**3.3 Particle size of core flood effluents**

The particles size of silica nanoparticles and post flush effluents provide indirect relationship with silica nanoparticles aggregation in the porous media. The

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

**Figure 10.**

*Nano- and Microencapsulation - Techniques and Applications*

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

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

**Initial core permeability,** *kwi* **(mD)**

B1–10 30 247.8 176.8 28.6 B3–21 30 229.3 159.9 30.3 L1 30 234.8 173.3 26.2 B7–16 60 193.9 155.9 19.6 L2 60 253.5 211.9 16.4

**Final core permeability,** *kwf* **(mD)**

**Permeability impairment,** *kimp* **(%)**

**Test temperature (°C)**

**Core ID**

**Table 5.**

**Figure 9.**

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

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

The particles size of silica nanoparticles and post flush effluents provide indirect relationship with silica nanoparticles aggregation in the porous media. The

**248**

core at 500 nm magnification.

and formed aggregates as shown in **Figure 14**.

**3.3 Particle size of core flood effluents**

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

**Figure 11.**

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

**Figure 12.**

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

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.

#### **3.4 Micromodel test**

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 measured according to fine, medium and coarse.

The aggregation phenomena associated with the sharp increase in pressure drops observed during core flooding test when silica nanoparticles injected into water

**Figure 13.**

*FESEM photomicrographs of buff Berea core L2 treated with NPN-ST.*

#### **Figure 14.**

*FESEM photomicrographs of silica nanoparticles aggregation in the outlet section of buff Berea core.*

#### **Figure 15.**

*B3–21 core effluent particles size during NPN-ST injection and brine post flush.*

wet Buff Berea core. The treated micromodel was aged for 1 week to investigate the degree of aggregation. Post brine injection flushed out some of the silica nanoparticles suspension as shown in **Figure 21**. The size of aggregation size at respective ROIs was measured to compare with the initial stage of brine injection. The reduction of gelled-size aggregates results corresponds with the declined in pressure drops during brine post flush injection. Gel-liked suspension remains adsorbed in some parts of the porous network and strained on the pore walls. In relation, during

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**Figure 16.**

**Figure 17.**

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

core flooding test, silica nanoparticles adsorption and straining will reduce the core

Overall the aggregation size is reduced during brine post flush but some part formed bigger aggregates that possibly occurred when brine keep in contact with nanoparticles blocked in the porous network. Significant aggregates appeared after 1st and 2nd stage of brine injection at specified ROIs (ROI 1, ROI 2, ROI 3, ROI 4, ROI 5 and ROI 6), classified into fine, medium and coarse aggregation size. At initial stage, fine aggregates size during 1st and 2nd brine injection at each ROIs was not significant from one another. Since their size are relatively small, they are found abundantly in suspension mode (unattached to wall) which prone to propagate in the porous network. Medium aggregates size during 1st and 2nd brine injection indicate size reduction from the front (ROI 1/ROI 4) to end (ROI 3/ROI 4). After a week, the aggregates size at each ROIs decreased at about 5% and below. The medium size range during 1st and 2nd brine injection was insignificant which fall between 100 and 170 μm and 60–180 μm. Coarse aggregates size during 1st and 2nd

The size of aggregation during initial brine and post flush is shown in **Figure 22**.

permeability and block the fluid pathways.

*L2 core effluent particles size during NPN-ST injection and brine post flush.*

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

*L1 core effluent particles size during NPN-ST injection and brine post flush.*

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

**Figure 16.** *L1 core effluent particles size during NPN-ST injection and brine post flush.*

**Figure 17.**

*Nano- and Microencapsulation - Techniques and Applications*

*FESEM photomicrographs of buff Berea core L2 treated with NPN-ST.*

wet Buff Berea core. The treated micromodel was aged for 1 week to investigate the degree of aggregation. Post brine injection flushed out some of the silica nanoparticles suspension as shown in **Figure 21**. The size of aggregation size at respective ROIs was measured to compare with the initial stage of brine injection. The reduction of gelled-size aggregates results corresponds with the declined in pressure drops during brine post flush injection. Gel-liked suspension remains adsorbed in some parts of the porous network and strained on the pore walls. In relation, during

*B3–21 core effluent particles size during NPN-ST injection and brine post flush.*

*FESEM photomicrographs of silica nanoparticles aggregation in the outlet section of buff Berea core.*

**250**

**Figure 15.**

**Figure 13.**

**Figure 14.**

*L2 core effluent particles size during NPN-ST injection and brine post flush.*

core flooding test, silica nanoparticles adsorption and straining will reduce the core permeability and block the fluid pathways.

The size of aggregation during initial brine and post flush is shown in **Figure 22**. Overall the aggregation size is reduced during brine post flush but some part formed bigger aggregates that possibly occurred when brine keep in contact with nanoparticles blocked in the porous network. Significant aggregates appeared after 1st and 2nd stage of brine injection at specified ROIs (ROI 1, ROI 2, ROI 3, ROI 4, ROI 5 and ROI 6), classified into fine, medium and coarse aggregation size. At initial stage, fine aggregates size during 1st and 2nd brine injection at each ROIs was not significant from one another. Since their size are relatively small, they are found abundantly in suspension mode (unattached to wall) which prone to propagate in the porous network. Medium aggregates size during 1st and 2nd brine injection indicate size reduction from the front (ROI 1/ROI 4) to end (ROI 3/ROI 4). After a week, the aggregates size at each ROIs decreased at about 5% and below. The medium size range during 1st and 2nd brine injection was insignificant which fall between 100 and 170 μm and 60–180 μm. Coarse aggregates size during 1st and 2nd

**Figure 18.** *Micromodel porous network before fluid injection.*

#### **Figure 19.**

*Micromodel porous network during silica nanoparticles injection. Silica nanoparticles flowed through porous media marked in red circle at ROI 1, ROI 2, ROI 3, ROI 4, ROI 5 and ROI 6.*

brine injection indicate size reduction from the front (ROI 1/ ROI 4) to end (ROI 3/ ROI6). After one week aging, the aggregates size decreased at about 10% and below at ROI 3/ROI 5 for 1st brine injection, then decreased at ROI 1, ROI 3 and ROI 5 for 2nd brine injection. The coarse size range during 1st/2nd brine injection are significant which fall between 190 and 340 μm and 160–430 μm.
