Abstract

Until around 1990 the main marine geohazard risk addressed solely from geophysical data was the presence of shallow gas. Presence had been described using a number of non-standard approaches for its potential presence - distinct from the actual risk it presented to operations. In the 1992 UKOOA Guidelines for the delivery of marine rig site surveys a standardised nomenclature was suggested that was largely taken up as a standard by the industry.

Ironically, at exactly this point in time, as the industry had begun to move off the shelf and into deep water a number of other issues had started to present themselves: shallow water flow, chemosynthetic communities, hydrates etc. for which the industry has yet to publish a set of standard guide points on the risk of presence.

In contrast with shelf settings where the risks to operations were generally around shallow gas, anchoring and footing assessment and clearance, the industry is now faced with complex slope and deep-water settings where the sources of risk can be multiple, over printed, and inter-related. In such settings early effort in the exploration and production cycle is required to ensure appropriate data are gathered and assessments delivered in proper time for drilling and facilities engineers to either avoid the presence of hazards identified or properly mitigate their presence through appropriate engineering design.

This paper will outline a suggested methodology both to assess fundamental geohazard complexity and manageability, at the basin or fairway scale, and thence suggest specific risking criteria for the presence of individual geohazard elements at a specific location such that engineers can clearly, and consistently, understand potential hazard presence and thence the need to adopt appropriate risk mitigation methods in engineering design.

Introduction

An unrecognised geohazard translates into risk being carried forward into operations with the possibility of a major accident through use of an operational plan that fails to avoid, or mitigate, the unidentified risk faced by the activity. The avoidance of this situation has been the underlying driver of marine geophysical site investigation in delivery of hazard or site surveys, as they are often referred to, over the last fifty years.

To properly assess and describe hazards across an offshore site requires appropriate front end loading (time) for the project to understand the relative level of complexity faced across a site, allowing design and delivery of a suitable set of geophysical data to assess the hazards present in reflection of the operations planned, and finally by the application of clear and consistent methodologies to identify and describe hazards in a manner that is unambiguous to the end users of the work: engineers.

For the majority of the first thirty years of the marine geophysical site investigation industry (1960–1980s) however, techniques developed originally on the shelf, encouraged both by industry or regulatory practices, did not always permit this to be achieved in a manner that was always consistent with the risks faced at an individual site or location.

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