From the climate-controlled cab, all functions are monitored and stored for future reference.

One of the greatest challenges facing the industry today is how to identify, quantify and mitigate the risk factors affecting flow assurance by designing tools to address and handle blockage problems in extended reach flow lines and pipelines through flow remediation.

Crude oil is a complex mixture of hydrocarbons that consist primarily of paraffin, asphaltene, naphthenic and resin. When oil, gas and water are comingled inside the pipeline, several potential problems can occur:

- Wax and asphaltene can build up on the flow line wall, creating an excessive pressure drop or total blockage of the line;

- Water and hydrocarbons can form hydrate plugs that can block the line;

- Corrosion occurs with a high water cut; and

- Scale deposits can form from incompatible water.

As the temperature of the crude decreases, the heavy components like the paraffin wax (C18-C60) will start to precipitate out and deposit on the wall of the pipeline. As this process continues over time, the internal diameter of the pipeline is reduced and can eventually become blocked off completely.

Another issue commonly encountered in pipelines is asphaltenes, components in oil that are insoluble in pentane and hexane, but soluble in toluene or benzene. Asphaltene solids start to precipitate when excessive amounts of pentane or hexane are added to the crude. Asphaltene solids are dark brown or black and do not melt like paraffin wax. Mixing reservoir fluids with different gases or mixing two oil streams can also induce asphaltene precipitations (Wang, 2003).

Typically, these pipelines would be pigged with a poly-foam pig to remove any obstruction that would form by coating the walls of the pipe. Under severe conditions these lines would have to be pigged using multiple pigs with graduated outside diameters. In many cases, the pigs would become stuck in the pipeline and encased by the obstruction — causing additional delays and costs to the operator.

The CoilTAC Thruster System from Warrior Energy Services is a solution to flow assurance and extended reach flow line remediation. It is a combination of surface and subsea equipment that is used in removing buildup and blockages that form on the inside of pipelines. The CoilTAC System was designed specifically to extend the reach of CT far beyond its conventional limits while traversing a minimum 5° radius and in line sizes with internal diameters from 2.750 in. and up.

Thrusting and jetting

This system combines a conventional CT unit and a fluid handling system with patented technology. The system is made up of a purpose-built control console with an integral manifold system and the CoilTAC Thruster. The system provides a jetting action ahead of the Thruster while generating a thrusting force as it moves down the pipeline. The thrusting force provides a means to both pull and push the coiled tubing, increasing the reach potential. Simultaneously thrusting and jetting ahead of the tool with treatment chemicals applied directly to the pipeline obstruction cleans further and more efficiently than conventional CT conveyed methods. It is one of the only options to remove a complete blockage without cutting the line.

When washing or thrusting forward, the fluid is pumped down the annulus and the returns are taken up the coiled tubing. The Thruster’s internal ports allow the fluid to move from the annulus to the washing nozzles at the front of the tool. To control the thrusting force generated by the tool, a back-pressure valve spring is preset to open at a given pressure. This spring is optimized to provide the necessary thrust while providing the maximum flow rate to wash the line. As the tool encounters a buildup on the wall, there will be a noticeable drop in the surface weight indicator. This is a result of the injector head at surface feeding the tubing faster than the Thruster is washing ahead. As the tool washes through an obstruction, the surface weight is regained. To optimize the washing action of the thruster, custom built nozzles can be used.

Reverse thrusting is accomplished by reconfiguring the surface manifold to redirect the flow path to pump down the reel while taking returns up the annulus. This induces a high-pressure area at the front of the Thruster, assisting in pulling the CT from the line. Like forward thrusting, the flow path goes through a back pressure valve that regulates the reverse thrusting pressure.

Control console

The control console allows the operation supervisor to oversee all the operations from the CT, pumping and the fluid handling systems while being able to control the manifold arrangement from a single location. The console provides functions essential to a successful operation. The entire system (control cabin, manifold, data acquisition, tool box) is in a single lift package.

The manifold is mounted in front of the console to allow the operator to visually verify the valve positions before commencing an operation. All manifold functions are pneumatically operated inside the console. In addition, an air regulated fail-safe open throttle valve is installed on the manifold to prevent over-pressuring the flow line.

Data acquisition

The forward section of the control cabin is designed to operate the manifold, monitor all functions of thrusting operations, store all data using the Orion data acquisition system, and communicate changes as they arise — alerting the operator immediately if something looks astray. Analog gauges monitor pipe weight, pipeline pressure, pump pressure, reel return pressure, pump rate, total fluid pumped and total fluid returned. In addition to the functions listed above, the data acquisition system also monitors and stores pipe weight, pipe (line) speed, depth and pit levels.

The data acquisition system allows for visual and audible alarms to be pre-set by the operator. Communications are provided via two-way headsets to all individuals directly involved with the operation. The combination of analog and digital inputs assures failsafe operations even if electrical power is lost.

Flow line remediation

The service company recently used the system to successfully remediate a flow line in the Gulf of Mexico. The 3.5-in., 35,000-ft (10,675 m) oil production line was plugged with paraffin and all attempts to dislodge the plug had proven unsuccessful. The service company mobilized the system, CT, fluid pumping and thermal equipment via lift boat to the location. A temporary riser was installed to facilitate entry into the line from the work deck. Once engaged in the flow line, the Thruster pulled the CT through a 5° bend to a distance of 9,658 ft (2,945 m), removing the blockage and bringing the line back to full production. A proprietary blend of solvents was used to dissolve the plug and bring the remaining solids to the surface.