The decrease of "conventional" hydrocarbons reserves and uncertainties of the current market, with the addition of enhanced oil recovery technologies which allow a longer productive life of oil fields, have made the life extension of existing wells more advisable than the drilling of new wells. In fact, the more and more challenging contexts in which new wells have to be drilled (remote locations, ultra-deepwater, harsh environments, sensitive areas, etc.) definitely imply higher investments and pose further safety risks and environmental concerns.
The concept of "well life extension" is essentially based on getting a comprehensive understanding of the current and future "health conditions" of wells, to estimate the "residual well life" and put in place a proactive monitoring and maintenance programme for ensuring today's well integrity while reducing the degradation rate of the expected future weakest Well Barrier Elements (WBEs).
To allow this, a specific methodology to the management of ageing fields has been developed, which consists of the following tasks:
Assessment of current WBEs conditions, to evaluate whether the well can be still operated safely. To this aim, the available well logging data and, more generally, all the existing monitoring and maintenance information can be used.
Design and execution of diagnostic tests, if required, to get more in-depth information on the well status.
Definition of the present safe operating envelopes of WBEs, and comparison of the results of the current condition assessment against the data specified in the original well design.
Execution of a Failure Modes, Effects and Criticality Analysis (FMECA), based on the failures occurred in the specific field and the use of international reliability databases, to identify the potential failure modes of WBEs and assess the related risks.
Estimation of the residual well-life.
Prevention of further deterioration of the present well integrity status, by selecting appropriate remedial actions through a cost-benefit analysis.
Definition of an effective monitoring and maintenance programme, to extend the well life without reducing its safe operational conditions.
A dedicated software has been developed to support the above tasks. Besides allowing the assessment of the current well integrity, it enables the identification of the future weakest WBE(s) and the estimation of the residual well life.
This paper describes the above Well Life Extension Methodology, along with the main results achieved from its implementation in two gas storage fields in France, in terms of enhancement of assets reliability, improved safety levels and minimization of both downtimes and costs associated to WBEs failures.
