PSI - Issue 14

Praveen Bhat et al. / Procedia Structural Integrity 14 (2019) 656–663 Praveen Bhat, S. Karunanithi/ Structural Integrity Procedia 00 (2018) 000 – 000

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• Securing permits/approvals from the concerned authorities • Plugging and abandonment of wells (in case of well platforms) – killing the well, removal of packers, setting various cement plugs in the wells and conductor cutting & removal • Decommissioning of topsides/Cessation of production - Cleaning & purging hydrocarbons from production equipments and decommissioning the pipeline(s) • Removing the platform – Deck (super-structure) and Jacket (substructure) • Disposal of the platform - Deck (super-structure) and Jacket (substructure) • Clearing the site – Removing any remaining debris and verifying a clean site by trawling/surveys For relocation of the three platforms undertaken for study, the procedure from ‘ i' through ‘ v ’ are required to be complied with followed by relocation procedure including installation of a plinth structure, if required, for mating the parent jacket supporting the deck over it. The basic rules for decommissioning offshore installations referred to in the study are the Oil Industry Safety Directorate (OISD)/ International Maritime Organization (IMO) /OSPAR(Oslo-Paris) Commission guidelines and regulations. 2.2 Methodology of Abandonment and Decommissioning for the identified platforms In accordance with the applicable laws/regulations/international practices, an abandonment option has been chosen for the A, B & C platforms. A methodology has been worked out in line for relocation of the platforms • Carry out surveys and detailed engineering for the abandonment for safe, environment friendly, efficient and successful execution. • Mobilize a jack-up rig to the platform location and start well plugging and abandonment (P &A) operations and complete the operations for all the wells. All conductors shall be removed by the jack-up rig. • After successful well P& A at first platform the jack-up rig shall be moved to second and third platform location and complete the operations for all the wells. All conductors shall be removed by the jack-up rig. • Decommission the topsides using the hook-up barge; decommission the pipelines up to the desired location; Move the hook-up barge to next location and start decommissioning the topsides. After completion, demobilize the hook-up barge. • Fabricate the necessary clamps with suitable slings, stubs & lifting pad-eyes, etc. to enable carry out cutting and lifting operations. • Mobilize a derrick barge with the fabricated parts & reach first platform location. Also, mobilize a cargo barge. • Position the derrick barge and the cargo barge at first platform location • Prepare for deck removal; Cut the riser using divers/explosives; Remove/tie down the equipment; Cut the four • Severe the piles of jacket at 5m below mud line using explosives/abrasive cutting • Lift and remove the jacket along with appurtenances and place them onto the cargo barge • Clean the site and verify the same by underwater survey • Move the derrick barge and the cargo barge from the first platform location and position them at second platform location • Transport the decommissioned deck & jacket structures by cargo barge to onshore/offshore barge for refurbishment if any. 2.3 Refurbishment, fabrication & relocation for the identified platforms The strengthening/refurbishment requirement for the existing structure could incorporate the following features, as per the requirement: • Required transition pieces for the deck shall be refurbished or fabricated separately. • Required plinth framing structure (along with skirt pile sleeve) for the water depth adjustment shall be fabricated separately. • Demobilize the jack-up rig • Mobilize an hook-up barge deck legs of the platform near the pile cutoff level/transition piece level • Lift and remove topsides/deck and place them onto the cargo barge