# Evaluation of Novel Preformed Particle Gel System for Conformance Control in Mature Oil Reservoirs
## 4 Materials and Methods
### Methodology  
Chemical structure: Fourier-transform infrared spectroscopy (FTIR) using Perkin Elmer Spectrum was recorded for the CMC and CMC/PAMBA in the wave number range of 500-4000 cm\({}^{-1}\) to confirm the grafting copolymerization and formation of PPGs. Morphology: The morphological structures of both dried and swollen CMC/PAMBA in brine were visualized using scanning electron microscopy (SEM). Prior to SEM analysis, the PPG underwent three freeze-drying stages for 48 h using the Laboconco FreeZone 12 machine. The freeze-drying stages comprised (1) placing the PPG samples in the freeze-dryer chamber, chilling to \(-\)50 \({}^{\circ}\)C at a rate of 0.6 \({}^{\circ}\)C/min, and maintaining an isothermal plateau for 2 h; (2) subjecting the samples to a sublimation stage at \(-\)15 \({}^{\circ}\)C under a total gas pressure of 18 Pa; and (3) drying the samples at a higher shelf temperature of 25 \({}^{\circ}\)C under a pressure of 10 Pa to achieve optimal residual moisture content. Subsequently, SEM analysis was conducted using an FEI Nova Nano SEM 450 microscope. ImageJ software (1.54) was employed for measuring the pore sizes. Swelling behavior: Understanding the swelling behavior of the gel is essential for field applications to optimize the injection mode and design the proper particle size for plugging the targeted zone. The swelling kinetics of the CMC/PAMBA PPG were evaluated by mixing a dry PPG sample of known volume in different brine samples and recording the change in volume with time. Typically, 1 mL of dry PPG is immersed in a 50 mL tube of brine, shaken, and left to swell. The swelling ratio (SR) was calculated using Equation (1) [51]. \[SR=\frac{V_{Swellled}}{V_{dry}} \tag{1}\] \begin{table}
\begin{tabular}{c c} \hline \hline
**Name** & **Chemical Structure** & **Amount (g)** \\ \hline N\({}_{N}\)/-Methylenebisacrylamide (MBA) & \\ \hline Ammonium Persulfate (APS) & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._Rheology evaluation: The elastic modulus (G\({}^{\prime}\)), often referred to as Young's modulus, is a measure of a material's stiffness or rigidity. In the context of preformed particle gels (PPGs), the elastic modulus represents the gel's ability to deform under applied stress and return to its original shape when the stress is removed. The higher the elastic modulus, the higher the gel strength. Maintaining optimal mechanical integrity, coupled with practically acceptable injectivity, is crucial for gel applications aimed at reducing excessive water production. The elastic modulus (G\({}^{\prime}\)) in Pascals (Pa) of swollen CMC/PAMBA PPG samples was acquired through dynamic oscillatory measurements using a Haake MARS III rheometer (Figure 20). To ascertain the linear viscoelastic region of the gel sample, strain sweep experiments were conducted. The measurements were performed at a 1% strain value with a 1 mm gap height between the sensor and the plate containing the PPG samples. The frequency was set to 1.00 Hz [57; 58]. Core flooding test: To evaluate the plugging efficiency of the CMC/PAMBA PPG, core flooding experiments were conducted using fractured sandstone cores. A core flooding setup was assembled (Figure 21), consisting of an ISCO pump, two accumulators for the gel sample and brine, and a Hassler-type core holder. The sandstone cores were placed in the oven at a temperature of 120 \({}^{\circ}\)C to ensure residual water was removed before they were used. They were then vacuumed for 24 h in a vacuum cell. A 2% KCl brine was used to saturate the cores for another 24 h. Porosity was calculated using the water saturation method, and initial brine permeability was calculated using [PERSON]'s law. To create the fracture model, the fully saturated sandstone core was divided into two equal parts using an electric saw. Two stainless-steel strips of the intended fracture thickness were attached to the interior of the separated core sections. The prepared fractured sandstone core was then wrapped with Teflon and inserted into the core holder.