Tubing corrosion is a major well integrity challenge faced during the well lifecycle. Corrosion onset conditions need to be predicted with accuracy so that preventive and corrective actions can be taken before corrosion results in a safety hazard. One of the requirements for corrosion onset is the accumulation of free water along the wellbore. Given the transient nature of multiphase flow inside the wellbore, a transient multiphase simulator is required to accurately predict water accumulation inside the wellbore.
A comprehensive multiphase transient simulator has been used to evaluate the conditions that would allow or prevent water droplets in emulsion to wet the tubing and create corrosive conditions for two candidate wells; whereas a laboratory study indicated a stable emulsion with water dispersed in oil, hence pointing to no tubing wetting, field inspections showed severe corrosion. The aim of the study is to virtually recreate the field conditions by tuning different model parameters. Flow regime and emulsion analysis were done for the candidate wells to understand the likelihood of corrosion in the tubing. Further, sensitivities were performed for parameters such as tubing diameter, water cut, flow rate, and tubing roughness.
The model predictions for the first well (a dual-string well) indicated that both strings experience stratified flow until the bubblepoint, with the presence of free water near the tubing wall indicating the likelihood of corrosion. For the second well, which is a horizontal well with inflow control devices (ICDs), simulations indicated that emulsion was formed inside the ICD orifice, but the water phase still touched wall surface. Once the fluid entered the tubing, the flow regime was stratified, with water touching the wall, thus enabling the conditions ripe for onset of corrosion.
This study underscores the role of transient simulations in predicting the flow regime and emulsion formation in multiphase flow inside wellbores and thereby providing valuable information for assessing the likelihood of corrosion inside the wellbore.