MODELING PHASE EQUILIBRIA FOR A WATER-CO2-HYDROCARBON MIXTURE USING CPA EQUATION OF STATE IN CO2 INJECTION EOR-STORAGE PROCESSES: A COLOMBIAN CASE STUDY

JD Aristizabal and C Cundar and C Guerrero and A Aguirre and JA Pasos and I Moncayo-Riascos and M Ruiz and P Benjumea and W Agudelo and R Osorio, CT&F-CIENCIA TECNOLOGIA Y FUTURO, 14, 61-76 (2024).

DOI: 10.29047/01225383.721

Currently, it is necessary to reduce CO2 emissions into the atmosphere. The oil industry in Colombia can contribute through CO2 injection processes in depleted fields. To achieve this, it is essential to know about the physicochemical interaction of CO2with reservoir fluids. To integrate CO2, water and hydrocarbon phases, advanced models are necessary to capture the phenomenology of thermodynamic equilibrium. The CPA (Cubic-Plus-Association) equation of state adds an associative term to model the interaction of water with the hydrocarbon and CO2 phase. In this work, the CO2 injection process is thermodynamically modelled in a case study of a depleted reservoir in Colombia. There is a compositional fluid with a gradient of PVT properties in a vertical relief of 10,000 ft, at a depletion condition of 2,000 psi @ 15,374 ft and an oil-water contact (OWC) at 17,000 ft. CO2 injections between 10 and 80 mol%were conducted, and through the CPA equation of state, the swelling conditions of the crude oil, the solubility of CO2 in the formation water, and the pressurization of the system were evaluated. The associative parameters of the equation were taken from literature and estimated through molecular dynamics simulations of water- CO2-Hydrocarbon interaction. Scheme 4C_1, at CO2 injection conditions greater than 40%, predicts CO2 solubility values greater than 2000 scf/bbl compared to the other literature schemes and experimental data. Scheme 2B_2 presents inconsistencies in saturation pressure calculations at high CO2 injection contents since at 60% it reports a value of 2800 psia and at 80% a value of 2600 psia. This behavior is opposite to that reported in literature. Therefore, association schemes 4C_1 and 2B_2 presented thermodynamic problems for the calculation of properties such solubilities and saturation pressures. This thermodynamic modelling with an advanced equation of state and use of molecular dynamics simulations enabled us to simulate different CO2 injection scenarios in a compositional fluid. This type of studies is key to conduct successful CO2 injection processes focused on enhanced recovery (EOR) and CO2 storage in the porous medium in a depleted compositional reservoir in Colombia.

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