Troika Subsea Production Template and Manifold System
Authors: Mclnturff T.L. 
Published: October 2008

One approach to subsea developments that has increased in popularity is the use of cluster arrangements in which the wells are situated around, but separate from, a central manifold structure. Advantages of such systems include the ability to utilize pre-drilled wells, potentially less impact by shallow water flow problems, and the ability to use the drilling rig to install the inherently smaller system components. The design of a cluster-type template/manifold system presents challenges unique to the type. The Troika template/manifold system design addressed such issues as pigability, pipeline and umbilical snag resistance, as-installed levelness, the need for a high level of thermal insulation, hydraulic supply and electrical signal distribution, corrosion protection, retrievability, expandability, component reliability and redundancy, and installability. Regarding installation, we believe the Troika template/manifold is the first to be installed by deployment via supply boat under the rig's moon pool.

Introduction

The BP-operated Troika production system is a subsea development in which BP, Marathon, and Shell each have a one-third interest. It is a cluster-type development in 2,700 ft of water in Green Canyon Block 200 in the Gulf of Mexico1. The manifold is tied-back to and controlled from Shell's Bullwinkle platform, approximately 14 miles to the northwest, by means of two 10–314 in. OD flowlines2 and separate hydraulic and electrical umbilicals (Fig. 1). The decision was made to utilize the GC-200 #1 delineation well previously drilled by Marathon, so the template/manifold would have to be located so as to allow completion and connection of that well to one of the system's eight slots. Since the GC-200 #1 well did not encounter any shallow water flow problems, it was felt that locating the remainder of the Troika wells in close proximity to that well would maximize the probability of the same results. Well spacing was driven primarily by the desire to eliminate gyroscopic surveys of the shallow portions of the wells, thus creating the need to separate the wells and template piles enough to prevent magnetic interference. A minimum separation of fifty-five feet was needed, so the proposed well locations were set at a separation of 60 ft k2.5 ft. Additionally, the well locations were chosen so as to provide a clear area adjacent to the flowline end of the template/manifold for jumper connections to the flowlines, and to minimize the possibility of impacting a well if a flowline were to be snagged and pulled loose. These same later considerations were given to the area adjacent to the pigging loop end of the template/manifold due to the possibility that the Troika system would be expanded into another area. This possibility was, however, given less weight in that a more restricted access corridor was preserved for the pigging loop end than for the flowline end. Each of the two 10–314 in. OD steel pipe jumpers which connect the manifold headers to separate flowline sleds includes a special load-limiting joint near the manifold end of the jumper.3 The joint is designed to part cleanly when the pull force exceeds the design limit, thus eliminating any damage to the manifold or template in the event of a pipeline snag.