Safe, Robust and Efficient Through Tubing Abandonment

Abstract

There is a growing need for robust and efficient abandonment approaches with many oil and gas reservoirs nearing their economic lifetime. The Through-Tubing Abandonment (TTA) approach can deliver safe, robust and efficient isolation and reduced environmental footprint in keeping with ‘As Low as Reasonably Practicable’ (ALARP) principles. This paper provides guidance on how to select TTA candidate wells, including wells with gauge cables present in the permanent isolation interval, and provides operational advice to obtain a quality abandonment. The industry has been abandoning wells via through tubing cementing methods for decades which has resulted in significant progress in the understanding of the applicability of the methodology and commensurate development of suitable technologies to deliver reliable long-term isolation. This paper will present the latest on selection criteria to screen wells for TTA. It will further propose cement placement and verification methods, necessary barrier lengths and risk-based decision making on the acceptability of gauge cables as part of the final permanent well barrier element. The recent insights in TTA technologies and their use are described. These include demonstrated technologies such as expanding cement and vibration tools to enhance cement placement and options to log and verify the isolations. Testing results on cement sealing with gauge cables incorporated in the cemented annulus are also presented. Furthermore, promising emerging technologies such as methods to centralize the tubing to improve cement placement will be described. Recent TTA applications in Europe, onshore and offshore, are presented as examples to illustrate current industry experience and the viability and reliability of such approaches. A generally accepted, safe, robust and reliable approach towards TTA in keeping with ALARP principles common to the industry is pursued within this paper in order to enable acceptance and growth of TTA and associated technologies, and thereby further enable the wider application of rigless abandonment across the industry.