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.