Optimized Well Plug & Abandonment Methodology Applied on a Brownfield towards Future Development Offshore Malaysia
Authors: Costeno Hugo Antonio , Mendoza Luis Daniel , Djohor Mohamed , Curteis Charles , Raziyev Mukhamed , Cherchawankul Teerasak 
Published: May 2016

Abstract
A Workover or sidetrack is often performed, in brownfields, to revitalize idle wells or to produce alternate zones. Recently, with a larger number of fields being redeveloped; the proper plug and abandonment (P&A) of donor wells gained relevance.
This is a study of the evolution of the P&A methodology in a brownfield, offshore Malaysia, where engineering techniques and risk management strategies have been developed into a consistent approach to well P&A. The methodology has allowed economic access to reserves and has become a process that can be applied across the field based on well configuration, best practices and current technologies. The operations entail not only intervening wells for gravel pack removal, fishing of mechanical obstructions and retrieval of completions, but also isolation of completed reservoirs from surface whilst isolating cross flow between them, which is of paramount importance in a brownfield with plans for future enhanced oil recovery (EOR).
Challenges, such as lack of information and the uncertain condition of ageing wells related to corrosion, leaking elements, zonal isolation, annulus pressure and well integrity; as well as inadequate maintenance, mechanical obstructions and failure of existing downhole equipment have been successfully managed in all cases.
Key processes include extensive data gathering and upfront well investigation and preparation for contingency planning. The wells sequence has been optimized to minimize the impact of un-foreseen events; and the decision making process has been drafted to cover for a wide range of situations.
Results show reserves that have been accessed at 40% the cost of a sidetrack, by retrieving old gravel pack assembly and workover the well; also, sidetrack wells have enabled reaching reserve opportunities in the field without the costly addition of slots to offshore platforms. This consolidates the methodology for its further application in the field with the potential to be implemented on other similar redevelopments.

Introduction
As producing oilfields mature, production and recovery rates decrease, leaving companies with the challenge to extend the economic life of the field and to slow down the decline. In brownfields that have reached the production plateau, cost effectives techniques are required to maximize oil recovery while maintaining good project economics. Completing additional zones or repairing existing wells are techniques commonly applied to keep up production rates; while infill drilling is applied to access unswept hydrocarbon accumulations.
In offshore fields, the redevelopment plans of mature fields are challenged by the limitations of the existing facilities or the high cost of new installations. Specifically, for infill drilling in an offshore brownfield, well slots are required and not always there are slots left available from the original development.
To optimize expenditure in surface facilities and to prevent the cost of new installations, well slots are made available with techniques such as deck extensions to drilling platforms or by identifying slot recovery or sidetrack candidates. Sidetrack or slot recovery techniques require proper abandonment of the donor wells to prevent cross flow between production zones, contamination of aquifers or hydrocarbon flow to surface. The abandonment operation must be cost effective to prevent the cost burden on the infill wells.
This paper describes the abandonment techniques and the standard approach to prepare wells for sidetrack infill drilling in an offshore field. The wells that have been abandoned for sidetrack are multi-zone oil producers with dual string gas lift completion; producing zones ranging from two to six, and with gravel pack for sand control.