Enhancing Well Interventions with the Use of Transient Software - New Case Histories from Around the World

Abstract

Abstract Since the mid-1980s, advances in coiled tubing (CT) modelling software have enhanced operational efficiency, reduced technical risks, expanded the acceptable operating envelope and improved well intervention success rates. Until relatively recently, models were the steady-state type. Since 2010 dynamic modelling for CT operations has been utilized. This paper, focusing exclusively on transient modelling, incorporates unpublished novel case histories showing pre-job optimization and post-job investigations. The focus is on showing the simulation advantages of transient versus steady-state conditions. The transient model predicts the changes over time resulting from varying pumped and produced fluid rates, varying fluid types, two-phase relationships, location of solids, location of the CT and the wellhead choke size. Equations for the conservation of mass and momentum and a unified drift-flux model, valid for all flow regimes, are included in the model. Based on experimental testing on a full-scale flow loop, a critical gas flow velocity model was developed. It has been validated against published case histories and results of other transient models primarily developed for pipeline operations. Several case histories are presented, showing phenomena that cannot be captured by steady-state CT models. First, a review of two cases of post-job investigations are presented: a re-calculation considering multiple well pressures and fluid content changes, to confirm that the CT weight was accurately recorded prior to an operational incident; and a re-calculation of a solids cleanout operation where incorrect execution resulted in stuck CT. Second, a review of two cases of pre-job analysis includes the modelling the switching of a tool with respect to time instead of pressure (required because high nitrogen rates mask surface pressure indications of downhole changes); and the modelling of a complex situation where the client requested an optimized dewatering operation with only a small volume of nitrogen available. Finally, cases of optimizing solids cleanout removal with multiple changes in fluid rheology are reviewed. Three prior papers (Salim and Li 2009; Salim et al. 2010; Li et al. 2012) regarding this transient model were focused on the model theory and gas lift optimizations. The practical cases presented in this paper are novel to CT transient modelling papers and provide operators with a greater understanding of the value that the transient modelling can provide to their operations.