Evaluation of polymer-calcite interfacial strength through a uniaxial tensile simulation study Keat Yung Hue 1 , Myo T. M. Maung 2 , Omar K. Matar 1 , Paul F. Luckham 1 , Erich A. Müller 1* 1 Imperial College London, United Kingdom 2 PETRONAS Research Sdn. Malaysia In energy applications, when the carbonate rock is weak and poorly consolidated, the hydrocarbon extraction process produces undesired particles which will impact on hydrocarbon productivity and increase environmental waste. Solids production control is essential to mitigate the problem. The solids production risk can be reduced by theinjection of formation-strengthening chemicals into the formation. In this research, molecular dynamics (MD) simulation was employed to screen different polymer candidates. This can be evaluated from the stress-strain response and the adhesion properties from a surrogate polymer-calcite uniaxial tensile simulation study. Classical atomistic MD simulations and pcff+ forcefield were employed to model the interaction of the polymer with the calcite (1 0 4). Polyacrylamide-based polymers were selected as potential candidates, including pure polyacrylamide (PAM), hydrolysed polyacrylamide (HPAM 33%) and sulfonated polyacrylamide (SPAM 33%) while polyethylene (PE) was modelled as control case. For each separate case, the polymer matrix was filled between the upper and lower solids surface layer, each consisted of 3 calcite layers. The polymer was allowed to move freely as deformable region, where the upper layer was pulled upward in z -direction and the polymer deformed slowly. The stress-strain response was measured from the normal force acting on the calcite lower layer normalized by the surface area, and the polymer strength properties were analysed. In a separate simulation, the polymer matrix was frozen, and the stress-strain behaviour was measured with both the polymer and calcite upper layer detached from the lower calcite surface completely. The stress-strain response behaviour is depicted in Figure 1 , while the polymer deformation behaviour can be observed in the simulation snapshot in Figure 2 . For the deformable polymer cases, in general, when the calcite upper layer is pulled upward, the polymer reaches peak tensile stress and decreases drastically due to the damage in the polymer matrix. Preliminary studies shows that the peak stress value recorded for the polymer- calcite system is the same as pure polymer system, which suggests the value is attributed to pure polymer tensile strength. Hence, the frozen polymer cases are modelled to force the detachment of the polymer from the interface, where the tensile stress recorded is considered as interfacial strength from literature[1]. The maximum tensile stress in Figure 1 shows that polymer-calcite interfacial strength is significantly stronger than pure bulk polymer strength, validating the polymers can adsorb strongly to the calcite. As shown in Figure 2 , HPAM33% shows better polymer strength due to the presence of carboxylate group in ionized form, which agrees with literature[2]. Uniaxial tensile simulation studies allow the interpretation of the polymer deformation mechanisms and provide insights into the polymer-calcite interfacial strength analysis. It serves as a useful screening simulation tool to evaluate the suitable potential candidates for improved adsorption and formation strengthening performance.
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