A Unique X-Mas Tree Active Flowline Compensation Capability
Authors: Paulo C.A.S. 
Published: October 2008

On the objective of turning the subsea exploitation of oil/gas reservoirs more efficient, reliable and less expensive, various subsea systems may be considered amongst single satellite wells, subsea manifolds, templates-manifolds and others, each one having its own niche.

When considering deepwater templates-manifolds, with recoverable manifold enclosed, some linear and angular misalignments do occur between wellheads and manifold hubs, as a consequence of the natural clearances and manufacturing tolerances. Then a special system is required to absorb and compensate these deviations.

A special flowline connector has been conceived with the main objective of making it possible for a guidelineless tree to be simultaneously connected to the template-based wellhead and to the manifold piping end hub, in a deep water template-manifold project.

Full scale prototypes of a dummy template wellbay and a dummy x-mas tree have been manufactured. Dry tests have been performed, and the imposed misalignments were adequately compensated by the new flowline connector being presented in this paper.

INTRODUCTION

During the technical and economical feasibility studies for the development of Albacora field, different production systems were analyzed. Due to the water depth and other field characteristics, subsea based systems with floating processing facilities were considered the most adequate. Various subsea drilling and production systems were studied and the option of using template-manifold was, among others, also attractive.

A conceptual design of a deepwater guidelineless template-manifold was carried out. The project team has tried to use as much as possible field proven techniques for the equipments and operations involved. Nevertheless, when analyzing the simultaneous vertical connections of the x-mas tree to the template-based wellhead and to the manifold piping hub, a new problem was faced: the linear and angular misalignments. A new solution was adopted: the wet x-mas tree active flowline connector.

X-MAS TREE FLOWLINE CONNECTION OPTIONS

Basically, the options can be divided into horizontal or vertical connectors, each one having its pros and cons.

The horizontal connectors, like the ones being used on template-manifolds in Norway, have the advantage of being strictly composed of mechanical parts. No resident hydraulics, since all cylinders and plumbing are located at the connection tool. The disadvantage is the need of an external tool that requires one extra trip to connect the tree flowloop to the manifold piping hub, after the x-mas tree has been installed.

The vertical connectors have the advantage of allowing an one-trip operation to install the x-mas tree and connect its flowloops. All actuation is made hydraulically through the tree running tool. This one-trip operation will be also valuable at any time the tree has to be retrieved during field life for well intervention. The fact of being furnished with hydraulics for the connector latch/unlatch mechanism is not considered a problem, since this same principle is used at the x-mas trees wellhead connectors and at the flowline connectors of lay-away trees, with very good performance. The only problem is the very limited capacity of existing vertical connectors to handle linear and angular misalignments.