An Experimental Study of Wellbore Phase Redistribution Effects in Gas Condensate Reservoirs

This paper presents a series of experiments that were carried out at Imperial College to investigate wellbore phase redistribution (WPR) phenomena. Results are being used to verify and calibrate a transient wellbore multiphase simulator that will be used to predict the onset of WPR and design operating conditions to avoid or at least minimise it. The overall objective of the experimental study was to emulate two-phase flow in a gas condensate well-reservoir system. It was firstly aimed to investigate WPR effects independent of reservoir interaction and secondly as part of a gas condensate well-reservoir system in which the multiphase flow near the wellbore and the single phase gas away from the well could be taken into account. The well was represented by a vertical tube of approximately 10.5 m in length, and gas and condensate by air and water, respectively. The reservoir was simulated with two pressurised vessels, one for water, the other for gas, feeding into the vertical tube. The effects of WPR on the isolated well were investigated by performing shut-in tests in which the bottom and top of the tube were closed off simultaneously. The reservoir impact on WPR effects was then investigated by creating steady state conditions and shutting in the vertical tube at the top to create a transient response. The resulting transient pressure data were analysed using well test interpretation methods. The steady state pressure and void fraction, measured along the tube, were used to validate GRAMP-2, a steady state wellbore modelling code based on flow regime prediction developed at Imperial College. Good agreement was obtained with simulated and experimental results.