CASE STUDY: COGNAC CONDUCTOR REMOVAL

Cognac is a fixed platform in Mississippi Canyon Block 194. It is one of the few fixed structures in over 1000” feet of water. A strategy was put in place to recover 4 slots on the platform to carry out plans for 4 new wells to increase production

Mactech performed the drilling and pinning portion of the slot recovery, as well as cutting the conductor into sections, as it was pulled out of the of the slot. The sections were cut into manageable sections, so the facilities crane could lift and lay down the section. The lengths varied by well because the cranes weight rating changed at different radius intervals from the crane’s pedestal.

Mactech had previously completed smaller slot recovery work scopes for Enven in a safe and cost-effective manner.

ALTERNATIVE METHODS CONSIDERED

A guillotine saw was considered for the cutting portion of the project, but a Diamond Wire Saw (DWS) was ultimately chosen because of the efficient cutting and remote operation from a safe distance to help minimise the risk of an injury.

STEPS TO JOB COMPLETION

  1. Mactech conducted extensive job planning and analysis of lifting pin load capacity and dynamic factors to ensure the safe recovery of the conductors without damaging the platform.
  2. Mactech’s 30i DWS was placed on the work deck and placed on caster wheels enabling the saw to roll into position for each cut, rather than suspending the saw by crane, increasing productivity.
  3. As each conductor was removed, Mactech had it’s dual pin drill (DPD), set up on the production deck of the platform and the DWS on top of a pulling unit. This set up allowed Mactech to simultaneously drill and cut each section of pipe at the same time, increasing the efficiency of the operation.

CHALLENGES AND ADVANTAGES

Being one of the deepest fixed structures in the world, there was not a lot of experience to reference in removing conductors of the length or weight encountered on Cognac.

The Platform rests in 1124’ of water and is roughly 1,220’ from the BML cuts to the wellheads. This meant estimated conductor weights exceeded 300 tons each. Mactech analyzed, designed, and manufactured lifting pins to support this weight.

Cognac has 64 well slots on the platform, 62 of them had been drilled and had conductors in place. While recovering 4 of the conductors, leaving the platform with 58 intact wells, had any damage been done to the platform it could have not only jeopardized the future drilling program but production from the existing wells.

The Platform has been around since the 1970’s, and the records of which strings were grouted, and the elevation of the grout were not clear. Mactech had to plan for the worst-case scenario, supporting the weight of the inner strings and grout on our lifting pins.

In total Mactech drilled 574 holes for lifting pins, and made 274 Diamond Wire cuts.

Throughout the duration of the job Mactech had only 15 minutes of downtime on the DWS to replace a sheared roll pin, and no downtime on the drill or supporting hydraulic systems.

RESULTS

The project was completed approximately 1 week ahead of schedule with no damage to the platform or equipment. Mactech had no reported injuries.

IMPORTANT JOB STATISTICS

  • (4) wells, +/- 1,220’ each
  • (1) Well came up intact, all (3) strings
  • (1) Wells came up in (2) pieces, 9-5/8” then 16” & 26” grouted together
  • (1) Well came up with all (3) strings individually
  • Total linear feet was approx. 9,600’ of pipe recovered.

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