Risk Management

Offshore structures, pressure vessels, pipelines, wells and process system are designed to assure a certain performance for the different operations during the service life. This is done according to given requirements and acceptance criteria, generally related to safety of personnel and environmental and financial risk.

In this context, risk management allows to formulate the best strategy aiming at obtaining the desired performance with respect to the acceptance criteria by means of classical decision analysis, where the objective is to minimize the risk function. In general terms, the risk is defined as the product of the expected value of the consequences associated to the failure mode F and the probability of the failure mode. Therefore, the first step into risk management is to identify the system with all its components, functionalities, failure modes and deterioration mechanisms along with inspection techniques and repair techniques.
Risk Screening
Figure 1: System identification and risk screening main steps (click to get a larger format)

Depending on local environmental conditions, design criteria and applied protective measurements, sub-surface wells are affected by different deterioration processes (e.g. corrosion and scale) causing progressive loss of integrity and production capability. The different deterioration processes will follow different patterns both in time and space depending on the choice of material, detailing of the completion and processes, operations and exposure to aggressive environment.

Current best practice identifies inspections as effective tool to control the degree of deterioration of the well completion. However, inspections have large impact on the operation of the well and are very costly (e.g. workovers), depending on the accessibility of the components that has to be inspected and therefore they are operated in a corrective framework. In addition, based on the outcome of the inspections, effective corrective repairs need to be identified and planned to assure continuity of operation and low deterioration rate of the well.

In order to maximize the benefit from an inspection, proactive inspection planning is needed, following the criteria of the best balance between the expected benefit of the inspections and the corresponding cost, taking into account that the inspection may lead or not to the choice of a corrective measure (repair). In addition, different inspection strategies (effort, quality, costs), as well as different maintenance techniques, may be available and lead to different effects when evaluating the risk based asset management strategy. By comparing the risk associated with different inspection and maintenance strategies, the asset management strategy implying the lower risk can be identified.

The aim of the risk management activity is the development of probabilistic models for the different degradation processes with the aim to predict the performance of offshore wells and the implementation of the Risk Based Inspection Planning methodology for identifying the best maintenance strategy for subsurface wells and assure operability for an extended lifetime reducing costly workovers.

Predictive maintenance model

Figure 2: Conceptual model for predictive maintenance using influence diagrams (click to get a larger format)