**1. Introduction**

The advancement of nanotechnology attract researchers interest for its application in oil and gas that include the application for enhanced oil recovery, exploration, drilling, completion, well logging, chemical stabilizer, conformance control, heavy oil, stimulation and fines migration control [1–13]. The unique properties of nanoparticles comprises of extremely high surface area compared to their small sizes, thermally stable, high potential to alter the wettability of the reservoir formations, modify rock surface charges and associated impact on the rheological properties of suspensions [14] that showed potentials to enhance extraction of

hydrocarbons. Silica nanoparticles, SiO2 for example, can be found in most nontoxic inorganic materials which also the main component of sandstone rock, and is more environmental friendly compared to chemical based materials. Nanoparticles have showed remarkable performance in fixing the formation fines during fracturing activities [12]. Several studies suggested the nanoparticles has the effect of strengthening the attractive forces with regards to the repulsive forces and prevent the detachment of fines particles from the pore walls [15].

Nanoparticles are very small in nature with size range between 1 and 100 nm [16] which permits this tiny particles to flow in the porous media and show distinctive behavior which fascinating from petroleum engineering perspective. During nanoparticles transport in porous media, the physicochemical attraction between particles and the pore walls can lead to adsorption or retention that occurs as reversible and irreversible [17, 18]. Adsorption in porous media can create major issue and need to be control to avoid significant formation damage. Abdelfatah described; three different mechanisms were taken place when nanoparticles interact in the pores. These interactions are surfaces deposition, mono-particle plugging and multi-particles plugging [19]. The surface deposition interactions are dominated by five type of forces; the attractive potential force of Van der Waals, repulsion force of electric double layers, Born repulsion, acid–base interaction, and hydrodynamics [20]. The adsorption of nanoparticles and the pore walls will occur when the total force is negative, where the attraction is larger than repulsion between nanoparticles and pore walls.

The mono-particle plugging or screening or mechanical entrapment occur when larger particle block at the narrow pores. Injecting large volume of nanoparticles can lead to mono-particle plugging. Multi-particles plugging or log-jamming mechanism is similar to mono-particle plugging but the blocking occurs at pore channel larger than nanoparticles size. Log-jamming happen when nanoparticles flow from pores to narrow pore throat. Nanoparticles interaction between the particles itself can cause aggregation and gelation and the significantly block the pore throat if the aggregate size much bigger than pore throat. The adsorption of nanoparticle on the pore walls also depends on the type and pH of nanoparticles, rock clay content as well as the rock wettability [21]. The advantage of nanoparticles adsorption, instead, it contributed to the alteration of rock wettability that is desirable for

**241**

water.

*Aggregation of Partially Hydrophilic Silica Nanoparticles in Porous Media: Quantitative…*

enhanced oil recovery [22–25]. Nanoparticles specifically silica nanoparticles on the other hand, are not stable in salts water and aggregates at elevated temperature, high concentration and at high injection rates that can lead to substantial permeability impairment [17, 24, 26–28]. **Figure 1** shows the illustration of nanoparticles

This experimental work investigates the aggregation of partially hydrophilic silica nanoparticles, SiO2 in porous media. The standard method for silica nanoparticles concentration measurement using UV-Vis spectrophotometer is not suitable, and hence more reliable quantitative and qualitative methods were developed. Core flooding pressure drops and particles size analysis of treated Buff Berea cores provide quantitative information supported by qualitative measurement of Field Emission Scanning Electron Microscope (FESEM) and micromodel test. The pressure drops value showed closed agreements with particles size during silica nanoparticles injection and brine post flush, visualization of silica nanoparticles in micromodel. FESEM analysis suggested the partially hydrophilic silica nanoparticles used in this experimental work showed minimal aggregation with insignificant

Partially hydrophilic silica nanoparticles (SiO2) supplied by commercial nanomaterials company using code name NPN-ST. This nanoparticles was selected based the requirement of this research work in terms of size and solubility in water and selected solvent. NPN-ST supplied at 30% active concentration with average size of 12 nm and pH 5. NPN-ST was diluted in mutual solvent at 0.05% concentration and

The turbidity reading is in the low range between 0.95 and 1.98 NTU. **Figure 2**

Formation brine used in this study is mixture of major ion salts prepared in deionized water. CaCl2, MgCl2, KCl and NaCl salts were mixed in the appropriate proportions to make up 1.5 wt% formation water salinity. Brine sample was filtered with the Millipore vacuum filter through a 47 mm, 0.45 micron nominal pore opening cellulose filter. **Table 1** shows the brine composition of synthetic formation

shows the particles size distribution and visual observation of NPN-ST after 24 hours sustained as clear solution and did not show any forms of precipitation. **Figure 3** shows the Transmission Electron Microscopy (TEM) image of NPN-ST solution at 20 and 100 nm scale which comparable with most common silica

the solution undergoes sonication in ultrasonic bath for at least 40 minutes. NPN-ST stability in the carrier fluid before and after 24 hours aged at room temperature and 60°C was determined through visual observation, turbidity test and particle size distribution measurement. The particle size of NPN-ST slightly increased from 24 nm to ~27 nm and 35 nm after kept for 24 hours at room temperature and at 60°C respectively. The incremental of particle size is minor which is

*DOI: http://dx.doi.org/10.5772/intechopen.92101*

interactions mechanisms in porous media.

permeability impairment.

**2. Materials and methods**

*2.1.1 Nanofluids*

nanoparticles materials.

*2.1.2 Fluid samples*

**2.1 Materials for core flooding**

within the accepted size required for this study.

**Figure 1.** *Nanoparticles interactions mechanisms in porous media [19].* *Aggregation of Partially Hydrophilic Silica Nanoparticles in Porous Media: Quantitative… DOI: http://dx.doi.org/10.5772/intechopen.92101*

enhanced oil recovery [22–25]. Nanoparticles specifically silica nanoparticles on the other hand, are not stable in salts water and aggregates at elevated temperature, high concentration and at high injection rates that can lead to substantial permeability impairment [17, 24, 26–28]. **Figure 1** shows the illustration of nanoparticles interactions mechanisms in porous media.

This experimental work investigates the aggregation of partially hydrophilic silica nanoparticles, SiO2 in porous media. The standard method for silica nanoparticles concentration measurement using UV-Vis spectrophotometer is not suitable, and hence more reliable quantitative and qualitative methods were developed. Core flooding pressure drops and particles size analysis of treated Buff Berea cores provide quantitative information supported by qualitative measurement of Field Emission Scanning Electron Microscope (FESEM) and micromodel test. The pressure drops value showed closed agreements with particles size during silica nanoparticles injection and brine post flush, visualization of silica nanoparticles in micromodel. FESEM analysis suggested the partially hydrophilic silica nanoparticles used in this experimental work showed minimal aggregation with insignificant permeability impairment.

### **2. Materials and methods**

#### **2.1 Materials for core flooding**

#### *2.1.1 Nanofluids*

*Nano- and Microencapsulation - Techniques and Applications*

the detachment of fines particles from the pore walls [15].

ticles and pore walls.

hydrocarbons. Silica nanoparticles, SiO2 for example, can be found in most nontoxic inorganic materials which also the main component of sandstone rock, and is more environmental friendly compared to chemical based materials. Nanoparticles have showed remarkable performance in fixing the formation fines during fracturing activities [12]. Several studies suggested the nanoparticles has the effect of strengthening the attractive forces with regards to the repulsive forces and prevent

Nanoparticles are very small in nature with size range between 1 and 100 nm [16] which permits this tiny particles to flow in the porous media and show distinctive behavior which fascinating from petroleum engineering perspective. During nanoparticles transport in porous media, the physicochemical attraction between particles and the pore walls can lead to adsorption or retention that occurs as reversible and irreversible [17, 18]. Adsorption in porous media can create major issue and need to be control to avoid significant formation damage. Abdelfatah described; three different mechanisms were taken place when nanoparticles interact in the pores. These interactions are surfaces deposition, mono-particle plugging and multi-particles plugging [19]. The surface deposition interactions are dominated by five type of forces; the attractive potential force of Van der Waals, repulsion force of electric double layers, Born repulsion, acid–base interaction, and hydrodynamics [20]. The adsorption of nanoparticles and the pore walls will occur when the total force is negative, where the attraction is larger than repulsion between nanopar-

The mono-particle plugging or screening or mechanical entrapment occur when larger particle block at the narrow pores. Injecting large volume of nanoparticles can lead to mono-particle plugging. Multi-particles plugging or log-jamming mechanism is similar to mono-particle plugging but the blocking occurs at pore channel larger than nanoparticles size. Log-jamming happen when nanoparticles flow from pores to narrow pore throat. Nanoparticles interaction between the particles itself can cause aggregation and gelation and the significantly block the pore throat if the aggregate size much bigger than pore throat. The adsorption of nanoparticle on the pore walls also depends on the type and pH of nanoparticles, rock clay content as well as the rock wettability [21]. The advantage of nanoparticles adsorption, instead, it contributed to the alteration of rock wettability that is desirable for

**240**

**Figure 1.**

*Nanoparticles interactions mechanisms in porous media [19].*

Partially hydrophilic silica nanoparticles (SiO2) supplied by commercial nanomaterials company using code name NPN-ST. This nanoparticles was selected based the requirement of this research work in terms of size and solubility in water and selected solvent. NPN-ST supplied at 30% active concentration with average size of 12 nm and pH 5. NPN-ST was diluted in mutual solvent at 0.05% concentration and the solution undergoes sonication in ultrasonic bath for at least 40 minutes.

NPN-ST stability in the carrier fluid before and after 24 hours aged at room temperature and 60°C was determined through visual observation, turbidity test and particle size distribution measurement. The particle size of NPN-ST slightly increased from 24 nm to ~27 nm and 35 nm after kept for 24 hours at room temperature and at 60°C respectively. The incremental of particle size is minor which is within the accepted size required for this study.

The turbidity reading is in the low range between 0.95 and 1.98 NTU. **Figure 2** shows the particles size distribution and visual observation of NPN-ST after 24 hours sustained as clear solution and did not show any forms of precipitation. **Figure 3** shows the Transmission Electron Microscopy (TEM) image of NPN-ST solution at 20 and 100 nm scale which comparable with most common silica nanoparticles materials.

#### *2.1.2 Fluid samples*

Formation brine used in this study is mixture of major ion salts prepared in deionized water. CaCl2, MgCl2, KCl and NaCl salts were mixed in the appropriate proportions to make up 1.5 wt% formation water salinity. Brine sample was filtered with the Millipore vacuum filter through a 47 mm, 0.45 micron nominal pore opening cellulose filter. **Table 1** shows the brine composition of synthetic formation water.

#### **Figure 2.**

*Particle size and visual observation of NPN-ST at initial and after 24 hours aged at room temperature and 60°C.*

#### **Figure 3.**

*Image of 0.05% NPN-ST under transmission electron microscopy (TEM): (a) at 100 nm scale and (b) at 20 nm scale.*


#### **Table 1.**

*Salt composition for formation brine.*

#### *2.1.3 Core samples*

Buff Berea cores of 3.8 cm in diameter and 7.5 cm in length (and 2 sets of core with 14.0 cm in length), permeability range between 200 and 400 mD that contained mixture of clays were used in this study. Five sets of core flood tests were conducted and details of core properties assigned for each experiment are listed in **Table 2**. **Table 3** shows the Buff Berea core detail mineralogy measured by X-Ray Diffraction (XRD) test.

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*Aggregation of Partially Hydrophilic Silica Nanoparticles in Porous Media: Quantitative…*

**Porosity (%)**

**Core Calculated whole rock composition (weight %)**

**Kaolinite Chlorite Illite Mixed** 

B1–10 3.84 7.40 23.35 386.79 20.10 30 B3–21 3.84 7.44 23.20 328.89 20.02 30 L1 3.84 14.18 N.D.1 N.D.1 37.90 30 B7-16 3.84 7.44 23.50 325.42 19.82 60 L2 3.84 14.55 N.D.1 N.D.1 38.89 60

**Air permeability (md)**

**Quartz Plagioclase K-Feldspar Calcite Dolomite Siderite Pyrite**

79.2 4.3 1.9 0.4 1.1 0.9 1.0 **Clay fraction Clay fraction (clay typing, weight %)**

36.2 19.7 33.2 7.9 2.5 10.7

**layer (I/S)**

**Pore volumes (ml)**

**Smectite Total clay**

**Test temperatures (°C)**

The dry weight of the core was measured before brine saturation. Core was saturated in desiccator with formation brine until all air trapped were removed. The core was then put in saturator for further saturation at 2000 psi for 24 hours. The saturated weight of the core was measured after saturation to calculate the core pore volume (PV) by gravimetric method. The core was carefully unloaded from saturator, into core holder and subject to 1500 psi confining pressure applied with mineral oil using automatic confining pressure pump. The back pressure was set at 200 psi and temperature set at 30 and 60°C. The core was flooded with brine for at least 2 pore volumes or until pressure stabilize at 0.5, 1.0 and 1.5 ml/min. The derived pressure drops data were used to calculate absolute permeability to water using Darcy's Law. The core flooding test was conducted using Formation Response Test (FRT)

equipment model 3100. Core flooding equipment consists of:

• A system of valves operated pneumatically via a computer

• An injection system, incorporating an electronically-controlled Quizix pump

• 12-inch core holder (1.5-inch diameter)

• 3 accumulators (1000 ml volume)

• Backpressure regulator

*DOI: http://dx.doi.org/10.5772/intechopen.92101*

**Length (cm)**

**Diameter (cm)**

**Core ID**

*1*

**Table 2.**

Buff Berea

**Table 3.**

*Not determine.*

*Buff Berea core properties.*

**2.2 Core flooding procedure**

*Buff Berea core X-ray diffraction (XRD) data.*

*Aggregation of Partially Hydrophilic Silica Nanoparticles in Porous Media: Quantitative… DOI: http://dx.doi.org/10.5772/intechopen.92101*

