The minimum accepted industry standard for the rational, risk-based, acceptance criteria for jack-up operations in the Gulf of Mexico, which may be applicable to other tropical revolving storm areas, is outlined. The acceptance criteria are based on a rational examination of the way jack-ups are now used in the Gulf of Mexico. This articulation takes into account consequences of failure and is reported in the same framework as the ISO TC67/SC7 working group on fixed platforms has developed its guidance.

ABSTRACT

The minimum accepted industry standard for the rational, risk-based, acceptance
criteria for jack-up operations in the Gulf of Mexico, which may be applicable
to other tropical revolving storm areas, is outlined. The acceptance criteria
are based on a rational examination of the way jack-ups are now used in the
Gulf of Mexico. This articulation takes into account consequences of failure
and is reported in the same framework as the ISO TC67/SC7 working group on fixed
platforms has developed its guidance.

The recommended practice for jack-up rigs developed over the last few years,
known as SNAME 5-5A has been proposed as the basis for site assessments in an
ISO standard. This SNAME document is divided into two parts T&R 5-5, the
Guideline document, and 5-5A, the “Recommended Practice”a. The Guideline
document is generally accepted by all sectors of the jack-up industry. It is
only with the “Recommended Practice” that the disputes arise. The
worldwide impact of this 5-5A bulletin, as the document is now written, appears
to severely, and perhaps inappropriately, curtail jack-up operations in tropical
revolving storm areas.

The entire evolution of a basis of acceptable risk in areas where personnel
evacuation infrastructure is in place, is vastly different from that which evolved
from operating in the North Sea environment. The criteria being used in the
Gulf of Mexico have not been set forth in a specific document to date. This
is an attempt to capture what the authors believe is the current acceptance
criteria identifying what is now, implicitly, acceptable for the various stakeholders
in terms of site specific acceptance criteria.

This pragmatic existing practice is then formalized in terms of a table of
five acceptance criteria levels which document the framework for acceptability
of site assessments for these special tropical revolving storm areas. The methodology
of the acceptance criteria developed for fixed platforms has been followed.

If it is confirmed that this is current practice accepted by the technical
community is valid, it can be used to develop the criteria for a Regional Annex
that can be put in place as part of ISO/TC67/SC7/WG7’s work.

KEYWORDS: Jack-Up, Gulf of Mexico, Site Assessment, Acceptance
Criteria

PREFACE

This paper presents a risk methodology for the assessment and acceptance criteria
for mobile offshore selfelevating units in the tropical revolving storm area
of the Gulf of Mexico, based upon categorizing consequences of failure. Insofar
as the infrastructure for demanning and the general conditions may be similar
to the Gulf of Mexico in other locations around the world, it may be generally
applicable to other regions. Guidance on the requirements for plans for demanning
is identified herein. Existing Rules and Regulations by both Classification
Societies and Governmental Agencies cover the ‘design’ conditions.

Such site assessment criteria should be construed only in the context of site
assessments where demanning is intended, and demonstrably feasible. Clearly,
responsible persons should review the site assessment criteria in each particular
case to ensure that it is appropriate for the particular situation, and that
normally is the function of the owner, and if beyond the limitations of the
vessel operating manual, of the appropriate Further technical work is required,
with case studies, and reliability tools, to confirm the appropriateness of
this rationally developed criteria. It may be appropriate to view this criteria
in the same context as that developed for the mooring systems of floating structures
1 and that which has been under study by Gulf of Mexico practitioners on fixed
platforms 2. Although the criteria proposed herein have similar results to those
derived by reliability principles 2, the jack-up community has generally embraced
a ‘rational basis’ for deriving the limits of serviceability of their
units.

If the jack-up community find the format and style of the criteria presented
in this discussion paper appropriate, it will be necessary to undertake calibration
work to ensure that the details are consistent with existing needs and practice.
At its simplest level, this would entail undertaking a series of conventional
analyses using conventional engineering practice (LRFD and/or Working Stress)
and newly derived meteorological data (including joint probability data derived
for jack-ups, where necessary). At a more complex level, it may be necessary
to extend existing analysis techniques to cover the limits set out within this
document (e.g. equivalent of a fixed platform “push over” analysis).
This would allow much improved definition of “system failure” and
“deformation such as to prevent jacking down off location”.

The American Bureau of Shipping has led the development of jack-up standards
since the first designs were developed some 40+ years ago. These ‘design’
standards, modified as occasional problems developed, have served the industry
well. With increased knowledge of jack-up performance, ABS and the industry
are, as always, in a process of Rule examination to adapt to the ever increasing
demands of better calculation methodologies. This paper is not about ABS, nor
does it discuss the ABS Rule Requirements, nor ABS’s approach to the issues.
ENSCO and Rowan have served the industry very successfully, with over 1,000
jack-up rig years of worldwide operations, and their personnel have many more
years of
successful experience.

This paper does not reflect any of ENSCO’s or Rowan’s policies
in operating or siting jack-ups. Drilling contractors applying similar standards
have operated over 100 jack-ups for over 20 years in the Gulf of Mexico. The
authors, making no representation about the policies of their respective companies,
have joined together to write down what they believe has been the de-facto practice
of siting jack-ups in the Gulf of Mexico. Within the framework of this paper
the authors are not necessarily advocating the criteria – merely stating what
they believe to have been the generally accepted situation in the Gulf of Mexico.


Download below for whole article.