Framework for reliability assessment and risk-based integrity management of sub-surface well subject to temporal and spatial degradation variability

The progressive loss of integrity of oil and gas sub-surface well tubing results from temporal- and spatial-variant deterioration mechanisms e.g., corrosion and scaling during lifetime. An optimal planning of integrity management should account for the uncertainties associated with temporal and spatial variabilities of these degradations to avoid disastrous consequences of failure. Risk-based approaches taking basis in the Bayesian pre-posterior decision analysis and methods of structural reliability, have the potential to form a rational basis for optimal planning of inspections and maintenance of the production tubing. However, at present, an integral framework for risk-based planning of inspection and maintenance for the entire tubing system is not available. In this paper an outline of such a framework for an integral risk-based optimization of inspection and maintenance of oil and gas production tubing systems is developed. The novelty of the framework is the consideration of the spatial (and temporal) variability of production tubing as a system consisting of several sections in different damage condition states as time evolves, in addition the framework is formulated based on the two severe failure modes of the tubing clogging and leaking due to scale and pitting corrosion respectively.