Setting plug & abandonment barriers with minimum removal of tubulars

Abstract

The useful life of an offshore well is determined by the reserves which it contacts, the pressure support within the reservoir and the continued integrity of the wellbore. When a well has reached the end of its lifetime, plugging operations have to be conducted before permanent abandonment. Conventional Plug and Abandonment (P&A) operations will often require removing a section of the casing in order to create cross sectional barriers for well abandonment. Recently developed and field tested technology has the potential of efficiently setting cross sectional reservoir barriers without casing removal. Access to the annuli can be achieved through perforation and then the perforated interval can be washed prior to setting a P&A barrier. By deploying a wireline rig-up it can be possible to set a reservoir barrier prior to removal of the previously installed production or injection tubing. Wireline work can also provide information about the well integrity which can determine the potential for setting further reservoir barriers with minimum removal of tubulars. Further development of technology necessary to safely abandon wells with minimum removal of tubulars can provide cost efficient and robust plugging methods for abandoning offshore oil or gas fields without the need of deploying a drilling rig. This thesis will introduce methods of setting P&A barriers with minimal removal of tubulars as the main focus. Descriptions of various plugging operations will be given. Considerations regarding the critical factors encountered during plugging operations will be discussed, more specifically the current condition of wellbore integrity and the barrier envelope necessary to prevent uncontrolled release of hydrocarbons during or after plugging operations.