With most of the major fields in the western off-shore of India being mature, the niche domain of well decommissioning is all set to experience its peak. The recent trends in the decommissioning industry indicate operators around the globe shifting towards fit-for-purpose alternatives to the conventional rig based decommissioning. However, with the day rates of Jack-up rigs slashed down to 35-40% of that of the pre-downturn period, entails us to revisit the strategy regarding the selection of the method for decommissioning. Therefore, this paper presents a framework that encompasses various parameters which serve as a guide to select an optimal method for a platform based well decommissioning. The paper initializes by detailing the associated parameter ‘Platform Specifications’ comprising of platform's layout (available free space and various Rigless packages’ footprint), load-bearing capacity and material handling capacity of the platform. Following which, the paper contrasts rig based and Rigless Well decommissioning on three critical domains of project management- [1] Operational constraints, [2] Time constraints and [3] Economic constraints, henceforth presenting a synthetic technoeconomic analysis for a platform based well decommissioning project. Inferring from the synthetic techno-economic analysis, the paper concludes that there are no visible cost benefits of selecting Rigless decommissioning over rig based decommissioning. The time and cost involvement in platform modification (if any) for undergoing Rigless approach, assimilated with the principle of economies of scale (in terms of wells spread over large number of platforms in the field undergoing decommissioning) and the ability to handle known and unknown uncertainties due to limited firsthand experience, further supports the rig based approach for platform-based well decommissioning in the current market. The paper re-establishes rig based approach as a potential solution for dry tree wells decommissioning and challenges the cost-effectiveness of Rigless solutions for decommissioning available in the market, owing to techno-economic viability and risk optimization in the current market scenario in the western Indian offshore region. Further, with subsequent knowledge sharing from operators having experience in both Rigless and Rig based abandonment on comparable platform layouts and well specifications in the region, the industry will tend to standardize and gain proficiency to develop a sustainable approach to well decommissioning.

The Cessation of Production (COP) from mature fields assimilated with the backlog of idle wells has entailed the operators to beef up the decommissioning projects in the industry. Following the recent downturn with the market going "leaner" in finances, the economic viability of any project, especially a D&A project is deemed paramount. The current trends in the industry indicate the paradigm shift towards rigless decommissioning as well decommissioning methodology from conventional rig-based operations. Though planned rigorously quite a good number of rigless P&A campaigns end up in cost over-run due to from "unknown unknowns", uncertainties of working on old wells and contingencies midway in the project thus entailing techno-management re-enforcement. However, this can be rectified by efficient candidate selection from the set of wells that are expected to undergo P&A. Therefore, the paper describes a framework that encompasses various parameters serving as an optimum guide for candidate selection of wells to undergo rigless P&A campaign, either partially or wholly. Of the operations involved in well abandonment, irrespective of the phase of the campaign a majority of them will be significantly impacted by well plan and parameters, cement integrity behind casing and data arability or quality of data available regarding these parameters. The paper describes these parameters categorically viz 1) Well parameters which include well plan, casing policy and seats, directional parameters such as well profile, inclination, horizontal drift, dogleg of kick-off (short radius/ long radius kick-off) and 2) Cement bond integrity between casing and cement (annular integrity) and the integrity between the cement and the formation. Considering the uncertainties involved in P&A operations such as the need to access the multiple annuli for placing barrier in the phase 1 of decommissioning due to poor cement integrity or due to sustained casing pressure in section B&C annuli or be it the contingencies in phase 3 associated with pulling of heavier tubular like 13 3/8 casing and conductor pile, pulling pack offs in wellhead, tag test of surface plugs, the paper discusses the impact of these parameters in the technology selection for the well P&A. Consequently, assimilating it with the technical limits of rigless options such as maximum load handling capacity of platform cranes, pulling capacity of jacking & Pulling unit, surface handling capacity for tubular of rigless package, limit on drift accessibility by E-line/ slickline in high angle and ERD wells, the paper presents the candidate wells for the selected strategy for well P&A. The paper strengthens the need for adequate planning for selecting candidate wells for a proposed strategy for decommissioning of wells, whether partially or wholly rigless, and presents a structured framework as a solution for candidate wells selection. Further considering the operator and regulator specific details, the framework can be customized and detailed for the particular regions and the fields.