Theoretical and experimental investigation of pore confinement effects in gas condensate reservoirs

Abstract

Unconventional resources play an important role to meet future energy demands. Recent advances in technology has made the production from unconventional reservoirs feasible. However, it is necessary to properly study the phase behavior and flow of fluids within these reservoirs as they are not well understood. In this thesis, the impacts of fluid confinement effects, which refers to the impact the small pore spaces and pore walls on the fluid phase behaviour due to non-negligible interactions between pore walls and fluid molecules, on the phase behaviour of gas condensate systems within real unconventional rocks, were investigated. A novel experimental procedure was designed to measure dew point pressure (Pdew) of various gas-condensate fluid mixtures within different real shale rocks. Several experiments were performed to realistically study the impacts of gas condensate fluid composition, temperature, net stress and rock type on the extent of the pore confinement effects. The trends for the impacts of confinement Pdew of single component fluids and gas condensate mixtures were analyzed and it was observed that pore confinement would increase the Pdew of gas condensate mixtures while reduced the Pdew of single component fluids. The impacts of the presence of heavier components in the gas condensate mixture was found to be significant. In line with the experimental measurements, the equation of state describing confined fluid phase behavior of gas condensate mixtures was modified by modifications in binary interaction parameters. A new correlation based on the Lennard Jones interaction potential was presented to take into account the interactions between fluid and wall molecules. The proposed correlation was tuned based on the experimental results. The error of the predictability of the correlations for core sample and the fluids not used in its development was found to be within an acceptable range. Based on the modified equation of state obtained, numerical simulations were performed to investigate the impacts of pore confinement on the performance of the unconventional reservoirs. It was noted that gas production was slightly higher using the confined fluid mode which was mainly attributed to the lower fluid viscosity due to confinement. When pressure drawdown (DP) was low, models with bulk fluid produced more condensate. However, when DP increased, models with confined fluid produced more. Considering dual porosity model, dual porosity-dual permeability model, adsorption, and diffusion did not alter these trends.