In the decommissioning phase of oilfield facility lifecycles, focus pivots from positive net present value to executing the care and preservation, then decommissioning in the safest and most environmentally sensitive manor, and at the lowest total cost of ownership. Asset Retirement Obligation (ARO) is a long-term liability carried on the balance sheet, as a provision for the cost to return a wellsite to pre-exploration condition. The reduction of abandonment and decommissioning expenditure (ABEX) in executing compliant operations is a key business performance factor, and critical in executing higher volumes of wells earlier than planned. In doing so maximizing value to company shareholders, residents, industries and government level stakeholders.

In the case study, an offline pre-abandonment and Phase I primary reservoir isolation project is presented, which seeks to maximize net project efficiency via offline wellbore intervention, executing the primary reservoir isolation of the wellbore via rigless techniques. This approach contributed to ABEX reductions by up to 40% per well vs the planned approval for expenditure (AFE) provisions taken for the operations.

The project execution structure utilized offline intervention and Phase I primary reservoir isolation of 81 wellbores, across 5 wellhead platforms and 47 days continuous operations. Operations were part of a simultaneous operation (SIMOPS) project, as an offline work front located on the wellhead platform (WHP) weather deck. A second work front for Phase II and Phase III well abandonment operations, is executed concurrently, from the jack-up rig cantilever above the WHP. Live well operations are conducted concurrently by both work fronts, through the Christmas Tree (XT) and pressure control equipment in Phase I, and through the drilling riser and blowout preventor for Phase II and Phase III, to maximize productivity when the rig is on location.

The scope of operations included wellhead qualification, wellbore access and preparation, well kill, injectivity testing, various wellbore preparation and cement placement techniques, pressure testing and lubrication of the wellbore. The operator's system engineering, design of operations and planning agility are key to its success. Acute focus was given to the batching of operations and delivery of these in a phased approach to increase productivity and maintain high service delivery through repetition of tasks.

The project successfully executed Incident Free Operations (IFO) with 100% productive time and facilitated combined project performance, which delivered wells up to 44% ahead of the planned AFE. To enable this, over 4.19 million feet of slickline was run, conveying 428 bottom hole assemblies (BHAs), preparing the wellbores to isolate 804 primary reservoirs, and 2 intermediate reservoirs.

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