Investigations of Flow Behavior Formation in Well-Head Jumpers During Restart with Gas and Liquid
Authors: Coletta Angelina , Volk Michael , Delle-case Emmanuel 
Published: May 2016

A very important aspect of offshore operations is the risk associated with flow assurance issues, with hydrates the most prevalent of them. The risk of hydrate formation brings the possibility of hydrate plug formation in the line which usually takes a long time to dissociate. Typically, connecting the wellhead with the manifold, the jumper is usually not insulated and has low spot sections where the water can accumulate - making it one of the most critical locations especially during a restart.

During this investigation a jumper-like facility was operated at atmospheric conditions with oil, gas and water to permit the study of different operating parameters. These parameters provided a better understanding of the water displacement during restart to predict the operating conditions that pose the greatest risk for hydrate formation.

The single phase gas restart experiments showed that initial liquid hold-up had minor impact. Variables impacting displacement were the gas restart velocity, density and viscosity of the fluid. In the two phase gas re-start experiments, water cut played an important role on the liquid removal and the fluid properties (viscosity and density) were found to play a more complex role. Overall, gas re-start at lower velocities promoted less disturbance to the water phase whereas higher velocities pose greater risk due to the considerable mixing involved. During the liquid restart experiments - one jumper volume at the lowest tested velocity removed most of the water from the jumper. Higher liquid restart rates were more effective pushing the water out of the jumper, but lower restart rates promoted more mixing.

Results of this project were compared to a commercially available multiphase transient simulator and found to be a match on the overall flow displacement but not on the final liquid content.

Introduction

Limited space and higher costs are typical problems associated with offshore operations, but another important aspect is the risk associated with flow assurance issues such as hydrate formation. They are crystalline compounds that form when water (host molecule) and methane, ethane, propane, etc (guest molecule) are present at low temperatures and high pressures. Seawater temperatures can get down to just above freezing temperatures resulting in significant heat loss from the fluids to the environment. When producing hydrocarbons (oil and gas) and water at these temperatures and relatively high pressures, the risk of forming hydrates is present.

There is a high risk of hydrate plug formation in jumper sections during restart operations. The jumper is a section of pipeline that connects the wellhead with the manifold. It is usually not insulated and has low spot sections where the water can accumulate, especially during shut down operations. Upon restart, gas contacts and displaces the water, creating hydrates plugs if no inhibitor is used.

One of the objectives of this investigation was to design and construct a jumper-like facility that operates at atmospheric conditions. Experiments with oil, gas and water were run to study different operating parameters and to gain a better understanding of the water displacement during restart.