Gas-Condensate Flow in Perforated Regions

Abstract

Abstract The most crucial region affecting well productivity is the perforated region. Considerable effort has been directed to study this subject, mathematically by many investigators, but they are mainly focused on single-phase flow with limited information on the two-phase flow systems. It has been demonstrated, first by this laboratory and subsequently by other researchers, that the gas and condensate relative permeability (kr) can increase significantly by increasing the flow rate, contrary to the common understanding. This effect, known as positive coupling, complicates the flow of gas and condensate near the wellbore even further when it competes with inertial forces at higher velocities typical of those around perforation tips. The flow of gas and condensate in perforated regions was studied in this work using a finite-element modelling approach. The model allows for changes in fluid properties and accounts for the positive coupling and negative inertial effects using a fractional flow based relative permeability correlation. A sensitivity analysis on the impact of perforation characteristics such as density, phasing, length and radius as well as that of fluid properties, rock characteristics, wellbore radius, fractional flow and rate on well productivity was conducted resulting in some valuable practical guidelines for optimum perforation design. The results were expressed in terms of the productivity ratio, PR, defined as the ratio of the total flow rate of gas and condensate in the perforated completion to that of an unperforated open-hole for the same pressure drop. The results indicated that PR is independent of fluid properties, fractional flow and rates for most practical purposes.