**2.2 Core flooding procedure**

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:


**Figure 4** shows the schematic of core flooding equipment.

After brine injection, 5 pore volumes of 0.05% SiO2 NPN-ST was injected into Buff Berea core at 0.5 ml/min and aged for 24 hours. The core was flooded with brine for 10 pore volumes at 0.5 ml/min or until stable pressure drops is obtained. Finally, core is subjected to 2 pore volumes of brine at 0.5, 1.0 and 1.5 ml/min to determine the final permeability to water. The effluent during NPN-ST and brine post flush injection were collected every 5 ml per tube and analyzed for particle size using light scattering method. After completion of core flooding test, each of the treated Buff Berea cores were dried and cut into three sections (inlet, middle and outlet) for Field Scanning Electron Microscope (FESEM) analysis. The attachment and aggregation of silica nanoparticles under FESEM were determined by comparing the photomicrographs of untreated core (obtained from same core cut with treated cores).

**Figure 4.** *Schematic of core flooding equipment.*

**245**

**2.3 Micromodel test**

*Micromodel pore and grain size.*

**Table 4.**

**Figure 6.**

each ROI was analyzed.

**3.1 Core flooding test**

**3. Results and discussion**

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

**Figure 5** illustrates the micromodel experimental set up that comprised of 3 main components; the injection port and lines, that include the differential pressure set up (bypassed for this study), a flow cell represents as porous network (45 mm × 15 mm dimension) with 2.5 Darcy permeability that made of borosilicate glass and the slide made of polypropylene. The flow cell is placed under NIS-Element AR microscope which has 2X, 4X, 8X and 20X zoom lenses connected to a computer for image viewing. Six region of interest (ROI) have been identified at inlet, middle and outlet site of the micromodel. The images were taken by using microscope at 2X resolution. **Figure 6** shows the ROIs used for this micromodel experiment. The pore and grain size of micromodel is categorized as fine, medium and coarse. The pore and grain size output indicate the overall ROIs studies. **Table 4** shows the micromodel pore and grain size determined by using Annotations and Measurement tool on microscope software. 30 ml of 0.05% NPN-ST was injected at 0.001 ml/min followed by 40 ml of 1.5 wt% brine at 0.1 ml/min into the glass micromodel and aged for 1 week. After 1 week, 30 ml of brine was injected and the micromodel image of

**Properties Fine Medium Coarse** Pore size (μm) 36.33–87.76 90.3–191.4 205.37–441.46 Grain size (μm) 110.27–186.08 209.82–305.02 387.13–705.90

*Region of interest (ROI) at inlet, middle and outlet of the micromodel porous network.*

For this study, 0.05% NPN-ST concentration was selected based on gravityassisted flow (GAF) reported in previous work [29]. Injection rate was fixed at

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

**Figure 5.** *Schematic of micromodel system.*

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

#### **Figure 6.**

*Nano- and Microencapsulation - Techniques and Applications*

**Figure 4** shows the schematic of core flooding equipment.

After brine injection, 5 pore volumes of 0.05% SiO2 NPN-ST was injected into Buff Berea core at 0.5 ml/min and aged for 24 hours. The core was flooded with brine for 10 pore volumes at 0.5 ml/min or until stable pressure drops is obtained. Finally, core is subjected to 2 pore volumes of brine at 0.5, 1.0 and 1.5 ml/min to determine the final permeability to water. The effluent during NPN-ST and brine post flush injection were collected every 5 ml per tube and analyzed for particle size using light scattering method. After completion of core flooding test, each of the treated Buff Berea cores were dried and cut into three sections (inlet, middle and outlet) for Field Scanning Electron Microscope (FESEM) analysis. The attachment and aggregation of silica nanoparticles under FESEM were determined by comparing the photomicrographs of untreated core (obtained from same core cut with treated cores).

• Automated auto sampler

• A balance to a data logger

**244**

**Figure 5.**

*Schematic of micromodel system.*

**Figure 4.**

*Schematic of core flooding equipment.*

*Region of interest (ROI) at inlet, middle and outlet of the micromodel porous network.*


#### **Table 4.**

*Micromodel pore and grain size.*

#### **2.3 Micromodel test**

**Figure 5** illustrates the micromodel experimental set up that comprised of 3 main components; the injection port and lines, that include the differential pressure set up (bypassed for this study), a flow cell represents as porous network (45 mm × 15 mm dimension) with 2.5 Darcy permeability that made of borosilicate glass and the slide made of polypropylene. The flow cell is placed under NIS-Element AR microscope which has 2X, 4X, 8X and 20X zoom lenses connected to a computer for image viewing. Six region of interest (ROI) have been identified at inlet, middle and outlet site of the micromodel. The images were taken by using microscope at 2X resolution.

**Figure 6** shows the ROIs used for this micromodel experiment. The pore and grain size of micromodel is categorized as fine, medium and coarse. The pore and grain size output indicate the overall ROIs studies. **Table 4** shows the micromodel pore and grain size determined by using Annotations and Measurement tool on microscope software. 30 ml of 0.05% NPN-ST was injected at 0.001 ml/min followed by 40 ml of 1.5 wt% brine at 0.1 ml/min into the glass micromodel and aged for 1 week. After 1 week, 30 ml of brine was injected and the micromodel image of each ROI was analyzed.

#### **3. Results and discussion**

#### **3.1 Core flooding test**

For this study, 0.05% NPN-ST concentration was selected based on gravityassisted flow (GAF) reported in previous work [29]. Injection rate was fixed at

0.5 ml/min throughout the injection to eliminate the permeability impairment caused by nanoparticles injection at high rates [27]. The recorded pressure drops during initial brine, NPN-ST and brine post flush injection enable the interpretation of silica nanoparticles adsorption or plugging inside the porous media. **Figure 7** shows the pressure drop profiles of water wet Buff Berea core; B1–10, B3–21 and L1 when injected with 0.05% NPN-ST at 30°C. B1–10 core flood results showed rapid increased in pressure drops from ~0.28 psi to maximum ~1.09 psi after 2.6 pore volumes of NPN-ST injection. The rapid increased of pressure drops at initial stage of silica nanoparticles injection caused by multilayer adsorption and gradual straining effects [17, 18]. After 2.6 pore volumes, the pressure drops gradually declined to ~0.87 psi that indicates the adsorption process had completed. The pressure drops start to increase rapidly to maximum ~1.16 psi during brine post flush which confirmed the NPN-ST multilayers adsorption. The pressure drops gradually declined after 2.4 pore volumes brine post flush and stabilized and reached steady state at 0.37 psi after six pore volumes that indicate no further detachment and straining of NPN-ST.

B3–21 and L1 core generated slightly higher pressure drops at initial stage and during post flush but with similar trend with B1–10 core. The pressure drops of L1 core increased rapidly from ~0.5 psi to maximum ~2.3 psi. After 1.56 pore volumes of NPN-ST injection, the pressure drops declined and stabilized at ~1.9 psi and further declined during brine post flush and stabilized at ~0.77 psi. Multilayer adsorption and gradual straining effects of B3–21 generated the highest pressure drops from ~0.27 to maximum 3.11 psi compared to B1–10 and L1 core. Nevertheless, B3–21 reached steady state at 0.4 psi, which slightly higher compared to B1–10 core. **Figure 8** shows the pressure drop profiles of Buff Berea core B7–16 and L2 when injected with 0.05% NPC-ST at 60°C. After brine injection, sharp increase in pressure drop from ~0.20–0.24 psi to maximum ~ 0.9–1.53 psi was observed. After 2.7 pore volumes of NPC-ST injection, the pressure drop temporary decline until sharp increase in pressure drop to maximum value of 82.61 and 26.61 psi for B7–16 and L2 core respectively. The maximum pressure drops observation occurred for less than 1 pore of NPN-ST injection until the pressure drop gradually declined and stabilized at ~ 0.28–0.30 psi. Pressure drop at 60°C showed more rapid increasing in pressure

#### **Figure 7.**

*Pressure drops of buff Berea Core B1–10, B3–21 and L1 during (I) initial brine injection, (II) 0.05% NPN-ST injection and (III) brine post flush at 30°C.*

**247**

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

drops in comparison with 30°C during NPC-ST injection, but the permeability

*/sec*), *µ* (*cP*), *L* (*cm*), *A* (*cm2*

each treated cores were calculated using the following equation:

**3.2 Field scanning electron microscope (FESEM) analysis**

flow rate, water viscosity, core length, core area and pressure drops respectively.

The permeability before and after silica nanoparticles injection were calculated using the pressure drops data during brine injection and calculated using

*Pressure drops of buff Berea Core B7–16 and L2 (I) initial brine injection, (II) 0.05% NPN-ST injection and* 

*QL*

**Table 4** shows the calculated permeability impairment of Buff Berea core B1–10, B3–21, L1, B7–16 and L2 after NPN-ST injection. The permeability impairment of

where *kimp*, *kwi* and *kwf* is permeability impairment, initial permeability and final

The calculated permeability impairment for B1–10, B3–21, L1, B7–16 and L2 are 28.6, 30.3 and 26.2% for 30°C and 19.6 and 16.4% at 60°C respectively as shown in **Table 5**. The permeability impairment between cores at designated temperature showed close values and slightly lower compared with other silica nanoparticles investigated in previous study [25–27]. Permeability impairment at 60°C is lower compared to 30°C indicated the silica nanoparticles used in this study is suitable for

FESEM photomicrographs of untreated core and cores injected with NPN-ST were compared to confirm the silica nanoparticles adsorption on core surface. At 500 nm magnification, untreated core displays as uniform surface as shown in **Figure 9**. Spherical shape of silica nanoparticles were detected on surface of B3–21

*<sup>A</sup><sup>P</sup>* (1)

\_ (*kwi* − *kwf*) *kwi*

) and *ΔP* (*atm*) is permeability,

]*x* 100% (2)

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

impairment is slightly lower at 60°C.

where *k* (*D*), *Q* (*cm3*

*(III) brine post flush at 60°C.*

permeability respectively.

high temperature application.

*<sup>k</sup>* = \_

*Permeability impairment*, *kimp* = [

Darcy's law.

**Figure 8.**

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

#### **Figure 8.**

*Nano- and Microencapsulation - Techniques and Applications*

0.5 ml/min throughout the injection to eliminate the permeability impairment caused by nanoparticles injection at high rates [27]. The recorded pressure drops during initial brine, NPN-ST and brine post flush injection enable the interpretation of silica nanoparticles adsorption or plugging inside the porous media. **Figure 7** shows the pressure drop profiles of water wet Buff Berea core; B1–10, B3–21 and L1 when injected with 0.05% NPN-ST at 30°C. B1–10 core flood results showed rapid increased in pressure drops from ~0.28 psi to maximum ~1.09 psi after 2.6 pore volumes of NPN-ST injection. The rapid increased of pressure drops at initial stage of silica nanoparticles injection caused by multilayer adsorption and gradual straining effects [17, 18]. After 2.6 pore volumes, the pressure drops gradually declined to ~0.87 psi that indicates the adsorption process had completed. The pressure drops start to increase rapidly to maximum ~1.16 psi during brine post flush which confirmed the NPN-ST multilayers adsorption. The pressure drops gradually declined after 2.4 pore volumes brine post flush and stabilized and reached steady state at 0.37 psi after six pore volumes that indicate no further detachment and straining of

B3–21 and L1 core generated slightly higher pressure drops at initial stage and during post flush but with similar trend with B1–10 core. The pressure drops of L1 core increased rapidly from ~0.5 psi to maximum ~2.3 psi. After 1.56 pore volumes of NPN-ST injection, the pressure drops declined and stabilized at ~1.9 psi and further declined during brine post flush and stabilized at ~0.77 psi. Multilayer adsorption and gradual straining effects of B3–21 generated the highest pressure drops from ~0.27 to maximum 3.11 psi compared to B1–10 and L1 core. Nevertheless, B3–21 reached steady state at 0.4 psi, which slightly higher compared to B1–10 core. **Figure 8** shows the pressure drop profiles of Buff Berea core B7–16 and L2 when injected with 0.05% NPC-ST at 60°C. After brine injection, sharp increase in pressure drop from ~0.20–0.24 psi to maximum ~ 0.9–1.53 psi was observed. After 2.7 pore volumes of NPC-ST injection, the pressure drop temporary decline until sharp increase in pressure drop to maximum value of 82.61 and 26.61 psi for B7–16 and L2 core respectively. The maximum pressure drops observation occurred for less than 1 pore of NPN-ST injection until the pressure drop gradually declined and stabilized at ~ 0.28–0.30 psi. Pressure drop at 60°C showed more rapid increasing in pressure

*Pressure drops of buff Berea Core B1–10, B3–21 and L1 during (I) initial brine injection, (II) 0.05% NPN-ST* 

**246**

**Figure 7.**

*injection and (III) brine post flush at 30°C.*

NPN-ST.

*Pressure drops of buff Berea Core B7–16 and L2 (I) initial brine injection, (II) 0.05% NPN-ST injection and (III) brine post flush at 60°C.*

drops in comparison with 30°C during NPC-ST injection, but the permeability impairment is slightly lower at 60°C.

The permeability before and after silica nanoparticles injection were calculated using the pressure drops data during brine injection and calculated using Darcy's law. *<sup>k</sup>* = \_

$$k = \frac{Q\mu L}{A\Delta P} \tag{1}$$

where *k* (*D*), *Q* (*cm3 /sec*), *µ* (*cP*), *L* (*cm*), *A* (*cm2* ) and *ΔP* (*atm*) is permeability, flow rate, water viscosity, core length, core area and pressure drops respectively.

**Table 4** shows the calculated permeability impairment of Buff Berea core B1–10, B3–21, L1, B7–16 and L2 after NPN-ST injection. The permeability impairment of each treated cores were calculated using the following equation: \_

$$\text{Permeability impairment}, k\_{imp} = \left[\frac{(kw\_l - kw\_f)}{kw\_l}\right] \propto 100\% \tag{2}$$

where *kimp*, *kwi* and *kwf* is permeability impairment, initial permeability and final permeability respectively.

The calculated permeability impairment for B1–10, B3–21, L1, B7–16 and L2 are 28.6, 30.3 and 26.2% for 30°C and 19.6 and 16.4% at 60°C respectively as shown in **Table 5**. The permeability impairment between cores at designated temperature showed close values and slightly lower compared with other silica nanoparticles investigated in previous study [25–27]. Permeability impairment at 60°C is lower compared to 30°C indicated the silica nanoparticles used in this study is suitable for high temperature application.

#### **3.2 Field scanning electron microscope (FESEM) analysis**

FESEM photomicrographs of untreated core and cores injected with NPN-ST were compared to confirm the silica nanoparticles adsorption on core surface. At 500 nm magnification, untreated core displays as uniform surface as shown in **Figure 9**. Spherical shape of silica nanoparticles were detected on surface of B3–21


#### **Table 5.**

*Permeability impairment of buff Berea core B1–10, B3–21, L1, B7–16 and L2.*

**249**

**3.4 Micromodel test**

sured according to fine, medium and coarse.

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

measured effluent particle size during NPN-ST is smaller compared to brine post flush as shown in blue line in **Figures 15**–**17**. Most of silica nanoparticles aggregates were flushed out, while the majority of larger particles size was detected during brine post flush as shown in orange line in **Figures 15**–**17**. The measurement of particles size provides useful information for this experimental work where the larger particles size corresponds with high pressure drops and vice-versa.

The qualitative method using glass micromodel flooding test allow the in-situ visualization during silica nanoparticles injection and brine injection that enable the image capture for aggregation analysis. The micromodel porous network before fluid injection is shown **Figure 18**. Silica nanoparticles particles propagate in the porous media that captured at the respective ROIs marked in red circle as shown in **Figure 19**. Gelled liked suspension was observed in the porous network when the silica nanoparticles in contact with brine that indicate aggregation marked in red arrow as shown in **Figure 20**. The size of aggregation at respective ROIs was mea-

The aggregation phenomena associated with the sharp increase in pressure drops

observed during core flooding test when silica nanoparticles injected into water

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

*FESEM photomicrographs of buff Berea core B1–10 treated with NPN-ST.*

*FESEM photomicrographs of buff Berea core L1 treated with NPN-ST.*

*FESEM photomicrographs of buff Berea core B7–16 treated with NPN-ST.*

**Figure 10.**

**Figure 11.**

**Figure 12.**

#### **Figure 9.**

*FESEM photomicrographs of untreated buff Berea core at 500 nm magnification.*

core with average particle size between 30 and 36 nm. Some aggregation of silica nanoparticles was observed at the inlet and middle core section and can be consider as minimal aggregation. Clear image of spherical silica nanoparticles adsorbed on the surface of L1 core observed at the inlet, middle and outlet section which also consider minimal aggregation. For both B1–10 and L1 core, most of the spherical particles was observed at the outlet section of the core where the non-adsorb silica nanoparticles was flushed out during post brine injection. **Figures 10** and **11** shows the FESEM photomicrographs at inlet, middle and outlet section of B1–10 and L1 core at 500 nm magnification.

On the other hand, no clear silica nanoparticles image detected for B7–16 and L2 core at inlet and middle section. Most of the spherical shape which also formed as aggregates observed at the outlet core section but the high charging during FESEM analysis caused unclear photomicrographs image as shown in **Figures 12** and **13**. Further analysis of aggregation of silica nanoparticles inside the porous media showed the aggregation could be substantial when in contact with residual water in the core. High aggregation can cause serious pore plugging and ultimately reduce the permeability. The silica nanoparticles spherical shape attached with each other and formed aggregates as shown in **Figure 14**.
