In producing offshore oil and gas fields there is a need for maintaining flow assurance in the associated pipelines. Restricted and plugged pipelines result in loss of production which is loss of revenue. It is common for these pipelines to exceed the length that can be reached by conventional coiled tubing when cleaning obstructions becomes necessary. Paraffin, asphaltine’s, hydrates and sand are a few of the contaminants that can obstruct flow and cause plugging. Historically, pipeline intervention has been limited to conventional coiled tubing with a reach of only +/−5,000’. A typical maintenance practice involved “pigging” the pipeline with a poly foam pig to remove any obstruction. Under severe conditions multiple pigs with graduated ODs were used. The problem with the poly foam pig is that the flexibility allows it to be forced through a smaller ID, leaving the restriction in place. CoilTAC® (Coil Thrust and Carry), developed by Superior Energy Services, was designed specifically to extend the reach of conventional coiled tubing for pipeline intervention while negotiating a minimum 5D bend. The Thruster was designed for line sizes with internal diameters from 2.900” up. This Thruster system eliminates the compression force on the coiled tubing and has been proven to 14,800’, and it has the ability to exceed 50,000’. The Thruster utilizes a “mechanical intelligence” which is present into the thruster with takes into consideration applied force parameters prior to the cleanout procedure. The key factors are: working pressure of the pipeline, length of the pipeline and the length and size of the coiled tubing to be carried by the thruster. The forward motion of the thruster is initiated by annular pressure applied between the coiled tubing and the inside diameter of the pipeline. The pressure energizes the cups and moves the thruster forward. At a preset pressure, a check value opens inside the thruster allowing fluid to pass to the front of the tool and exit through a series of ports. This causes a washing/jetting action in front of the thruster as it moves down the pipeline. The debris that is removed from the pipeline is returned through the center of the thruster. Retrieving the thruster is accomplished by pumping down the center of the coiled tubing which applies pressure to the front of the tool to reverse the Thruster out of the pipeline. The returns during reverse thrusting are then taken on the coiled tubing/pipeline annulus. Pump pressure moves the thruster in and out of the pipeline not the coiled tubing injector, thus eliminating the helical buckling forces and extending the reach of the coiled tubing. Historically, paraffin-laden pipelines had to be abandoned and new lines laid at great expense to the operator — it was difficult to abandon subsea pipelines without complete removal. Now there is an option with the CoilTAC® system.
Inter-helical and intra-helical buckling analyses of tubular strings with connectors in horizontal wellbores
