Annelida, a Robot for Removing Hydrate and Paraffin Plugs in Offshore Flexible Lines: Development and Experimental Trials

Methane hydrates and paraffin plugs on flexible lines are concerns in offshore production. They may stop wells for months, causing high financial losses. Sometimes, operators use depressurization techniques for hydrate removal. Another strategy is using coiled tubing or a similar unit to perform local heating or solvent injection. However, frequently these strategies are not successful. In those cases, a rig may perform the operation, or the line may be lost. We developed a robotic system to perform controlled local heating and remove obstructions. The system developed can access the line from the production platform. It uses a self-locking system to exert high traction forces. An umbilical with neutral buoyancy and low friction coefficient allows significant friction reduction. It allows moving upward and in pipes with a large number of curves. Coiled tubing and similar units cannot do that. Carbon fiber vessels and compact circuits give the flexibility to move inside 4-in. flexible pipes. In addition, a novel theoretical model allows the cable traction calculation using an evolution of the Euler-Eytelwein equation. Experimental tests validated this model using curved pipes, both empty and filled with fluid, and using different loads. Experimental tests also confirmed the external layer traction resistance. Furthermore, the carbon fiber vessels were pressure tested, indicating a collapse resistance of 57 MPa (8,300 psi). Besides, exhaustive tests of the onboard electronics and the surface control system guarantee the communication reliability. In addition, a theoretical model allowed the design of the 25 kN (5.6 kip) traction system considering the self-locking system, the contact with the wall, and a diameter range. Four prototypes allowed us to compare hydraulic and electric drive systems, validate the self-locking mechanism up to its limit, analyze the hydraulic system for leg opening and translation, and prove the traction capacity. Finally, a theoretical model allowed the local heating system and the temperature to increase. The experimental validation of the system on a cooled environment demonstrated its ability to increase temperature. Further, it allowed the obstruction removal in a controlled manner, avoiding damage to the polymeric layer of the flexible line.