At The Cutting Edge—Rigless Subsea Production Well Abandonment (Page 1 of 3) By Article provided by Well Ops, 1 Sep 2009

Southeast Asia's first rigless subsea production well abandonment has been completed using a specially engineered riserless tooling system. Well Ops Southeast Asia successfully abandoned four subsea production wells in the Elang-Kakatua field by deploying a suite of proprietary equipment and specially engineered, project-specific tooling from a monohull work vessel.

Located in 100 m water depth, the Elang-Kakatua field comprises four subsea production wells tied back to the Modec Venture floating production, storage and offloading (FPSO) vessel.

The wells were completed in 1998 with conventional tubing strings and were fitted with early generation Cameron Spool Trees. With the field decommissioned in July 2007, Well Ops was contracted by the operator, ConocoPhillips, to abandon the subsea wells.

Focusing on lightweight well intervention, using open-water running tools from a standard vessel, Well Ops avoided the high costs and long lead times often associated with using a rig. Saving up to 30% of the cost of a conventional abandonment campaign, Well Ops managed the project in three stages, with the well abandonment operation for each well completed in eight days.

"Drilling rigs are traditionally used for subsea well abandonments, but they have limitations. They're expensive, require high numbers of personnel and can stretch a project timeline out significantly," said Rob Jones, Wells Ops Senior Project Manager..

"And then there are the environmental and safety risks associated with using explosives for severing wells.

"We wanted to have a better solution for our clients, which is why we've developed a complete suite of abandonment and intervention tools that can be deployed from a standard work vessel."

With around 3,800 flowing subsea wells around the world, and many more that have been plugged but not yet abandoned, safe and effective abandonment is a growing concern.

Well Ops' lightweight subsea abandonment system includes purpose-built rigless tooling technologies that are used in conjunction with a unique onboard deployment system. This enables all intervention and abandonment work to be carried out without the use of a rig or riser.

A key component of the rigless abandonment system is a patented wellhead removal tool using an entrained-grit, water-jet cutting system. With the ability to sever multi-casing wellheads and cut jacket piles and caissons, the AXE cutting tool uses medium pressures of 10,000 to 15,000 psi. AXE is capable of entering and cutting wellheads with 7" casing, and severing through 7", 9?", 13?", 20" and 30" in a single-pass cut.

Well Ops' proprietary cement injection tool was also used on the Elang-Kakatua field. Designed specifically to perforate the production casing, the cement injection tool monitors and controls the annular pressure and sets a cement plug in the casing itself.

"Our technology eliminates the need for explosives or a wireline perforating system, and by operating hydraulically from the surface, we can run equipment into the well using a hang-off tool and lifting wires," said Jones.

"We've developed the system so we can combine perforating, pressure monitoring and cement plugging tasks in a single deployment, which is cost-effective and faster than traditional cementing techniques."

Well abandonment in three steps

The rigless well abandonment at the Elang-Kakatua field was completed in three steps:

  1. Flushing the flowline and well kill from the FPSO;
  2. Disconnecting the flowline and terminating the Christmas Tree (XT) production and annulus flange from the dynamically positioned work vessel; and
  3. Cementing, recovering the XT, and severing and recovering the wellhead.

"The first step was to mobilise our well kill pump skid onto the Modec Venture, then all four production wells were flushed and killed with seawater and brine so that the flow lines could be disconnected," said Jones.