Profile of critical rate for 106 vertical wells producing from high pressure formations has been used to determine an unloading critical rate for well producing gas and condensate. The evaluation involved loaded, questionable and unloaded wells. When this data was compared with experimental data obtained from flow loop where liquid loading condition was investigated, it was observed that any gas condensate well producing above a critical rate of 12 MMSCF/D will produce in an unloading manner.
OLGA, a 3-phase transient multiphase flow simulator was used to confirm the conclusion of well test result. Four gas condensate wells were investigated out of 106 well tested at field conditions - one unloaded; one questionable and two loaded. Results of the simulation confirmed the ‘unloaded’ well was actually producing freely in a stable manner at the wellhead. The ‘questionable’ well was found to be to be producing in churn flow regime characterized by certain degree of instability. The two ‘loaded wells’, on the other hand, were found to be producing but characterized with mild and severe flow instability at the wellhead. A loaded well simulated with 12 MMSCF/D production rate produced in a stable manner.
Three of the wells selected for study had production tubing depth greater than 10,000ft. to study effect of flow development length on liquid loading behaviour of gas condensate well. A modified Froude number based on production tubing depth and entrained liquid fraction in the gas stream showed that a gas condensate is most likely to be loaded if operated below a value of 1000.