Large liquid volumes build up in gas-condensate pipelines when operated at low flow rates, so limited time is available before production needs to be restored or halted to manage liquid surges on ramp-up or restart. Although gas-condensate systems are rarely operated below their notional minimum turndown rate, there are circumstances where operations at low rates are necessary. This paper describes two events where large diameter gas-condensate offshore pipelines were operated for extended time periods below their minimum turndown rate. These transient events offered a valuable opportunity to assess the performance of dynamic multiphase flow simulators for operating conditions where field data are rarely available.
Large diameter gas-condensate pipelines are rarely operated below their minimum turndown rate specified during design. However there are circumstances where operations at low flow rates are necessary, such as partial shutdown of downstream facilities, which may be planned or in response to abnormal situations.
At low flow rates, large liquid volumes are likely to build up in pipelines and limited time is available before production needs to be turned up or stopped to manage liquid surges on ramp-up or restart. This paper describes two events where large diameter two-phase (gas and condensate) and three-phase (gas, condensate and aqueous phase) offshore pipelines were operated for extended time periods below their notional minimum turndown rate. For each event, comparisons between dynamic multiphase flow simulations and field measurements are presented and analysed in detail.