Studies of interaction between bitumen and thermochemical fluid (TCF): Insights from experiment and molecular dynamics simulations

Thermal enhanced oil recovery generally involves injection of steam into the reservoir or insitu heat propagation to reduce the viscosity of heavy oil. However, certain shortcomings, which are associated with steam injection, have paved way for finding an alternative method for insitu heat and pressure generation such as thermochemical fluid injection. The thermochemical fluid injection method offers several potential advantages including reduced heat loss, higher heat transfer efficiency, and negligible emission of CO2 compared to conventional steam injection. In this article, a deeper understanding of the process using the molecular dynamics simulations coupled with the experiment are presented. Guided by experimental information obtained from Saturates, Aromatics, Resin and Asphaltene fractions, total acid number, and density of bitumen sample, a molecular model of bitumen was built and validated. Subsequently, supported with the thermodynamic data obtained from the thermochemical reaction vis. enthalpy (ΔH) and order of reaction (n), Molecular dynamics simulations were used to examine the bitumen-thermochemical fluid interface, and the possible molecular interactions that could be involved between the bitumen matrix components and the thermochemical fluid. The thermochemical fluid reaction could generate sufficient temperature, typically, ≈170 °C and pressure ≈1600 Psi. The reaction was first order (n = 1) with ΔH = −370 KJ/mol, and the reaction Ea ≈ 35.5 kJ mol−1. Ultimately, molecular dynamics simulations gave detailed insights into the molecular interactions that could be established at the bitumen-thermochemical fluid interface. Our results put in evidence the changes of bitumen matrix upon the injection of thermochemical fluid. Indeed, molecular dynamics results show that the insitu heat released from the thermochemical reactions induces a homogeneous texture of the bitumen matrix via disturbing the large aggregates of the heavy bitumen components such asphaltene, and resin. The formation of salt resulted in a stronger interaction of salt-acids type between the two phases, which leads to further stabilization of the water-phase inside the bitumen matrix and prevent its collapse. Furthermore, the insitu formation of N2 gas and its diffusion through bitumen matrix softens its texture and lead to disturbing of the tight interaction between the bitumen matrix components. As, the temperature increases the kinetic energy of N2 gas increases and make it more efficient to decrease its viscosity and hence its mobility. This phenomenon has also been corroborated through the thermogravimetric analysis and the scanning electron microscopy, which revealed improved thermal decomposition performance due to reactivity and/or interfacial interactions between thermochemical fluid and bitumen matrix.