Turbomachinery is vital to exploiting deepwater wells

The 40^th Turbomachinery Symposium is taking place this week in Houston, Texas. They keynote was delivered by Joe Gregory, General Manager of Major Capital Projects within Chevon’s Deepwater Exploration and Projects Business Unit. He discussed the technology needs of for deepwater drilling in the Gulf of Mexico. His company is working on the development of fields in the Miocene and Lower Tertiary strata at depths of 7000 feet and beyond – in some cases as much as 16,000 feet.

“Specialists in pumps and turbomachinery are critical to overcoming vast obstacles in developing these fields,” said Gregory.

Chevron is testing Electrical Submersible Pumps (ESP) with a view to deploying them to improve oil recovery. As well as seafloor pumps in deep water, the company sees value in placing ESPs down the well  as they have greater drawdown potential.

“We are moving these pumps from the qualification into the execution phase,” said Gregory.

After the keynotes, the technical sessions began. Cory Zorzi, Technical Improvement Leader at the Elliott Group discussed a root cause failure analysis for recurring impeller failures in a 4.7 mtpa LNG propane compressor in three trains being driven by Frame 7s used by RasGas. Investigation looked into the causes of high cycle fatigue (HCF). This found mistuning of blades leading to problematic frequencies due to vane wake interaction.

To address this, Elliott resculpted the leading edge of the compressor blades, relocated a weld to reduce stress and changed the impeller to more durable material. In addition, the scrubber mist eliminators were upgraded, the machine was uprated to minimize choke  operation and the inlet was changed from 14 to 6 vanes to provide better flow uniformity.

“Mistuned or disk modal excitation from upstream vane wakes may be exacerbated through vane aggravation from entrained liquid and/or prolonged choke flow,” said Zorzi. “Both must be avoided.”