Innovative Use of Transient Flow Modelling for Successful Planning and Execution of Complex High Pressure (HHP) Well Unloading: Plan and Results

Unloading wells post drilling and completion is critical in ensuring risk of well productivity impairment due to extended residence of drilling and completion fluids in the well is minimized. In addition, unloading high pressure (HHP) gas wells can be quite complex since it includes rapid changes in operating conditions (pressure, temperatures and rates), which if not planned properly, can lead to exceeding design operating envelopes and in the worst-case result in process safety incidents. The objective of this paper is to present a case study, which demonstrates the application of transient flow modelling for analysis of complex high pressure (HHP) gas well unloading. Traditional well and surface network modelling tools and softwares use steady state flow models. However, well unloading is a transient phenomenon with rapid changes in pressure, temperature, flowrate and hold-up and ideally requires multiphase transient flow modelling software to predict the conditions accurately. This paper describes how transient flow simulation, using the software package OLGA, was applied to model well unloading with the objective to keep the flow within the operating envelope of the well and surface equipment. The execution was carried out safely and successfully aided by the modelling work carried out in OLGA. A comparison of the modelled and actual measured parameters is presented showcasing the utility of transient flow modelling in planning, decision making and smooth execution. The model was used to optimize the choke positions within the constraints of low temperature limit, while avoiding the requirement of heat exchangers, steam generators and flare stack and avoid a long learning curve during execution. This also ensured that flaring was not required which means no Greenhouse Gas (GHG) emissions and the produced hydrocarbons were monetized.