Top Tensioned Riser

Top Tensioned Riser Top Tensioned Riser (TTR) is supported in the floater to remain in acceptable vertical movement by the top tension force provided. The horizontal motions of the floater induce stresses in the riser base and at the top end near the flex or keel joints. TTR is applied for dry tree production facilities such as SPARs or tension leg platforms (TLP) that have small heave motion. By deploying separate heavy compensation system, TTR also can be applied on semi-submersibles. For the usage of drilling, production, injection and export, TTR runs directly from the subsea well to the vessel deck ‘s surface tree, supported by the tension by either buoyancy cans or deck mounted hydro-pneumatic tensioners. However, installing of buoyancy cans on spars is costly, time consuming and complicated compared to hydro-pneumatic tensioners which are widely used on spars and TLPs. In harsh environment and deepwater, the riser top tension requirements become significant to support riser weight and prevent bottom compression. Therefore, at some point when the wave movement is too drastic, TTR becomes technically unfeasible and uneconomical. A typical configuration consists of the following key components for a dual barrier top tensioned riser system. External Tieback Connector (ETBC) - provides the interface between the outer riser and the subsea wellhead and must accommodate the tension and high bending loads imposed by the riser. Lower Stress Joint - connects the riser to the subsea conductor casing at the subsea wellhead via ETBC, can sustain high bending stresses and fatigue loading. Internal Tieback Connector(ITBC) - act as the interface between subsea wellhead external tieback connector and inner riser. Standard Riser Joints - made up most of the TTR to below Mean Water Level (MWL). A dual pipe crosssection riser is utilized for production TTR, if the the inner riser fails during workover, the outer riser can retain the workover fluid and sustain hydrostatic head in the well. Splash Zone Joints - prevent corrosion and impact with thick wall and neoprene coating Hydro-pneumatic Tensioner - interfaces with the outer riser via a tension joint, maintain stability and control motion performance to ensure constant positive effective tension at the base of the riser under all loading conditions.

Figure: Typical Gulf of Mexico Tension Leg Platform (TLP) Production Top Tensioned Riser

Surface Wellhead - act as a suspension point for the inner riser and drill casing. Surface Tree - Control the flow of production fluid and also a injection point and a part of pressure relief systems. Flexible Jumper - conduct fluid between surface