Abstract
Electric submersible pumps (ESPs) are a widely used artificial lift method used to support oil production and boost pressure. They perform excellently in liquid applications and fairly well for gassy applications if properly designed and fitted with the right components, such as a reliable gas separator and/or gas handler (GH). This paper deals with the possible failure analysis of an ESP GH, specifically the consequences of mechanical breakdown of impeller blades.
Solids, such as scale, sand and debris upstream of the ESP, can cause mechanical failures or wear of exposed parts. Impellers or augers used in rotating gas separators and gas handlers are at higher risk of damage due to their hydraulic design and frontline facing the incoming abrasive fluid. Root cause analysis based on Dismantle, Inspection and Failure Analysis (DIFA) can identify the failed component and failure mechanism such as the GH with axial type impellers. A more ductile metallurgy with higher yield-strength can be proposed as corrective action and the improvement can be confirmed through Finite Element Analysis (FEA).
Solids found during ESP DIFA are believed to be the primary trigger of gas handler impellers’ failure. The sources of solids can be several and intrinsic to well operations such as little debris remaining after workover job or corrosion byproducts coming from the casing below the ESP. Because of the impellers axial design, thin blades, limited vane support at the impeller hub, tight clearances and brittle material, it is highly possible one or a few blades broke initially with a catastrophic dominoes effect as the released metal debris can be caught between the impellers and diffusers, crushing in smaller pieces can be dragged up by the produced fluid into the upper stages. The observations suggest that all blades shattered in all the 17 GH impellers, leaving just the impellers’ hub that is attached to the shaft. Likewise, multiple dents and broken vanes can be observed in the diffusers of the GH as a result of the metal crushing. The failure mechanism can extend to the pump stages as some fragments of the GH can be dragged further up that could result in shaft overload and leading to failure of the two-piece shaft coupling between the gas handler and the pump.
This paper provides valuable insight about potential inherent design weaknesses of some gas handlers fitted with axial or helical-axial stages. The DIFA results support the proposal for an upgrade of the metallurgy as a quick fix to cope with rig operation commitments. The higher strength of upgraded GH impellers was validated through FEA; however, additional improvements mainly in terms of mechanical design are also proposed and discussed.
