Sand management and erosion prediction in subsea multiphase pumps

Over the past ten years, subsea multiphase pumping has accomplished extraordinary technology breakthroughs. The drivers are the oil and gas companies’ requirements for deeper and more remote subsea production satellites along with producing more challenging fluids. The multiphase pump (MPP) technology has kept evolving, breaking records in terms of shaft power, design pressure, differential pressure, and high viscosity capabilities. In addition, the current reliability data shows 86.5% probability of 5 years failure-free operation. Today, a main challenge is the ability to withstand sand erosion. A subsea MPP is placed on the seafloor to increase the production from subsea oil and gas wells, normally without any upstream separator or sand control system. The inevitable sand production is directed through the pump and transported further to the topside arrival separator. The MPP considered in this paper is a dynamic helico-axial pump with rotational speeds typically ranging up to 4,600 rpm and 3.5 MW. Obviously, both pump vendor and operator have made significant efforts to make the MPP as robust as possible. The first part of this paper describes how sand production is mitigated and controlled in a subsea oil and gas production system, but also how an accidental sand event can nevertheless happen. In the second part, the various wear mechanisms of MPP components are explained based on operational experience and wear tests. Finally, it presents the comparison of the wear observed on the Moho pump retrieved from the field with the wear rate and pattern predicted by the in-house MPP wear prediction model.