Finding safe ground for deepwater development: integrated probabilistic geohazard assessment iPGA for pipeline routing and facilities

The paper presents an integrated probabilistic geohazard assessment (iPGA) method developed in recent years by several leading offshore oil and gas companies for the evaluation of risk to subsea pipelines and facilities. The approach builds on the practice of establishing regional ground models for land-based engineering projects, in which the complete geological history of the site is used to predict the performance of the ground in response to engineering work and to identify the likely presence of geohazards. A considerable challenge in deepwater subsea environments is reconciling the scale and frequency of geohazard features and processes about which little is known and which at first sight can appear to be showstoppers to development. The iPGA method has many benefits over the more typical deterministic approach as it provides a systematic, iterative and rational approach to addressing uncertainties and quantifying the likelihood and impact of geohazards on subsea pipelines and facilities over the life of development. Presentation of outputs in the form of numerical values of geohazard event frequency, probability of a hit and damage outcomes, together with probability maps, is more readily understood and transferable to support engineering design and risk reduction. Experience from major projects around the world demonstrates the considerable value of the iPGA method in finding safe ground for the routing of pipelines and siting of facilities. The paper illustrates the various stages of the iPGA method which provides the industry with a new standard for the evaluation and mitigation of geohazard risk to deepwater development.