Requalification of an Older California Platform: API and Risk-Based Approaches
Authors: Miller T.M. , Dolan D.K. , Eskijian M.L. , Craig M.J.K. 
Published: October 2008

An aging infrastructure of oil and gas facilities in the Gulf of Mexico and offshore the West coast poses structural risk management issues. These issues are compounded, firstly, by enhanced drilling, recovery and operational techniques which tend to prolong the economic life of the field and hence the required service life of the platform; secondly, by uncertainties associated with the present condition of these structures; and thirdly, by a heightened sensitivity to safety within the industry.

This paper briefly discusses the evolving efforts by industry and regulatory agencies to address these concerns, in terms of establishing assessment procedures and performance criteria for aging facilities.

The paper describes, by way of illustration, the requalification efforts on one 25 year old West coast platform. A planned waterflood operation will extend the platform's service life by at least 20 years.

The merits and disadvantages of two assessment procedures used to establish the upgrading necessary for continued safe operations on this platform are discussed. Explicit risk acceptance criteria are not addressed.

This paper addresses risk posed by structural failure only. Risks from human, organizational and other errors are not addressed. It is recognized that these are a greater source of risk than that associated with structural failure.

ACCEPTABLE PERFORMANCE

Through such projects as AIM1 and regulator requests to reanalyze selected aging platforms2, it is recognized that some of the industry's older offshore facilities do not conform to current design standards.

This problem of structural geriatrics is common to many other industries such as air transportation, the nation's highway infrastructure, and the shipping industry.

For the upstream oil and gas industry, it is generally accepted that any assessment of existing platforms must address the probability of structural failure and the consequences of that failure. Both of these factors are clearly facility specific, and therefore require case specific analysis.

The probability of structural failure is a function of many types of accidental and environmental events, including storm, seismic, ice, explosion and ship collision loadings. The probability of collapse (or complete loss of serviceability) depends in part on the structure's original design criteria; cathodic protection and maintenance history; the extent to which the structural condition of the jacket is known; the (in)ability to control extreme loads; extreme event combination criteria; extreme event prediction uncertainties; and the remaining anticipated service lifetime of the structure.

The consequences of a facility's structural failure depends in part on local environmental and political sensitivities, the number of personnel anticipated to be aboard during an extreme event, and the importance of the facility to the operator's cash flow. On the West coast, failure consequence is complicated by the possible occurrence of a significant earthquake. In the Gulf of Mexico, there is usually sufficient time to evacuate platform personnel in anticipation of a severe storm. There is no such advanced warning in the case of earthquakes.

The need to requalify an old platform offshore California arose because the platform's service life will be extended to accommodate a proposed waterflood.