Modeling of molecular interactions in the system of Methane-C5+ for predicting retrograd condensation in the development of oil and gas deposits

Retrograde condensation is a critical process in the exploitation of gas condensate fields, leading to significant reductions in hydrocarbon production. This study examines the mechanisms behind this phenomenon, focusing on the BT6 ¹ reservoir of the North-Chaselsky field. Here, condensation occurs when the reservoir pressure falls to 27,64 MPa, which is only 0.12 MPa above the current pressure of 27,52 MPa.The aim of this study is to identify molecular and thermodynamic factors causing early condensation and to propose measures for maintaining reservoir pressure to reduce hydrocarbon production losses.The paper is relevant as it clarifies the physics of intermolecular interactions during gas-liquid phase filtration in the reservoir.Using the Peng-Robinson equation of state and Lennard-Jones potential, the authors of this paper conducted an analysis of intermolecular interactions in the methane-heavy hydrocarbon (C5+) system. Also, the authors found that the formation of complexes with C5+ when pressure decreases from 25 MPa down to 10–18 MPa results in the blocking of 98,9 % of the reservoir pores. This blockage is 4 to 6 times higher than the percolation threshold (15–25 %). It explains the complete cessation of gas production at the maximum condensation pressure.The results of this work underscore the need for maintaining pressure above the dew point and managing rock wettability. This study is relevant for fields with terrigenous reservoirs, where retrograde condensation presents significant challenges to project profitability.

retrograde condensation, gas-condensate fields, Peng — Robinson equation, LennardJones potential, intermolecular interactions, percolation theory