layering, foam properties in layered porous media with lowerpermeabilities are also important to understand. This study investigates foam behavior and performance in naturally laminatedsandstone cores. Laminations are common constituents in sandstone petroleum reservoirs where they usually occur as thindeformed layers in the host formation. Evidences of rock heterogeneity were confirmed by several different analyses on laminatedmaterial. From image processing of thin sections and 2D X-ray experiments, the laminas present were found to exhibit both lowerporosity and permeability than the host rock, and also shown to form barriers to fluid flow. Foam experiments were performed inthree low permeability sandstone cores with relative similar permeability but with a different degree of laminated stratificationsparallel to flow direction. Foam was generated in all the low permeability laminated cores. However, the degree of lamina in eachcore influenced foam performance significantly, reflected by large variations in mobility reduction factors (MRF ∼ 20−500) andfoam breakthrough times. Increased lamination resulted in weaker foams and earlier foam breakthroughs. One explanation to thiscould be that the low permeability laminas introduce different degrees of discontinuities and compartmentalization to foam flow.Findings in our study indicate that foam properties and performance can be strongly influenced by local heterogeneities, such aslaminations naturally found in many sandstone reservoirs.

2. INTRODUCTION

The low gas viscosity relative to water and oil makes the gasvery mobile in porous media. A critical factor of a regular gasinjection related to oil recovery is therefore early gasbreakthrough and, consequently, poor sweep efficiency. Foamcan be applied to control gas mobility in porous media. Whengas is dispersed in a liquid, the gas phase becomesdiscontinuous and less mobile by continuous liquid films. Asurfactant is normally used to stabilize the gas−liquid surface.Injection of foam can block and divert fluid flow, which mayimprove the sweep efficiency. Several successful foam fieldprojects have been accomplished. The generated foams haveshown stability and robustness to tough test conditions and assuch qualified foam as an enhanced oil recovery (EOR)method.1−4

2.1. Foam in Low Permeability Porous Media. Theearliest studies on foam identified and emphasized theefficiency of foam to reduce gas mobility in high permeableand homogeneous sand packs.5−7 Experimentally, Lee andHeller8 and Mannhardt and Novosad9 both found the foamstrength, defined through the mobility reduction factor (MRF),to decrease with lowering core permeability. Some authors havespeculated if a threshold in permeability to foam may exist,often discussed in relation to the limiting capillary pressuretheory, where the capillary pressure is thought to control foamproperties. The stability of foam in porous media depends onhow the limiting capillary pressure varies with permeability,which also is reported to depend on surfactant type andconcentration, salinity, rock type, foam quality and gas/waterflow rates used.10−13 Nevertheless, several studies havegenerated strong foams in relative low permeability porousmedia and, thus, questioned if a threshold in permeability tofoam really exist.14−17

2.2. Foam in Heterogeneous Porous Media. Perme-ability contrasts within the porous media may lead to furtherintensifying in instabilities of the gas injection front, such as gaschanneling and excessive flow through the most permeableregions. Foam has been recognized as a promising method forcontrolling gas mobility in heterogeneous porous media. Afavorable property of foam is that foam generation will occur inthe most permeable zones first, diverting flow to the lesspermeable zones. This property has been confirmed by severalresearchers when two cores with contrasting permeabilitieswere arranged in parallel with no capillary communication.18−24

Siddiqui et al.23 found that the permeability difference betweentwo cores played the most important role in foam diversion andthat the chances of getting diversion improved when thepermeability contrast increased. This result was contradictorycompared to earlier findings.24 Others have investigated foamflow performance in heterogeneous systems where capillarycontact and flow among layers were allowed, denoted as cross-flow.13,25,26 Selective mobility reduction (SMR) and self-regulating foam behaviors have been reported when cross-flow was possible.25,26 An ideal SMR or self-regulating behaviorimplies that the foam displacement front will propagate at equalvelocity in each layer, independent of permeability. Bertin andco-workers26 confirmed this effect on a heterogeneous poroussystem made of consolidated sandstone surrounded withunconsolidated sand in the annular region. Gas breakthroughclose to one pore volume injected was used as a measure toindicate how favorable fluid mobility in heterogeneous porousmedia could be when foam was applied.

Received: August 13, 2013Revised: January 19, 2014Published: January 23, 2014

Article

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© 2014 American Chemical Society 803 dx.doi.org/10.1021/ef402020x | Energy Fuels 2014, 28, 803−815

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This study investigates foam behavior and performance innaturally laminated sandstone core material with lowerpermeability than normally studied. The literature on foam innaturally layered systems is limited. One major challenge withsuch complex systems is obviously to detect and quantify theheterogeneity. A suite of techniques were therefore used toanalyze and better characterize the laminated rock materialprior to experimental foam studies.Foam was generated by coinjection of surfactant solution

(AOS C14−C16) and N2-gas at elevated experimentalconditions. The laboratory results presented show significantdifferent foam behavior and performance in three heteroge-neous cores with relative similar permeability. This might havegreat implications for realistic and accurate simulation andscaling of foam flooding processes. The detection of coreheterogeneity through various rock analyses seems importanttoward improved understanding of foam results in heteroge-neous reservoir core material.

3. EXPERIMENTAL SECTION3.1. Core Material. Physical properties of the outcrop Berea

sandstone core material used in this study are given in Table 1. Thecores were named after degree of lamina present in each core: Weaklylaminated (B-WL), moderately laminated (B-ML), and stronglylaminated (B-SL).

Cores were cut and dried in an oven at 70 °C for 24 h. The dry corewas surrounded by a Teflon sleeve, wrapped by aluminum foil andthen covered with a Viton rubber sleeve before mounted into a coreholder. The core was vacuumed and saturated 100% with syntheticseawater (SSW) and absolute permeability to water (Kw) wasmeasured.3.2. Brine. The composition of the seawater used in this study is

listed in Table 2.

3.3. Gas. Industrial grade nitrogen delivered by Yara Internationalwas used as gas phase in this study.3.4. Surfactant. An anionic alpha olefin sulfonate surfactant, AOS

C14−C16 was used in this study. The surfactant concentration was 0.5wt % in all experiments. The AOS surfactant was delivered as liquid of37.6% active material with a molecular weight of 324 g/mol. Thechoice of foamer is based on promising results from earlier work andfield studies using AOS surfactants. The surfactant is commercial andavailable at low price. The surfactant solution in this study wasprepared by mixing surfactant with brine (SSW).3.5. Experimental Procedures. The experimental setup used for

high pressure and high temperature (HPHT) N2-foam experiments inthis study is shown in Figure 1. In all foam experiments, we used thecoinjection method, injecting surfactant solution and N2 from separatereservoirs into porous media. Total injection rate was set to 40 ml/h(i.e., 32 mL/h with N2 and 8 mL/h with surfactant solution). The total

injection rate corresponds to a superficial velocity of 0.9 m/day. Foamquality (i.e., fraction of gas) was always 0.80 ± 0.01 at the inlet end ofthe core. Two HPHT Quizix pumps located inside the heat cabinetwere used to control the injection rates. The pumps are able to becontinually refilled at the inlet pressure of the core. This ensuresconstant inflow foam quality throughout the entire experiment.Confining pressure was kept 45 ± 5 bar over the injection pressure(P1) at all times. Behind the core outlet, a sight-glass was mounted onthe line. Through the sight-glass, with inner diameter of 1.5 mm, wewere able to observe foam at experimental conditions out from thecore. The sight glass was used to confirm foam generation and todetermine foam breakthrough times. Fluids that were produced fromthe core were either collected into production cylinders or producedthrough a back pressure regulator (BPR) at constant outlet pressure(P2). Production cylinders can be advantageous to use to provideacquisition of pressure data with minimum noise or oscillation oftenassociated with the back pressure regulator. A heat cabinet supportedthe experimental setup with constant elevated temperature (±1 °C).

Several experiments were performed in the same core. Before thenext experiment was started, the core was usually depressurized andthen flooded with large volumes of brine (3 wt % NaCl) and isopropylalcohol (a good gas dissolver) to make the core 100% water saturatedagain. Restored core permeability or permeability as close as possibleto the absolute permeability was used as criteria before starting a newset of experiment. Between 85 and 100% of the original permeabilitywas usually restored. Good experimental reproducibility in subsequentexperiment with this procedure was obtained in our recent work.27

3.6. Experimental Summary. The following steps include in eachfoam core flooding experiment at HPHT:

(1) Baseline experiment: simultaneous injection of N2-gas and SSWat 80% gas fraction (Qtot = 40 mL/h).

(2) Injection of two pore volumes of surfactant prior to foamgeneration (Q = 8 mL/h).

(3) Foam generation: simultaneous injection of N2-gas andsurfactant solution at 80% foam quality.

(4) Cleaning of the core back to absolute water permeability (Kw).

The generated foams were characterized by several parameters suchas pressure build-up along the core, mobility reduction factors (MRF),and visual observation of foam breakthrough from the sight-glassmounted at core outlet. Calculation of MRF is a method to determineand to compare the strength of the foams generated. MRF is definedas the ratio of the pressure drop in the presence of foam (during foamgeneration) to the corresponding pressure drop in the absence of foam(during baseline experiment) using the same flow rates and volumefractions (see eq 1).28 For baseline pressure, we always used theaverage value of the steady state pressure drop for the last 0.5 pore

Table 1. Physical Properties of the Core Material

core IDlength[cm]

diam.[cm]

crosssection

area [cm2]

porevol.[mL]

avg.porosity[%]

avg.permeability,Kw [mD]

B-WL 29.9 3.75 11.04 57.0 17.3 66.9B-ML 30.0 3.76 11.10 58.5 17.6 93.1B-SL 23.5 3.76 11.10 49.3 18.9 130.0

Table 2. Synthetic Seawater (SSW) Compositiona

salt NaCl Na2SO4 NaHCO3 KCl MgCl2 CaCl2[wt %] 2.489 0.406 0.019 0.068 0.521 0.131

aThe SSW was filtered through a 0.45 μm filter before use.

Figure 1. Experimental setup for high pressure and high temperaturefoam experiments: dP = differential pressure, P1 = injection pressure,P2 = production pressure, GP = gas pump (Quizix), SP = surfactantpump (Quizix), BPR = backpressure regulator.

Energy & Fuels Article

dx.doi.org/10.1021/ef402020x | Energy Fuels 2014, 28, 803−815804

volume of gas and brine injected. All the baseline pressures obtainedand used for calculation of MRF in each experiment (i.e., dPwithout foam)are tabulated in Table 3.

=

=

+

+Mobility reduction factor (MRF)

dP

dP

dP

dP

(gas surfactant)

(gas water)

(with foam)

(without foam) (1)

4. RESULTSCORE ANALYSES ON LAMINATED ROCKMATERIAL

The different core analyses applied on used rock material in thisstudy are presented in Appendix A. Results from these analyseshave been used as a supplement in our interpretation anddiscussion of the main foam flooding experiments at elevatedconditions.Both visual observation and X-ray imaging showed that

different degree of laminations parallel to flow direction waspresent in each core (Figure A.5 in Appendix A). Also, thinsection analyses from the inlet end of the cores confirmedvarying degree of lamina to be present. The laminas were seento be through-going in all the cores with various thicknessesand densities along. Dispersion tests (water displacement intoinitially water saturated core) indicated early tracer break-through and tailing of the dispersion profiles in the laminatedcores (Figure A.6). Interestingly, the dispersion profile did notreflect any particular difference between the weakly and themoderately laminated core (B-WL and B-ML). The mostanomalous dispersion profile was seen for the stronglylaminated core (B-SL). Some of the rock heterogeneity presentin B-SL was observed as clusters of cementation rather thanthin layers of single structures (Figure A.4c). Back scatterelectron microscopy (BSE) images were used to estimatepermeability and porosity within several laminas using themethodology described by Torabi et al.29 In general, lowerpermeabilities and porosities were found in the laminascompared to host rock. 2D X-ray scanning was also utilizedto obtain more information about foam and fluid flow inlaminated rock material. The laminated sandstone slabs used inthese experiments illustrated relative high degree of lamina tobe present (Figure A.8). Flooding experiments at low pressure(2 bar and 25 °C) demonstrated that the laminas could act asbarriers to both foam and fluid flow (Figures A.9 and A.10).Visual observation showed that foam was able to reduce gas

mobility and improve gas sweep efficiency in laminated corematerial compared to regular gas injection without surfactant(Figure A.10).

5. MAIN RESULTSFOAM FLOODING IN LAMINATEDROCK MATERIAL

Foam flooding experiments were performed in three laminatedBerea sandstone cores with low permeability. The corescontained different degree of laminations parallel to flowdirection (B-WL, B-ML and B-SL). Foam was generated bycoinjection of surfactant solution (AOS C14−C16) and N2-gasat pressures of 30, 120, and 280 bar and 50 °C. 80% foamquality (fraction of gas) was used in all experiments.

5.1. Foam Generation in B-WL (Weakly LaminatedCore). Results from N2-foam generation in B-WL at 120 barand 50 °C are shown in Figure 2.

Figure 2 describes the MRFs and differential pressuresobtained in B-WL during N2-foam generation. Very strong N2-foams were generated in this weakly laminated sandstone core(MRF close to 500). Foam breakthrough was observed in thesight-glass close to one pore volume injected. This was aconsiderable improvement compared to gas breakthroughduring baseline experiment (that is only injecting N2-gas andseawater), which was observed after less than 0.2 pore volumeinjected. With foam present in the core, gas propagated close tothe injection rate in B-WL. Good reproducibility of foamexperiment 1 was found both with respect to foam propagationand foam strength (expt. 2 in Figure 2).Even though laminations were present in B-WL, the results

indicated that foam was able to effectively control gas mobilityin the low permeability laminated sandstone core flooded. Theresponses obtained in B-WL with effective pressure build-up,significant delayed foam breakthrough and good experimentalreproducibility in subsequent foam experiment are similar toour N2-foams generated in recent work in a homogeneous andhigh permeability Berea sandstone core.27

5.2. Foam Generation in B-ML (Moderately LaminatedCore). Results from foam generation in B-ML are shown inFigure 3. Effect of pressure (30, 120, and 280 bar) wassystematically tested at 50 °C with respect to foam properties inlaminated core material. Foam breakthrough times observed inthe sight-glass at core outlet in each experiment are given inFigure 4.Strong N2-foams were generated in all foam experiments at

all the different system pressures applied. The foam strength inB-ML was not negatively affected by increased system pressure(30−280 bar). In fact, slightly improved foam strength withpressure was observed. Similar result on the effect of pressure

Table 3. Baseline Pressures

core IDexpt. no.

(in same core) conditions (P, T)dPwithout foam(mbar)

B-WL 1 120 bar, 50 °C 270B-WL 2 120 bar, 50 °C 273

B-ML 1 30 bar, 50 °C 217B-ML 2 120 bar, 50 °C 227B-ML 3 280 bar, 50 °C 228B-ML 4 280 bar, 100 °C 177B-ML 5 280 bar, 50 °C

(Qtot = 8 mL/h)178

B-ML 6 30 bar, 50 °C 250B-ML 7 120 bar, 50 °C 257

B-SL 1 30 bar, 50 °C 165B-SL 2 30 bar, 50 °C 165

Figure 2.Mobility reduction factors and differential pressures obtainedin B-WL during foam generation at 120 bar and 50 °C.



on N2-foam strength was also obtained in our recent work inhomogeneous and high permeable Berea sandstone.27 Foamgeneration at high pressure and high temperature conditionsusing AOS surfactant have also been reported by severalothers.14,30−35

Interesting responses in B-ML compared to B-WL were seen,attended with (I) no plateau in differential pressure, even aftermore than five pore volumes of fluids injected; (II) largedifferences in MRF compared to B-WL; (III) earlier foambreakthroughs than expected for all three foam experiments(0.44−0.58 PV).The consistent early foam breakthroughs observed for all

three experiments indicate that the effectiveness of foam tocontrol gas mobility in B-ML was reduced compared to B-WL.Even though the physical properties of the cores listed in

Table 1 illustrate that B-WL and B-ML appear as relativelysimilar (with respect to Kw, porosity, pore volume, core length),large differences in MRF (∼100−500) were obtained in thesetwo cores. One immediate explanation to the different foamperformances experienced between B-ML and B-WL could bethe different degree of lamination that is present in each core. Ahigher degree of low permeability laminas in B-ML versus B-WL may have reduced the efficiency of foam to control gasmobility. Reduced mobility control in B-ML was reflected byweaker N2-foams, earlier foam breakthroughs, and less effectivepressure build-ups.5.3. N2-Foam Generation in B-SL (Strongly Laminated

Core). In the literature, foam generation and foam propagationproperties have been discussed with respect to surfactantadsorption.15 Bai et al.36 tested surfactant adsorption of ananionic surfactant in Berea sandstone (224 mD) and showedthat it took about a week to reach the final equilibrium in

adsorption. They discussed this to areas of slow contact, due tomicropores, secondary porosity, and dead-end pores found inthe complex structures of the Berea sandstone used. In ourstudy, we always injected two pore volumes of surfactant priorto each foam generation. Is this enough to cover surfactantadsorption in low permeability laminated rocks?Our interest in the next core flooded, B-SL (strongly

laminated), was therefore to investigate if volume of surfactantsolution injected prior to foam generation in laminated corematerial would have any effect on foam performance.A new low permeability laminated sandstone core, B-SL, was

used to test and to compare the effect of 2 versus 20 porevolumes of surfactant solution injected prior to foamgeneration. Both experiments were performed at 30 bar and50 °C. Results from foam generation in B-SL are given inFigure 5.

Again, N2-foams were generated, even in strongly laminatedsandstone core material. The generated foams in B-SL were,however, the weakest ones compared to those obtained in B-WL and B-ML, reflected by the lowest MRFs. A somewhatfaster increase in pressure build-up was observed when 20instead of 2 pore volumes of surfactant solution had beeninjected prior to foam generation (expt. 2 in Figure 5). As thegeneration continued, more than 2 pore volumes of surfactantsolution injected indicated to only have a minor effect on theoverall foam strength obtained (although a doubling in MRF).Foam breakthrough occurred early in the sight glass for bothexperiments (∼0.4 PV). Again, the properties of the stronglylaminated core material seems to be a more important factoraffecting foam performance than number of pore volumesurfactant injected.

5.4. Summary. Figure 6 compares and summarizes theMRFs obtained in this study with respect to core material andsubsequent experiment in each core. Figure 7 compares averagebreakthrough times observed in the sight glass at core outlet.

5.5. Reproducibility in Laminated Core Material. Inaddition to the three foam generations conducted in B-ML(Figure 3), four new foam experiments were performed in thiscore. The interest was to evaluate if foam properties could besystematically studied and reproduced in laminated rockmaterial. Restored core permeability or permeability as closeas possible to the absolute permeability was used as a criterionbefore a new foam experiment was started. Good reproduci-bility in subsequent experiment with this procedure was foundin our recent work in homogeneous and high permeable Bereasandstone, even after 11 experiments in the same core.27

Figure 3. Mobility reduction factors obtained in B-ML during foamgeneration at different experimental conditions.

Figure 4. Comparison of foam breakthrough times observed in B-MLat different experimental conditions.

Figure 5. Mobility reduction factors obtained in B-SL with differentamount of surfactant injected. (Both experiments performed at 30 barand 50 °C.)



Figure 8 shows the reproducibility experiments performed inB-ML with respect to system pressure (i.e., 30 and 120 bar at

50 °C, respectively). Poor experimental reproducibility in B-ML was observed with respect to absolute pressure. Figure 9compares and summarizes the MRFs obtained in all seven foamexperiments conducted in B-ML. Different variables such aspressure (30, 120, and 280 bar), temperature (50 and 100 °C),and injection rate (40 vs 8 mL/h) were systematically testedwith respect to foam properties in B-WL.

Results from both Figure 8 and Figure 9 illustrate thatsuccessive stronger foams seems to be generated for repeatedexperiments in B-ML, independent of the variables tested. Apossible explanation to this observation is discussed later (see6.2).Consistent early foam breakthroughs were observed in the

sight glass for all seven experiments performed in B-ML (earlierthan 0.6 pore volume injected). The poor reproducibilitywitnessed is an additional proof of the studied foam propertiesand performances being controlled by the laminated corematerial.

6. DISCUSSIONThe main findings from this study have shown that in situ N2-foams were able to generate within all three low permeabilitylaminated sandstone cores flooded using AOS surfactant. Foamgeneration was observed at high pressures (30, 120, and 280bar) and elevated temperatures (50 and 100 °C). The positiveresponse for the AOS surfactant at high pressure andtemperature conditions may be attractive to potential foamfield applications.Main findings in this study also demonstrated that the foam

strength could be strongly dominated by the core material used.

Figure 6. Comparing mobility reduction factors (MRFs) obtained at the end of each N2-foam generation in different low permeability laminatedBerea sandstone core material (30−280 bar and 50 °C). Logarithmic MRF plotted against subsequent experiment in same core.

Figure 7. Comparing average foam breakthrough times in laminatedBerea sandstone cores during N2-foam generation. Typical gasbreakthrough time during baseline experiment is included forcomparison (i.e., coinjection of N2 and SSW − without surfactant).

Figure 8. Experimental reproducibility in B-ML. Comparing expt. 1with expt. 6 (30 bar and 50 °C) and expt. 2 with expt. 7 (120 bar and50 °C).

Figure 9. Comparing mobility reduction factors (MRFs) obtained atthe end of subsequent N2-foam experiments in B-WL. Differentvariables tested.



Although the physical properties of the cores listed in Table 1indicated that B-WL, B-ML and B-SL appeared to be verysimilar (with respect to average Kw, average porosity, porevolume and core dimensions), expecting relative equal foamstrength, large variations in MRF (20−500) were obtained inthese cores during N2-foam generation. An immediateexplanation to what affected foam strength in these experimentsappeared to be the presence of core heterogeneities, such aslaminations.One significant finding from our core analyses presented in

Appendix A showed that different amounts of laminatedstratifications were present in each core flooded (i.e., number oflamina in B-SL > B-ML > B-WL). The laminas present werefound to exhibit both lower porosity and permeability than thehost rock and also shown to form barriers to foam and fluidflow. The extent to which laminated configurations affects fluidflow have been reported in the literature to depend on factorssuch as the lamina thickness, the amount of lamina relative toscale, and the permeability contrast between lamina and hostrock.29,37−43

6.1. Foam Behavior in Naturally Laminated Cores.Literature on foam flow in naturally layered systems is limited.Results from our foam experiments in laminated core materialindicate that these stratifications affect foam performance.Increased core lamination in this study resulted in weaker N2-foams. Reduced mobility control in cores with increasedlamination were supported by (I) less effective pressure build-ups across the core during foam generation; (II) earlier foambreakthroughs, and; (III) lower MRFs.We speculate if less effective pressure build-up during

coinjection of N2-gas and surfactant solution could havehappened if foam formation and flow were mainly limited tothe more permeable regions of the core. This could have led torapid foam propagation and poor areal sweep. The lowpermeability laminas introduce different degrees of disconti-nuities and compartmentalization to foam flow. With a higherdegree of low permeability laminations present in the corecould indicate that more time is required for the pressuregradient to build-up an allow gas or foam to enter a successivelarger fraction of the pore volume. Early breakthrough may be aconsequence of the foam strength build-up rising too slowly tobe able to stabilize the displacement front properly within coreswith high degree of lamina. In B-WL, with low degree of laminapresent, efficient foam generation and foam propagation closeto ideal flow behavior were observed. This was also supportedby the strongest N2-foams in terms of MRF. The responsesobtained from B-WL are similar to those reported inhomogeneous core material where foam flow in most of thepore space available is observed to take place.27,44

Strong foam seems important to stabilize the displacementfront and prevent early foam breakthrough in low permeabilitylaminated cores. A positive effect of rapid foam propagation at alarger scale, as we see it, is the possibilities of getting improvedmobility control deeper into the reservoir. It should also benoted that the core length of laminated systems could beimportant. A longer core material may allow foam resistance tobuild-up over distance to a point where the front stabilitybecomes restored again. More experiments are needed toconfirm our speculations about foam’s behavior in lowpermeability laminated core material.Experimental studies on foam flow through porous media

have suggested many variables to largely influence foamproperties and performance. Holt et al.32 reported CH4-foam

strength to increase with system pressure (10−290 bar) in aBentheimer sandstone core between ∼1.5-50 bar/m (factor of30) using an AOS C16 surfactant. Slight improved foamstrength with pressure (30, 120, 280 bar) was also observed inthis study in B-ML. The results with pressure are similar to theN2-foams in our recent work in homogeneous and highpermeable Berea sandstone (also generated at 30 and 280bar).27 The effect of pressure on foam strength obtained in ourpresent and recent study was, however, not as significant as thatreported by Holt and co-workers. Yaghoobi45 provides pressuredrop data from CO2-foam experiments in sandstone cores thatranged from ∼1 to 115 bar/m depending on the core, flow rate,surfactant type and concentration used. Chou’s15 N2-foams inBerea sandstone (150−350 mD) were extraordinary strong andranged from 500 to 4000 in resistance factor (RF) when foamexperiments in two Berea cores with different length and flowrates were compared. Interestingly, the huge differences in RFwere suggested to possibly result from the internal variations incore permeability, but without further explanation.Most variables in this study were held constant (i.e., similar

flow rate, foam quality, salinity, surfactant type, concentration,etc.), only changing core material. Our results demonstrate thatpressure gradients could vary from ∼6.5 to 400 bar/m solely bythe core material used. Findings in our study indicate thatmobility control with foam could be strongly dominated bycore heterogeneities, such as laminations. The large variation inMRF obtained between three sandstone cores with differentdegree of lamination could, in our opinion, be an importantrecognition for realistic scaling of foam mobility control to fieldapplications.

6.2. Poor Reproducibility in Laminated Core Material.Restored core permeability or permeability as close as possibleto the absolute permeability was used as criteria before startinga new set of experiment in the same laminated core. Goodreproducibility in subsequent experiment with this procedurewas obtained in our recent work.27 In this paper, poorexperimental reproducibility was observed in laminated corematerial for repeated experiments (Figures 8 and 9). Wespeculate that foam generation reproducibility for repeatedexperiments in B-ML was poor because the starting point ofeach foam experiment was not the same.Zhou et al.46 investigated gas trapping in porous media with a

high resolution 3D X-ray scanner. The gas trapping was studiedin a low permeability Berea sandstone core (Kg ≈ 170 mD)with visible laminations. They found that most of the gas thatentered the laminas became trapped, and remained so.Although the original seawater permeability was able to berestored between 85 and 100% after subsequent experiment inour study, it might be reasonable to believe that trapped gas stillcould be present within the lamina. If gas already was presentwithin the laminas before the next experiment started couldhave contributed to give a faster “homogenization” of foam inthe core during generation. This may have resulted in thesubsequent higher MRFs particularly observed for repeatedexperiments in B-ML.The successive stronger foams and poor experimental

reproducibility observed in laminated core material makes itdifficult and risky to study foam properties in heterogeneouscores. The laminated Berea sandstone material may be relevantto improve understanding of foam in relation to heterogeneousporous media but is not recommended for systematic studies ofvariables affecting foam properties.



6.3. Foam in Low Permeability Porous Media. It seemsevident from the experimental results in this study that the lowcore permeability alone was not detrimental to foam generationand strength. Some authors have suggested that foams existencecould be limited to higher permeabilites,10,12 but this seems notto be the case here. Strong N2-foams in relative lowpermeability sandstone cores have also been reported else-where, even in sandstone cores with permeability as low as 9mD.15−17 Compared to MRFs obtained in our recent work inBerea sandstone material using 0.5 wt % AOS C14-C16surfactant,17,27 the steady state MRF in Berea cores withhomogeneous flow behavior and good experimental reprodu-cibility seems to increase when lowering core permeability(MRF 70 mD > 300mD > 1000 mD). The same observationwas also noticed by Siddiqui et al.16 in Berea sandstone corematerial. Others have reported the foam strength to be anincreasing function of permeability.8,9 In these studies, differentkinds of rock material with varying permeability were comparedagainst each other. One of the factors that might be difficult toaccess when comparing two or more cores with respect topermeability is the degree of core similarity (e.g., lithology, poregeometry, small scale heterogeneities, core dimensions, etc.).The large variations in foam strength and foam performanceseen between three laminated heterogeneous cores with relativesimilar permeability in this study should motivate moreresearch to improve understanding of foam in relation torock type and rock properties.

7. CONCLUSION

N2-foam performance in naturally laminated sandstone coreswith low permeability have been studied at elevated pressureand temperature conditions using AOS surfactant.In-situ N2-foam was generated in all the laminated sandstone

cores flooded. Similar to other work on foam in lowpermeability porous media, our results confirmed that foamwas not limited by low permeability. The results, however,show that the effectiveness of foam to reduce and control gasmobility in sandstone cores with low permeability laminationspresent may be significant. This was reflected by large variationsin MRF (20−500) and foam breakthrough times.Case 1: Weakly laminated core. The strongest foams were

generated in the low permeability core containing low degree oflamination. Efficient foam generation and foam propagationclose to ideal flow behavior were observed.Case 2: Moderate to strongly laminated cores. In two cores

with a higher degree of lamination compared to that in case 1,moderate to weak foams were generated. Consistently earlyfoam breakthroughs in these cores indicated faster foampropagation and less areal sweep. However, 2D imagingconfirmed that improved areal gas sweep after foam placementis possible even in highly laminated rock material. The in situfoams generated in more laminated cores showed reducedmobility control by foam compared to homogeneous rockmaterial.

■ APPENDIX A: ROCK ANALYSES

This appendix contains results obtained from several differentanalyses on used rock material. The rock analyses were first ofall performed as a supplement to characterize the core materialused and to detect possible indications and influences of rockheterogeneity on foam and fluid flow prior to main foamexperiments. The analyses should however be carefully

considered and not overinterpreted as representative indica-tions to our main experiments at higher pressures might belacking.Outcrop Berea sandstone core samples have generally been

widely recognized by the petroleum industry as one of the bestmodel rocks to use for characterizing oil production and foroptimizing enhanced oil recovery (EOR) processes. The mostcommonly used form of Berea has permeability of about 500 to1000 mD and is regarded as relatively uniform. The new supplyof Berea cores that were ordered at the beginning of this studyturned out to be many times lower in permeability than before,typically in the range of 50−200 mD, and with visiblelaminations as seen in Figure A.1. Permeability measurements

perpendicular on the lamina indicated roughly half of thepermeability compared to parallel alignment (∼ 90 vs 45 mD).At Berea’s homepage (www.bereasandstonecores.com), a “splitrock” name is given to this type of sandstone that usually falls inthe lower milliDarcy range. Several techniques were used toanalyze the core material with visible laminations. Ahomogeneous and high permeable (∼1000 mD) Bereasandstone sample was also used in a number of the analysesfor comparison.Five types of analyses were conducted on used batch of rock:

(1) combined X-ray diffraction (XRD)/X-ray fluorescence(XRF) spectrometry to determine minerals and elementcompositions in rock material;47 (2) mercury injection todetermine the distribution of pore sizes;48 (3) SEM and opticalmicroscopy techniques of thin sections from inlet end of eachcore to examine lamina and host rock in terms of porosity,permeability, and mineralogy;29,49 (4) dispersion tests to betterunderstand fluid transport in used cores;50,51 and (5) 2D X-rayscanning for visualization of porous media and fluid flow (i.e.,water/gas injections into sandstone slabs). The use of severaltechniques in combination can be useful and valuable toward abetter description of the used material.Table A1 shows the results from XRD measurements of one

low permeability laminated rock sample compared to a morecommon Berea (1000 mD). The Berea sandstone is mainlycomposted of quarts with different amounts of clay minerals.XRF spectrometry was used on the laminated core to see if wecould detect specific element compositions in the lamina versushost rock. The main elements present within the lamina werefound to be iron, zirconium, silica, and titanium (in this orderbased on their relative intensity from XRF measurements). Ofthe minerals listed in Table A1, siderite (FeCO3) is most likelyone of the dominating minerals present in the lamina. Host

Figure A.1. Visual differences of Berea sandstone samples: (A) lowpermeability core with visible laminations, (B) high permeability core(1000 mD).



www.bereasandstonecores.com

rock, in general, contained all the other minerals found fromthe XRD results in Table A1.A difference in the XRD results between the laminated Berea

and the high permeability Berea is the presence of siderite inthe former and its absence in the latter. Iron-containingminerals were found by Wang et al.52,53 to contribute highsurfactant adsorption and wettability alteration under aerobicconditions compared to reduced conditions of the reservoirenvironment. To evaluate the possible effect that iron couldhave on foam, static experiments with different iron ions (bothFe2+ and Fe3+) added to 0.5 wt % AOS surfactant solution weretested and compared (see Figure A.2). A total ironconcentration of 60 ppm was used in these experiments. Theconcentration level was similar to the maximum dissolved ironconcentration found in the produced water from a Berea corein Wang and Guidry.53 The static foam experiments in FigureA.2 indicated, however, little to no influence of iron on the bulkfoams generated. The surfactant solution produced relativesimilar foam heights independent of the iron ions added.Figure A.3 illustrates the distribution of pore sizes in the

Berea samples found by mercury injection. The average porethroat radius in tested laminated core was found to beapproximately 6 μm. A wider pore size distribution and a largerfraction of smaller pores seems to be present in Berea (lowperm.) compared to Berea (1000 mD). The fraction of smallerpores may indicate the pore sizes in some of the lamina.Analyses through image processing of thin sections were

used to better characterize and differentiate between thedegrees of lamina present in each core used. Back scatterelectron microscopy images (BSE) were used to estimateporosity and permeability within several laminas using themethodology described by Torabi et al.29

Important findings from studying the lamina through imageprocessing techniques included the following:

• Lowest porosity and permeability were found within thelaminas (ϕ = 0−15%, K = 0−50 mD).

• Highest porosity and permeability were found within thehost rock (ϕ = 17−23%, K = 100−250 mD).

• Petrophysical properties found are roughly estimatedvalues and should not be considered as absolute.

• Different degree of lamination were observed in usedcores (B-SL > B-ML > B-WL).

Figure A.4 shows some optical pictures taken of host rockand lamina, respectively.After the foam flooding experiments were performed, the

cores used (i.e., B-WL, B-ML, and B-SL) were sliced lengthwiseand perpendicular to the lamination. X-ray imaging of the coreswas used to confirm that different degree of lamina was presentwithin each core (Figure A.5). The laminas were seen to bethrough-going in all the cores with various thicknesses anddensities along, supporting internal variations in petrophysicalproperties.Figure A.6 shows dispersion curves for the three laminated

cores used in this study. The cores were initially saturated withbrine (containing 1 wt % NaCl) and the tracer response ismeasured by changing the salinity to 2 wt % NaCl. A flow-through electrical conductivity meter measured the conductiv-ity of the effluent leaving the core outlet. Dispersion test of ahigh permeable Berea (standard) was also performed forcomparison. Injection rate of 6 mL/h was used in all tests. Thecores were horizontally oriented.According to the Coats and Smith50 convection-dispersion

(capacitance) model, both dispersivity and flowing fraction ofthe rock is analyzed. The analysis follows a procedure suggestedby Salter and Mohanty51 that detects the flowing fractions aswell as isolated or dead-end pores. If no isolated and dead-endpores in the porous media exist, half of the injected tracer

Table A1. XRD Mineralogy of Berea Sandstone Samples (%of 1 cm3 Rock Sample Analyzed)

core ID quartz kaolinite feldspar chlorite illite/mica

Berea (laminated) 87.5 3.2 1.9 1.7 3.0Berea (1000 mD) 82.7 6.0 5.1 1.1 2.7

plagioclase calcite dolomite sideriteillite/

smectite

Berea (laminated) 0.9 traces 0.9 0.9 0Berea 1000 0.4 0.4 1.5 0 0.2

Figure A.2. Effect of iron on surfactant foamability and stability (SSW reflects the base case without iron).

Figure A.3. Pore size distribution of Berea samples.



concentration should break through after 1 PV tracer injected,and the tracer profile should be symmetrical around this point.The early tracer breakthroughs and tailing of the tracer

profiles as seen for the laminated cores in Figure A.6 indicatelower flowing fractions of these samples compared to thestandard Berea. The weakly and the moderately laminatedBerea sample have dispersivity (0.2 cm) somewhat larger thanliterature data (0.13 cm) report on more homogeneousBerea.54 However, there is a lower flowing fraction andincreasing asymmetry of the dispersion curves with increase inlamination, indicating dendritic or dead-end pores thatexchange brine slow through diffusion. The strongly laminatedBerea (B-SL) shows nonconventional dispersion characteristicwith slow increase in tracer concentration and extensive tailingof the dispersion curve.X-ray scanning was also used in this study to provide

fundamental understanding of fluid flow dynamics in lowpermeability laminated sandstone slabs. The scanner isequipped with a low energy X-ray source (60 kV and 320μA) and a NaI crystal scintillation detector, as well as an X-raycamera, all mounted on linear actuators inside a shieldedcabinet (Figure A.7). The X-ray camera has pixel resolution of0.1 × 0.1 mm (x, y coordinates, respectively). Several laminated

sandstone slabs (10 cm (L) × 5 cm (W) × 1.5 cm (H)) werecoated with epoxy and mounted into the scanner. Inlet andoutlet ends were designed along the sides (Figure A.7C) toensure that fluids were evenly distributed along the whole slabwidth when injected. During fluid injections continuous scanswere taken. The images were subtracted from an initial imagewhere the slab was 100% saturated with water (Sw = 1). Thechanges in attenuation therefore illustrate where fluids actuallyare flowing. All experiments in slabs were conducted at lowpressure (i.e., 2 bar backpressure and 25 °C) due to pressurelimitation of the coated epoxy.Figure A.8 displays a dry scan of a laminated slab. The darker

horizontal regions in the slab represent lamina. Vertical lines inthe picture are noises. The figure illustrates high degree oflamina to be present.Interest was now to use the X-ray scanner to investigate

closer if and how the lamina would influence fluid flow (i.e., bywater and gas flooding in laminated sandstone slabs).Conventional water and gas floods are often influenced bythree main factors, namely, rock heterogeneity (leading towater and gas channeling), gravity segregation due to fluiddensity contrasts (leading to under- or over-riding of theinjected fluids), and unfavorable mobility ratio partly due tofluid viscosity contrasts, which aggravates the negative effects ofthe two first factors. The preceding analyses of the laminatedrock material indicated different physical properties in thelamina compared to host rock to be present (i.e., lower porosityand permeability in the lamina). Also, dispersion testsillustrated that parts of the pore volume in the laminatedcores contibuted less to flow compared with a standard Bereasandstone. Influence on fluid flow dynamics by rockheterogenity was therefore expected.To detect possible influence of core heterogeneity on fluid

flow, gravity-stable water and gas injections in laminated andrelative homogeneous Berea slabs at low injection rate wereperformed and compared (Figure A.9). During these experi-ments, slabs of similar size were used (10 × 5 × 1.5 cm). Theslabs were prepared and coated with epoxy in similar manner,vacuumed, and saturated with water containing 3 wt % NaCl ifnothing else is specified. The gravity-stable water injectedcontained 10 wt % of NaI to enhance X-ray attenuation.Injection rate of tracer water (Figure A.8A) and N2-gas (FigureA.9B) was always set to 3 mL/h (∼0.4−0.6 m/day). Fluidinjections were performed parallel to the lamina (i.e., similar towhat was done in the main foam experiments).During gravity-stable water injection (Figure A.9A), unstable

water displacement was observed for the laminated slab. Thedoped water developed an uneven water front that seemed topropagate faster through the more permeable streaks comparedto the laminated parts. Water breakthrough occurred afterapproximately 0.7 pore volume of NaI−water injected. Little tono change in attenuation within the lamina was generallyobserved when tracer was injected. Most of the laminated partsof the slab remained yellow (i.e., unswept) even after severalpore volumes of NaI−water were injected. For the standardBerea sample more stable water displacement front wasobserved compared to the laminated sample. Water break-through occurred close to one pore volume injected, indicated arelative homogeneous Berea sandstone slab.The gravity-stable water injections illustrate that sample

heterogeneity could influence water flow by water channelingand earlier water breakthrough than expected. As the NaCl−and NaI−water have relative similar viscosity and density

Figure A.4. Optical images showing: (a) host rock without lamina, (b)single structure of lamina, and (c) clusters of cementation typicallyfound in B-SL.



Figure A.5. X-ray images showing different degree of laminations in each core used. The same image setup was used for all three cores for aquantitative comparison. Darker regions in the slab represent lamina. Horizontal lines in the pictures are noises.

Figure A.6. Dispersion tests.

Figure A.7. (A) X-ray scanner, (B) experimental setup with core slab placed in the X-ray scanner, (C) low permeability sandstone slab with visible(horizontal) laminations.

Figure A.8. X-ray scan showing dry sample of a low permeabilitylaminated sandstone slab.



ranges, this should in theory result in a stable water front if theporous media is uniform. The water channeling that isillustrated for the laminated slab demonstrates that conductivitydifferences within the slab are present, which makes it easier forwater to preferentially flow through the more permeableregions than through the laminated parts of the rock sample.An unstable displacement of gas was also observed in the

laminated sample compared to the standard Berea slab (FigureA.9B). During gravity-stable N2-gas injection the gas wasobserved fingering/channeling through the laminated slabcausing early gas breakthrough (after ∼0.15 pore volume ofgas injected) and poor sweep of the sample area. This is atypical example of how we expect the gas to flow in porousmedia with permeability contrasts. For the standard Berea arelative stable gas injection front was observed, also illustratedby gas more uniformly distributed in the slab compared withthe laminated sample. Both slabs seem to be influenced bycapillary end effect as the water saturation remains higher nearthe sample outlet. The capillary end effect is consistent with thetheory that the nonwetting phase (i.e., gas) displaces thewetting phase (i.e., water), in which the capillary forces near theoutlet end are able to counteract the viscous forces acting onthe water. This accumulates water at the end of both slabs.Both gravity-stable water and gas injections into laminated

slabs demonstrate that sample heterogeneity affects fluid flow.The presence and orientation of the laminas illustrated by X-rayscanning seems to act as barriers and compartmentalization tofluid flow. The fact that fluid communication and conductivitywithin the laminated sample are somewhat varying and reducedcould possible influence the oil recovery from these types ofBerea compared to the more standard Berea samples.Observation of foam generation in laminated rock material

was also tested by gas injection into a laminated slab saturatedwith surfactant solution (0.5 wt % AOS surfactant dissolved in10 wt % NaI water). Due to pressure limitation of the coatedepoxy, we were only able to perform experiments at 2 barbackpressure. The SAG (surfactant alternating gas) method wasused to prevent large pressure drop that would overpressurizethe experimental system. In these experiments, the gas

injections were performed horizontally, but still parallel to thelamina.To be able to evaluate foams performance one experiment

was performed only injecting N2-gas into the same slabsaturated with seawater, no surfactant (see Figure A.10). The

gas injection rate was 30 mL/h. Again and similar to FigureA.9B, typical gas finger pattern and poor sweep of the samplearea were observed for the regular gas injection into thelaminated rock sample.When gas was injected into the same slab saturated with

surfactant (Figure A.10 at the right side of the line),experimental observations indicated that foam was able togenerate and reduce gas mobility. Foam was seen to reducefrontal instabilities and improve stability of the gas injectionfront to a larger degree than shown without surfactant. Gas orfoamed gas was observed diverting into successive new areas ofthe tested sample with pore volume gas injected. Even though alack of details down at pore scale exists because of limitedresolution and noise, results showed that improved areal gassweep after foam placement is possible even in highly laminatedrock material.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: [email protected] authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThe authors acknowledge the assistance of Anita Torabi andEivind Bastesen for their geological contributions, and Per ArneOrmehaug for his guidance during some of the 2D X-rayexperiments. The Norwegian Research Council (PETROMAXprogram) is gratefully acknowledged for financial support.

■ NOMENCLATUREAOS alpha olefin sulfonatebar pressure (1 bar =105 Pa)bar/m pressure per meter (1 bar/m = 105 Pa/m)BSE back scatter electron microscopyB-WL Berea-weakly laminated core

Figure A.9. (A) Gravity-stable water injection in laminated (left) andstandard Berea (right) sandstone slab. Pictures from the waterinjection were taken at tracer breakthrough in both cases. (B) Gravity-stable N2-gas injection (yellow) in laminated (left) and standard Berea(right) sandstone slab. Pictures from the gas injection were taken closeto 1 PV injected. The homogeneous core was saturated with 10 wt %NaI during gas injection causing higher attenuation, thus darker(reddish) color. Horizontal lines in the pictures are noises. All slabexperiments were conducted at 2 bar backpressure and 25 °C.

Figure A.10. (Left side of the line) Regular N2-gas injection into watersaturated sample after 0.1 and 1.5 pore volumes injected, respectively.(Right side of the line) N2-gas injection into surfactant saturatedsample after 0.2 and 1.5 PV injected, respectively. All injections wereperformed from left to right at 2 bar backpressure and 25 °C.



mailto:[email protected]

B-ML Berea-moderately laminated coreB-SL Berea-strongly laminated coreC concentrationCo initial concentrationcm centimeter (1 cm =1 × 10−2 m)cm2 square centimeter (1 cm2 = 1 × 10−4 m3)dP differential pressureEOR enhanced oil recoveryH height (i.e., slab thickness)K absolute permeabilityKg absolute permeability to gasKw absolute permeability to waterL lengthmD millidarcy (1000 mD = 1 D = 9.869233 × 10−13 m2)ml milliliter (1 mL = 1 × 10−6 m3)MRF mobility reduction factorPV pore volumeRF resistance factorSEM scanning electron microscopySMR selective mobility reductionSSW synthetic seawaterSw water saturationT temperature (0 °C = 273.15 K)ΔP differential pressurePhi porosityXRD X-ray diffractionXRF X-ray fluorescenceW width2D two-dimensional

■ REFERENCES(1) Bond, D. C.; Holbrook, O. C. Gas Drive Oil Recovery Process, U.S.Patent No. 2,866,507, 1958.(2) Aarra, M. G.; Skauge, A.; Martinsen, H. A. A Breakthrough forEOR in the North Sea. SPE Annual Technical Conference andExhibition, San Antonio, TX, Sept. 29−Oct. 2 2002; Paper SPE 77695.(3) Castanier, L. M. Steam with Additives: Field Projects of theEighties. J. Pet. Sci. Eng. 1989, 2, 193−206.(4) Zhdanov, S. A.; Amiyan, A. V.; Surguchev, L. M.; Castanier, L.M.; Hanssen, J. E. Application of Foam for Gas and Water Shut-off:Review of Field Experience. SPE European Petroleum Conference, Milan,Italy, Oct. 22−24, 1996; Paper SPE 36914.(5) Bernard, G. G.; Holm, L. W. Effect of Foam on Permeability ofPorous Media to Gas. SPE Annual Fall Meeting, Houston, TX, Oct.11−14, 1964; Paper SPE 983.(6) Marsden, S. S.; Kahn, S. A. The Flow of Foam Through ShortPorous Media and Apparent Viscosity Measurements. SPE J. 1966.(7) Raza, S. H. Foam in Porous Media: Characteristics and PotentialApplications. SPE J. 1970.(8) Lee, H. O.; Heller, J. P.; Hoefer, A. M. W. Change in ApparentViscosity of CO2 Foam with Rock Permeability. SPE Reservoir Eng.1991, 421.(9) Mannhardt, K.; Novosad, J. J. Adsorbtion of Foam-FormingSurfactants for Hydrocarbon-Miscible Flooding at High Salinities.FoamsFundamentals and Applications in the Petroleum Industry;Schramm, L., Ed.; American Chemical Society: Washington DC, 1994;pp 265−269.(10) Khatib, Z. I.; Hirasaki, G. J.; Falls, A. H. Effects of CapillaryPressure on Coalescence and Phase Mobilities in Foams FlowingThrough Porous Media. SPE Reservoir Eng. 1988, 919.(11) Zhou, Z. H.; Rossen, W. R. Applying Fractional Flow Theory toFoam Processes at the Limiting Capillary Pressure. 8th SPE/DOESymposium on Enhanced Oil Recovery, Tulsa, OK, April 22−24, 1992;Paper SPE 24180.

(12) Rossen, W. R.; Zhou, Z. H. Modeling Foam Mobility at theLimiting Capillary Pressure. SPE Adv. Technol. Ser. 1995, 3 (1), 146SPE Paper 22627.(13) Rossen, W. R.; Lu, Q. Effect of Capillary Crossflow on FoamImproved Oil Recovery. SPE Western Regional Meeting, Long Beach,CA, June 25−27, 1997.(14) Aarra, M. G.; Ormehaug, P. A.; Skauge, A.; Masalmeh, S. K.Experimental Study of CO2- and Methane-Foam Using CarbonateCore Material at Reservoir Conditions. SPE Middle East Oil and GasShow and Conference, Manama, Bahrain, March 20−23, 2011; PaperSPE 141614.(15) Chou, S. I. Conditions for Generating Foams in Porous Media.66th Annual Technical Conference and Exhibition of SPE, Dallas, TX,Oct. 6−9, 1991; Paper SPE 22628.(16) Siddiqui, S.; Talabani, S.; Saleh, S. T.; Islam, M. R. A LaboratoryInvestigation of Foam Flow in Low-Permeability Berea SandstoneCores. Production Operations Symposium, Oklahoma City, March 9−12,1997; Paper SPE 37416.(17) Vikingstad, A. K.; Aarra, M. G. Comparing the Static andDynamic Foam Properties of a Fluorinated and an Alpha OlefinSulfonate Surfactant. J. Pet. Sci. Eng. 2009, 65, 105−111.(18) Casteel, J. F.; Djabbarah. N.F. Sweep Improvements in CO2

Flooding by Use of Foaming Agents. SPE Reservoir Eng. 1988, 3 (4),1186−1192.(19) Kovscek, A. R.; Bertin, H. J. Foam Mobility in HeterogeneousPorous Media. Transp. Porous Media 2003, 52, 37−49.(20) Zerhboub, M.; Ben-Naceur, K.; Touboul, E.; Thomas, R. MatrixAcidizing: A Novel Approach to Foam Diversion. SPE Prod. Facil.1994, 121−126.(21) Llave, F. M.; Chung, F. T.-H.; Louvier, R. W.; Hudgins, D. A.Foams as Mobility Control Agents for Oil Recovery by GasDisplacement. Proceeding of the 7th SPE/DOE Symposium on EnhancedOil Recovery, Tulsa, OK, 1990; Paper SPE 20245.(22) Behenna, F. R. Acid Diversion from an Undamaged to aDamaged Core Using Multiple Foam Slugs. SPE European FormationDamage Symposium, The Hague, Netherlands, May 15−16, 1995;Paper SPE 30121.(23) Siddiqui, S.; Talabani, S.; Yang, J.; Saleh, S.; Islam, M. R. AnExperimental Investigation of the Diversion Characteristics of Foam inBerea Sandstone Cores of Contrasting Permeabilities. ProductionOperations Symposium, Oklahoma City, March 9−12, 1997; Paper SPE37463.(24) Thompson, K.; Gdanski, R D. Laboratory Study which ProvidesGuidelines for Diverting Acid with Foam. SPE Eastern RegionalMeeting, Lexington, KY, Oct. 22−25, 1991; Paper SPE 23436.(25) Bertin, H. J.; Apaydin, O. G.; Castanier, L. M.; Kovscek, A. R.Foam Flow in Heterogeneous Porous Media: Effect of Crossflow.SPE/DOE Improved Oil Recovery Symposium, Tulsa, OK, Apr. 19−22,1998; Paper SPE 39678.(26) Yaghoobi, H.; Heller, J. P. Effect of Capillary Contact on CO2-foam Mobility in Heterogeneous Core Samples. Permian Basin Oil andGas Recovery Conference, Midland, U.S.A., March 27−29, 1996; PaperSPE 35169.(27) Aarra, M. G.; Solbakken, J.; Skauge, A.; Ormehaug, P. Propertiesof CO2- and N2-Foams as a Function of Pressure. Submitted to J. Pet.Sci. Eng. 2012.(28) FoamsFundamentals and Applications in the Petroleum Industry;Schramm, L., Ed.; American Chemical Society: Washington, DC,1994; pp 173−176.(29) Torabi, A.; Fossen, H.; Alaei, B. Application of SpatialCorrelation Functions in Permeability Estimation of DeformationBands in Porous Rocks. J. Geophys. Res. 2008, 113, B08208DOI: 10.1029/2007JB005455.(30) Aarra, M. G.; Skauge, A. A Foam Pilot in a North Sea OilReservoir: Preparation for a Production Well Treatment. 69th AnnualTechnical Conference and Exhibition, New Orleans, LA, Sept. 25−28,1994; Paper SPE 28599.



(31) Aarra, M. G.; Ormehaug, P. A.; Skauge, A. Foams for GORControl: Improved Stability by Polymer Additives. 9th EAGE EuropeanSymposium on Improved Oil Recovery, The Hague, Oct. 20−22, 1997.(32) Holt, T.; Vassenden, F.; Svorstøl, I. Effect of Pressure on FoamStability; Implications for Foam Screening. SPE/DOE 10th Symposiumon Improved Oil Recovery, Tulsa, OK, April 21−24, 1996; Paper SPE35398.(33) Mannhardt, K.; Novosad, J. J.; Schramm, L. L. ComparativeEvaluation of Foam Stability to Oil. SPE Reservoir Eng. 2000, 23−34.(34) McPhee, C. A.; Tehrain, A. D. H.; Jolly, R. P. S. Foam Floodingof Cores Under North Sea Reservoir Conditions. SPE/DOE EnhancedOil Recovery Symposium, Tulsa, OK, April 17−20, 1988; Paper SPE/DOE 17360.(35) Solbakken, J. S.; Skauge, A.; Aarra, M. G. Supercritical CO2-FoamThe Importance of CO2 Density on Foams Performance. SPEEnhanced Oil Recovery Conference, Kuala Lumpur, Malaysia, July 2−4,2013; Paper SPE 165296.(36) Bai, B.; Griegg, R. B.; Svec, Y.; Wu, Y. Adsorption of a FoamAgent on Porous Sandstone and Its Effect on Foam Stability. ColloidsSurf. A: Physicochem. Eng. Asp. 2010, 353, 189−196.(37) Hesthammer, J.; Fossen, J. Structural Core Analysis From theGullfaks Area, Northern North Sea.Mar. Pet. Geol. 2001, 18, 411−439.(38) Fisher, Q. J.; Knipe, R. J. The Permeability of Faults withinSiliciclastic Petroleum Reservoirs of the North Sea and NorwegianContinental Shelf. Mar. Pet. Geol. 2001, 18, 1063−81.(39) Lothe, A. E.; Gabrielsen, R. H.; Larsen, N.; Bjørnevoll, B. T. AnExperimental Study of the Texture of Deformation Bands: Effects onPorosity and Permeability of Sandstones. Pet. Geosci. 2002, 8, 195−207.(40) Fossen, H.; Bale, A. Deformation Bands and Their Influence onFluid Flow. Am. Assoc. Pet. Geol. Bull. 2007, 91, 1685−1700.(41) Fossen, H.; Schultz, R. A.; Shipton, Z. K.; Mair, K. DeformationBands in SandstoneA Review. J. Geol. Soc. 2007, 164, 755−769.(42) Manzocchi, T.; Ringrose, P. S.; Underhill, J. R. Flow throughFault Systems in High Porosity Sandstones. In Structural Geology inReservoir Characterisation; Coward, M. P., Johnson, H., Daltaban, T.,Eds.; Geological Society of London Special Publication: London,1998; Vol. 127, pp 65−82.(43) Rotevatn, A.; Sandve, T. H.; Keilegavlen, E.; Kolyukhin, D.;Fossen, H. Deformation Bands and Their Impact on Fluid Flow inSandstone Reservoirs: The Role of Natural Thickness Variations.Geofluids 2013, DOI: 10.1111/gfl.12030.(44) Simjoo, M.; Dong, Y.; Andrianov, A.; Talanana, M.; Zitha, P. L.J. Novel Insight into Foam Mobility Control. SPE J. 2013, 416−427.(45) Yaghoobi, H. Experimental Evaluation of CO2-Foam Mobility inHeterogeneous Porous Systems. Ph.D. dissertation, New Mexico Instituteof Mining and Technology, Socorro, NM, 1995.(46) Zhou, N.; Matsumoto, T.; Hosokawa, T.; Suekane, T. Pore-Scale Visualization of Gas Trapping in Porous Media by X-ray CTScanning. Flow Meas. Instrum. 2010, 21, 262−267.(47) X-Ray Diffraction; Warren, B. E., Ed.; Addison-WesleyPublishing Company: Boston, 1969.(48) Ritter, H. L.; Drake, L. C. Pore-Size Distribution in PorousMaterials; American Chemical Society: Washington DC, Sept. 1945;,pp 782−786.(49) Goldstein, J.; Newbury, D. E.; Joy, D. C.; Lyman, C. E.; Echlin,P.; Lifshin, E.; Sawyer, L.; Michael, J. R. Scanning Electron Microscopyand X-Ray Microanalysis, 3rd corrected ed.; Springer: New York, 2003.(50) Coats, K. H.; Smith, B. D. Dead-End Pore Volume andDispersion in Porous Media. Trans. AIME 1963, 231, 73−84.(51) Salter, S. J., and Mohanty, K. K. Multiphase Flow in PorousMedia: I. Macroscopic Observations and Modeling. SPE AnnualTechnical Conference and Exhibition, New Orleans, LA, 1982; PaperSPE 110177.(52) Wang, F. H. L. Effects of Reservoir Anaerobic, ReducingConditions on Surfactant Retention in Chemical Flooding. SPEReservoir Eng. 1993, 9 (2), 108−116.

(53) Wang, F. H. L.; Guidry, L. J. Effect of Oxidation-ReductionCondition on Wettability Alteration. SPE Form. Eval. 1994, 9, 140−148.(54) Garnes, J. M.; Mathisen, A. M.; Scheie, Å.; Skauge, A. CapillaryNumber Relations for Some North Sea Reservoir Sandstones. SPE/DOE Seventh Symposium on Enhanced Oil Recovery, Tulsa, OK, April1990; pp 879−889, Paper SPE/DOE 20264.



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Foam Performance in Low Permeability Laminated Sandstones