silica nanofluid flooding for enhanced oil recovery in sandstone rocks

The ultimate recovery of initial oil in place increased by 13.28% when using tertiary flooding of silica nanofluid compared to the recovery achieved by water flooding alone.. Two floodin

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Silica nanofluid flooding for enhanced oil recovery in sandstone rocks

Magda I Youssifa, Rehab M El-Maghrabyb,⇑, Sayed M Salehc, Ahmed Elgibalyd

a

Petroleum Department and Gas Technology, Faculty of Engineering, British University, Egypt

b Chemical Engineering and Petroleum Refining Department, Faculty of Pet and Min Engineering, Suez University, Egypt

c

Department of Science and Mathematics, Faculty of Pet and Min Engineering, Suez University, Egypt

d

Petroleum Engineering Department, Faculty of Pet and Min Engineering, Suez University, Egypt

a r t i c l e i n f o

Article history:

Received 26 September 2016

Revised 26 December 2016

Accepted 24 January 2017

Available online xxxx

Keywords:

Enhanced oil recovery (EOR)

Porous media

Dispersed silica nanoparticle

Nanoflooding

Nanoparticles stability

Nanofluid

a b s t r a c t

Enhanced oil recovery is proposed as a solution for declining oil production One of the advanced trends

in the petroleum industry is the application of nanotechnology for enhanced oil recovery Silica nanopar-ticles (SiNPs) are believed to have the ability to improve oil production, while being environmentally friendly and of natural composition to sandstone oil reservoirs

In our work, we investigated the effect of silica nanoparticles flooding on the amount of oil recovered Experiments were carried using commercial silica of approximately 20 nm in size We used sandstone cores in the core flooding experiments For one of the cores tertiary recovery is applied where brine imbi-bition was followed by nanofluid imbiimbi-bition While in the other cores secondary recovery was applied where primary drainage is directly followed by nanofluid imbibition We investigated the effect of con-centration of nanofluid on recovery; in addition, residual oil saturation was obtained to get the displace-ment efficiency Silica nanofluid of concentration 0.01 wt%, 0.05 wt%, 0.1 wt% and 0.5 wt% were studied The recovery factor improved with increasing the silica nanofluid concentration until optimum concen-tration was reached The maximum oil recovery was achieved at optimum silica nanoparticles concentra-tion of 0.1 wt% The ultimate recovery of initial oil in place increased by 13.28% when using tertiary flooding of silica nanofluid compared to the recovery achieved by water flooding alone Based on our experimental study, permeability impairment was investigated by studying the silica nanoparticles con-centration, and the silica nanofluid injection rate The permeability was measured before and after nano-fluid injection This helped us to understand the behavior of the silica nanoparticles in porous media Results showed that silica nanofluid flooding is a potential tertiary enhanced oil recovery method after water flooding has ceased

Ó 2017 Egyptian Petroleum Research Institute Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

1 Introduction

Due to the declining oil production in many oil reservoirs,

advanced techniques are necessary to continue oil production

and to recover more oil in place[1] Among those techniques are

the enhanced oil recovery techniques The use of nanotechnology

for enhanced oil recovery is considered to be a new emerging

trend This nanotechnology application began at the end of

1980’s and has been developed to synthesize new nanomaterials

by rearranging atoms and molecules[2] Based on the small size

of the nanoparticles (1–100 nm), the optical, thermal, chemical,

and structural properties of the nanomaterial differs totally from those displayed by either their atoms or the bulk materials[3] For enhanced oil recovery purpose, the smaller the nanoparticle size, the larger the surface area, and the larger the contact surface between the nanoparticles and the oil phase This allows better interaction between the nanoparticles and the oil phase for further recovery[4] The most commonly used nanoparticles in enhanced oil recovery are silica nanoparticle (SiNPs) About 99.8% of silica nanoparticle are silicone dioxide, which is the main component

of sandstone Silica nanoparticles are an environmentally friendly material compared to other nanomaterials In addition, silica nanoparticles are cheap and their chemical behavior could be easily controlled by surface modification

There are possible displacement mechanisms, by which silica nanoparticle could enhance oil production, are believed to occur The first mechanism is the disjoining pressure mechanism This mechanism occurs when silica nanoparticle are present in the

dis-http://dx.doi.org/10.1016/j.ejpe.2017.01.006

1110-0621/Ó 2017 Egyptian Petroleum Research Institute Production and hosting by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Peer review under responsibility of Egyptian Petroleum Research Institute.

⇑ Corresponding author.

E-mail addresses: magda.ibrahim@bue.edu.eg (M.I Youssif), rehab.elmaghraby@

Contents lists available atScienceDirect

Egyptian Journal of Petroleum

j o u r n a l h o m e p a g e : w w w s c i e n c e d i r e c t c o m

Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017),http://dx

persing medium, so these particles tend to rearrange themselves in

a wedge-shaped film in contact with the discontinuous oil phase

[5,6] The wedge film acts to detach the oil phase from the rock

sur-face, hence recovering more oil as illustrated inFig 1 The

disjoin-ing pressure represents the pressure difference between the

pressure in the wedge film region and that in the bulk liquid[7]

This pressure is driven by Brownian motion and the electrostatic

repulsion between molecules

The second mechanism is the Log-Jamming mechanism Due to

the smaller size of pore throats and the constant differential

pres-sure in the pores, the velocity of the silica nanofluid will increase at

the pore throat compared to the pore body This may cause the

water molecules to move faster than the silica nanoparticles,

caus-ing the nanoparticles to accumulate and eventually block the pore

entrance This may force the water flow to change pass to other

non-invaded pores, possibly oil filled, resulting in more oil

recov-ery The third mechanism is the wettability alteration mechanism

Silica nanoparticles have the ability to change rock wettability and

to reduce the interfacial tension and the contact angle between

two immiscible fluids[1,8–10]

Oil recovery by nanofluid flooding is affected by various

param-eters such as nanofluid concentration, particle size, injection rate,

and slug size Nanofluid concentration is considered one of the

major parameters to enhance oil recovery The goal of this study

is to investigate the effect of silica nanofluids as an enhanced oil

recovery agent in Sandstone rocks

2 Materials and methodology

2.1 Materials

Three Sandstone cores of different permeability ranges were

used The properties of the cores are listed inTable 1 Black oil of

32.5 API and 4.6 cp obtained from the North Sea was used in the

flooding experiments The synthetic brine used is of concentration

of 3.0 wt% NaCl (GPR grade, purity 99.5%, from Alpha Chemicals

Company)

Commercial hydrophilic mono dispersed silica (SiO2)

nanoparti-cles of 370 m2/g specific area were used in the experiments The

average particle size was 22 nm They consist of basically more

than 99.8% of silicon dioxide (SiO2) (Al2O3) 60.06%, Titanium

Dioxide (TiO2)60.03%, Hydrogen Chloride (HCl) 60.028% and other traces elements

Hydrophilic silica nanoparticles were suspended in 3 wt% brine; this solution will be referred as silica nanofluid The Nanofluid was prepared with different concentrations, 0.01 wt%, 0.05 wt%, 0.1 wt

%, 0.2 wt% and 0.5 wt% Each solution was mixed by using magnetic stirrer for several minutes To avoid precipitation of nanoparticles from solution, ultrasonic probe (400 W and 0.5 Hz) is used for 1 h

to assurance the homogeneity and stability of prepared solutions The properties of the used nanofluid at different silica nanoparti-cles concentrations are listed inTable 2

2.2 Methodology The equipment used for cores flooding was manufactured by Vinci Company, in France The experimental set-up is shown in Fig 2 Two flooding scenarios were studied; one with silica nano-fluid as a secondary recovery technique, and the other where silica nanofluid are used as a tertiary recovery technique

In the first scenario, silica nanofluid were used as a tertiary recovery technique Core# 1 was first cleaned and dried then placed in glass desiccator to be fully saturated with brine of 3 wt

% NaCl concentration The weight of the core was recorded many times until the weight remained constant The core was placed in the core holder and black oil injection took place The injection flow rate was increased until irreducible water saturation was reached At this point the core was saturated with oil Then imbibition process was initiated by using brine to displace oil at injection rate of 0.5 ml/min, and then continued until no more oil produced Pore volume of the injected brine was 1.77 PV At this stage, residual oil saturation (Sor1) was determined, and recovery factor was calculated The next step was to continue injection

by nanofluid of different concentration at injection rate of 0.5 ml/min At this stage, residual oil saturation (Sor2) was deter-mined again, and recovery factor was calculated to determine how much oil would be produced at this concentration

The displacement efficiency was calculated from the following equation:

ED¼ 1 Sor2

Sor1

Fig 1 Illustration of nanoparticle schematic and structural disjoining pressure gradient mechanism among solid, oil and nanofluids as aqueous phase. Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017),http://dx

where, EDis displacement efficiency, Sor1is residual oil saturation

after brine floods, and Sor2is residual oil saturation after nanofluid

floods

In the second scenario, Core # 2 and Core# 3 were tested using

silica nanofluid as secondary recovery method The previous

flood-ing steps mentioned in scenario 1 were repeated The only

differ-ence was that the imbibition step using brine was not followed

immediately by silica nanofluid imbibition Instead after the

imbi-bition of the core with brine the core was cleaned, then dried and

saturated with brine The drainage process was initiated by oil

injection in the core till irreducible water saturation is reached,

after which the silica nanofluid imbibition stared immediately till

we reach residual oil saturation Different silica nanofluid

concen-tration was investigated

Injecting Silica nanoparticles through the pores of the cores may

lead to particle retention in some cases[11] Consequently many

parameters should be taken into consideration to eliminate

perme-ability impairment to minimum level Concentration of

nanoparti-cle suspension, well-dispersion solution, injection rate, and pore

volume injected are the most important parameter affecting on

the permeability impairment[12] The permeability was measured before and after nanofluid injection on Core# 1, Core# 2, and Core#

3 to make sure that permeability impairment or other reduction in reservoir properties didn’t exceed a desired value

3 Results & discussion Tertiary recovery is performed on Core# 1, after imbibition by water flooding; Core# 1 was flooded by silica nanofluid of different concentration.Fig 3showed the relation between PV injected and recovery factor at each concentration for Core# 1 The residual sat-uration after water flooding and silica nanofluid flooding for core#

1 and core# 2 are listed inTable 3 It was observed that the injec-tion of silica nanofluid in the core enhances oil producinjec-tion, espe-cially as the silica concentration increases The higher the silica concentration, the higher the amount of recovered oil up to an optimum silica nanofluid concentration after which the oil recov-ery decrease It is believed that permeability impairment was the cause of the reduction in oil recovery at high concentration because of the locking of the tiny pores of the core plug The use

of silica nanoparticles following brine flooding increased the oil recovery factor from 53.1% in the case of water flooding alone to 66.40% following silica nanofluid injection at 0.1 wt% silica concen-tration as a tertiary recovery

Secondary recovery is performed on Core# 2, where the primary drainage stage is followed by direct silica nanofluid imbibition Dif-ferent silica nanoparticles concentrations were used to reach an optimum concentration that will maximize the oil recovery factor

Table 1

The properties of the sandstone cores used in our experiments.

Permeability b

Sw i

a

Porosity is measured by Helium Porosimeter.

b

Permeability is measured by Klinkenberg method.

Table 2

Silica nanofluid properties.

Fig 2 Experimental set up schematic: (1) Graduated tube (2) Prep Pump (3) Injection pipe (4) Core holder (5) Core plug (6) Sleeve pressure (7) Fluid accumulator (8) Carry over fluid accumulator (9) Hydraulic pump.

Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017),http://dx

As shown inFig 4, the optimum silica concentration was 0.1 wt%.

At this concentration an oil recovery factor of 54% was achieved

compared to an oil recovery factor of 41.3% in the case of water

imbibition alone

Introducing silica nanoparticles to the oil/water system was

observed to lower the interfacial tension (IFT), then the potential

to produce more trapped oil[13,14] This may be due to the

hydro-philic part of the silica nanoparticles present in the aqueous phase

and the hydrophobic part exists in the oil phase, so the adhesive

forces between the two phases increases and the IFT decreases

It was observed that within the range of silica nanoparticles

concentration of 0.2 and 0.5 wt% there is a drop in the oil recovery

when compared to the trend of other silica concentrations As silica

surface is completely hydroxylated and each Si atom on the surface

is surrounded by OH groups[15], the surface charge of the silica

nanoparticles were determined in terms of protonation and

depro-tonation of these silanol groups The resultant net charge of silica nanoparticles surface controls to which extent the repulsion forces keep particles dispersed in solution The drop in the oil recovery, in case of increasing the concentration of silica nanoparticles in pres-ence of constant electrolyte concentration, may be due to the increment of the deprotonation process of silanol groups at the surface of nanoparticles which accelerates the coagulation process forming a cumulative particles that block the pores hindering oil production

Comparing flooding in Core# 1 and flooding in Core# 2 we can see that there is no difference in the recovery when using silica nanofluid in a secondary recovery technique or in a tertiary recov-ery technique, as at the end we get nearly the same results As we can see fromFig 3an increase of 13.28% in the oil recovery was achieved when the silica tertiary recovery technique was followed

by water secondary recovery technique in Core #1 We can also see

0 10 20 30 40 50 60 70

PV injected

WF

NF, conc 0.01wt.%

NF, Conc 0.05%

NF, conc 0.1wt.%

NF,conc 0.5 wt.%

Fig 3 Recovery factor (RF) vs pore volume (PV) injected for Core # 1

Table 3

Residual oil saturation (S or ) obtained after water flooding and Silica nanofluid flooding.

Oil saturation [ So], fraction

Core

No.

Before water

flooding

After water flooding

After 0.01 wt%

nanoflooding

After 0.05 wt%

nanoflooding

After 0.1 wt%

nanoflooding

After 0.2 wt%

nanoflooding

After 0.5 wt% nanoflooding

0 10 20 30 40 50 60

PV injected

WF

NF, Conc 0.05wt.%

NF, conc 0.1wt%

NF, conc 0.2wt%

NF, conc 0.5wt.%

Fig 4 Recovery factor (RF) vs pore volume (PV) injected for Core # 2.

Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017),http://dx

fromFig 4, an increase of 12.7% in oil recovery factor was achieved

when using silica nanofluid flooding as a secondary recovery

tech-nique compared to using water flooding as a secondary recovery

technique in Core# 2 This result will favour using water flooding

as a secondary recovery technique due to its low price and

feasibil-ity at the start of the recovery, then silica nanofluid flooding can be

used as a tertiary technique to utilize the benefit of silica

nanopar-ticles in enhancing the oil production

In addition, recovery achieved by nanofluid of concentration

0.5 wt% is less than that achieved by water flooding This is mainly

due to the accumulation of the silica nanoparticles through the

pores and pores throats, hence blocking the pores Consequently,

this concentration could not be applicable as it could damage the

rock morphology

Core flooding is carried on Core# 3 to investigate the effect of

silica nanofluid on water breakthrough As shown inFig 5, it was

observed that silica nanofluid has an effect on delaying water

breakthrough; hence volumetric sweep efficiency increase and

more oil could be produced as confirmed also by Li and Torsaeter

[10] The experiments were done at concentration of 0.1 wt% and

at constant injection rate of 0.5 ml/min

In general, when the concentration of the silica nanofluid

increases within specific range, the random movement of particles

increases[7], thereby repulsive forces between molecules increase

and the rock wettability is strongly altered This will increase the

amount of oil that could be recovered However, as the concentra-tion of nanoparticle in fluid increase the porosity and permeability

is affected causing permeability impairment [12] Hence, the important to work at 0.1 wt% silica nanofluid concentration, to achieve the maximum oil recovery with minimum permeability impairment

3.1 Permeability impairment Permeability was calculated using Darcy equation The effect of nanoparticles concentration and injection rate on the permeability impairment was studied

3.1.1 Effect of concentration Based on the results shown inTable 4, as the concentration of silica nanofluid increases the absolute permeability decreases, at constant nanofluid injection rate of 0.5 ml/min Maximum perme-ability reduction of 60% due to nanofluid injection was observed at 0.5 wt% silica nanofluid concentrations This result justifies that at 0.5 wt% nanofluid concentration the oil recovery by silica nanofluid was the lowest of all concentration due to pore blockage 3.1.2 Effect of injection rate

Nanoparticles retention is affected by the silica nanofluid injec-tion rate Due to the high velocity and the difference in density

0

20

40

60

80

100

0 1 2 3 4 5 6

PV injected

WF

NF, conc

0.1wt.%

Fig 5 Water cut vs pore volume (PV) injected for Core# 3.

Table 5

Effect of silica nanoparticle injection rate on permeability impairment at 0.05 wt% silica concentration.

Core No k absolute before nanofluid injection Silica nanofluid injection rate k absolute after nanofluid injection k reduction

Table 4

Effect of silica nanoparticle concentration on permeability impairment at 0.5 ml/min injection rate.

Core No k absolute before nanofluid injection Silica nanofluid concentration k absolute after nanofluid injection k reduction

Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017),http://dx

between the silica nanoparticle and the brine, nanoparticles settle

down causing pore blockage All the parameters are kept constant

except injection rate.Table 5showed that the permeability

impair-ment increases as the injection rate increases

4 Conclusions

 Silica nanofluid is environmentally compatible with sandstone

rocks

 The amount of recovered oil with tertiary recovery using silica

nanofluid is slightly higher than that obtained by secondary

recovery method using silica nanofluid This makes water

flood-ing followed by silica nanofluid floodflood-ing an effective recovery

scenario and an economically wise

 Oil recovery factor increases by increasing the silica nanofluid

concentration up to an optimum concentration of 0.1 wt%

above, which the amount of recovered oil will decrease, with

increasing the silica nanofluid concentration

 Silica nanofluid concentration of 0.1 wt% is the recommended

concentration to achieve the maximum oil recovery with

mini-mum permeability impairment, hence keeping the rock

mor-phology undamaged

 Silica nanoparticles have the potential to increase oil recovery

by delaying the water breakthrough hence more oil could be

produced

 Injecting the silica nanofluid at low injection rate decreases

per-meability impairment, while using silica nanoparticles at high

concentration will increase the permeability impairment but

will increase oil recovery up to a certain value

Acknowledgment

Special thanks to Lab Engineer Walid, for his valuable

assis-tance in the laboratory Laboratory work was conducted at the

British University in Egypt

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Please cite this article in press as: M.I Youssif et al., Silica nanofluid flooding for enhanced oil recovery in sandstone rocks, Egypt J Petrol (2017),http://dx