Underwater Technology
Vol 25 No 1
Autumn/Winter 2001
A Personal View
A Clarion call for clathrates
A Hunt
Technical Papers
Marine Aggregate Dredging in
the UK: A Review
GH Singleton
Abstract: In the 20th century, a
marine industry evolved to dredge sand and gravel from the
seabed around the United Kingdom, in order to provide an
alternative source of aggregates for the construction industry.
Marine sand and gravel was also dredged for beach replenishment
schemes around the UK coastline. During the latter part of
the century, there was an increased focus on coastal and marine
issues generally, by both the public and regulatory authorities.
In the context of coastal and marine resource management, this
paper reviews the recent developments that have taken place
within the marine aggregate dredging industry and discusses the
evolution of the institutional frameworks within which the
industry operates.
Entrainment Thresholds of
Naturally-shaped Fluvial and Marine Gravel (Granule) Sediments:
A Laboratory Study
H Monteith
Abstract: Using uniform beds and
unidirectional flow conditions, the entrainment thresholds of
naturally-shaped fluvial and marine gravels of granule size (2—2
mm) are determined by laboratory flume experiments.
Microscopic shape analysis shows that fluvial sediments are more
angular than beach gravels. For a given grain size,
critical bed shear stress (
to)
in fluvial sediments is 47.6% lower than that recorded
for marine gravels; efficiency of entrainment is related
primarily to shape effects, in terms of protrusion. This
difference in the bed shear stress requirement for 'threshold'
identifies the problems of adopting empirical relationships
irrespective of environmental setting.
AUV Standardisation—Report on
Workshop
I Brown
The Science of Decommissioning—Report on Conference
MJ Sayer and E Breuer
Book Review
NOAA Diving Manual: Diving for
Science and Technology (4th Edn), by Ed James T Joiner
Reviewed by J Bevan
Underwater Technology Vol 25 No 2
Summer 2002
Special Decommissioning Issue
A Personal View
The future of
exporting
K Forest
Technical Papers
Modelling the Behaviour and
Environmental Impact of Cuttings Piles During Decommissioning
AO Tyler; ZA Sabeur and MC Hockley
Abstract: A model has been
developed to predict the evolution of cuttings piles comprising
discharged drilled strata and associated additives , under
natural environmental forcing, and man-made operational
disturbances. The model uses a Lagrangian
particle-tracking technique to represent the three-dimensional
erosion and physical dispersion of particulate material.
The model is also able to represent chemical interactions and
includes an ecotoxicological risk assessment approach.
The model has been run for illustrative disturbances arising
from operational intervention on the cuttings pile and natural
conditions of tidal/residual currents and storm waves.
Despite the uncertainties in input data, the model has
demonstrated a capability to provide quantitative support to
decision-making on options for future cuttings pile management.
On-going studies are seen as contributing significantly to
the refinement of the model and its use in modelling long-term
evolution of cuttings piles.
Erosion of Cuttings Pile Sediments: A Laboratory Flume Study
KS Black, DM Paterson and IR Davidson
Abstract: The best practical option for remediation of drill
cuttings piles is directly contingent on a firm understanding of
the properties and attributes of these sediments. Whilst
there is an increasing literature on the geochemical
characteristics of cuttings piles, comparatively little is known
regarding the transport by tidal currents and waves. This
paper reports some laboratory flume experiments conducted to
ascertain the threshold entrainment shear stress (
t
crit)
of drill spoil sediments
from two locations (near to the drilling axis and outside the
rig periphery) on the NW Hutton platform.
t
crit
varies between 0.12—1.52 Nm־
and statistical analysis shows a difference in sediment
mobility wherein sediments farthest from of drilling axis are
comparatively more stable. Specialised low-temperature
scanning electron microscopy (LTSEM) and compositional analysis
of sediments (particle size, metal and organic content,
inhabitant macrobenthos) are used to provide some insight into
the differences between sites. Swelling attributable to
the greater clay content of sediment close to the drilling axis
may, in part, explain the observations. Comparison of the
measured entrainment thresholds with both tidal and wave-induced
bed stresses (separately) predicted using numerical models
indicates that the sediments are unlikely to be moved by the
prevailing tidal currents, but may be moved or agitated by
extreme winter storms (wave height ~9—10m).
However , observations made during the flume experiments suggest
a winnowing of the fine particles from the sediment matrix under
sub-threshold stress, which may be important if these particles
are geochemically reactive
Fundamentals of Drill Cuttings Pile Formation in the Sea
L Eames and D Vadnjal
Abstract: The fundamental process of contaminated pile
formation by depositing drill cuttings into the sea is
discussed. A new mathematical model of these processes is
developed and tested against small-scale laboratory experiments.
the experimental study shows how the piles are formed by the
development of a particle-laden plume descending to the sea flow
which spreads laterally, over a considerable distance, as a
particle-driven gravity current. the model predictions are
applied to interpret published field data measurements.
These results show that the thickness of drill cuttings piles
decreases rapidly with distance from the initial source of
cuttings and, that when natural biodegradation occurs, only a
smaller fraction of the pile area or mass requires treatment.
A Multicapability Sensor for Hydrocarbons, Synthetic-based
Fluids and Heavy Metals: Applications for Environmental
Monitoring During Removal of Drill Cuttings Piles
D McStay, P Robertson, P Pollard, I Edwards, E Bonsen,A. Al-Obaidi
and D Tait
Abstract: As part of any drilling cuttings pile removal
process the requirement for monitoring the release of
contaminants into the marine environment will be critical.
Traditional methods for such monitoring involve taking samples
for laboratory analysis. This process is time consuming
and only provides data on spot samples taken from a limited
number of locations and time frames. Such processes,
therefore, offer very restricted information. The need for
improved marine sensors for monitoring contaminants is
established. We report here the development and
application of a multi-capability optical sensor for the
real-time in situ monitoring of three key marine
environmental and offshore/oil parameters: hydrocarbons,
synthetic-based fluids and heavy metal concentrations. The
use of these sensors will be a useful tool for real-time in
situ environmental monitoring during the process of
decommissioning offshore structures. Multi-capability
array sensors could also provide information on the dispersion
of contamination from drill cuttings piles either while they are
in situ or during their removal.
A Novel Approach for the Study of North Sea Drill Cuttings
Accumulations: The Combined Use of an ROV and Benthic Lander for
In Situ Measurements
E Breuer, OC Peppe and GB Shimmield
Abstract: Two benthic lander systems were used as part of a
project investigating the geochemical characteristics of a North
Sea drill cuttings pile. Complications associated with
deploying sampling gear in close proximity to the platform
required an innovative technique to obtain the necessary
measurements. To achieve this goal, two deep-sea
autonomous free fall vehicles (benthic landers) were adapted for
deployment and transport by remotely operated vehicle (ROV).
The landers were fitted with a microelectrode profiling system
for obtaining high-resolution oxygen, sulphide and pH profiles,
and a rig to deploy gel proves into the sediment to examine
dissolved trace metal profiles within the cuttings pile.
The use of an ROV for deployment of the landers enabled the
simultaneous collection of data within a defined spatial context
while providing real-time visual feedback of the landers
operating on the seabed. Eight deployments were made over
5 days, totalling over 100 hours of sampling time. The
successful deployment and retrieval of the instrumentation, the
quality of data obtained and the limited disruptions to the
ongoing ship operations demonstrate the value of the lander
system as an efficient and versatile tool for in situ
biogeochemical investigations in areas associated with sampling
and measuring difficulties such as North Sea drill cuttings
piles.
The Occurrence of the Coral Lophelia pertusa and other
Conspicuous Epifauna Around an Oil Platform in the North Sea
JM Roberts
Abstract: Lophelia pertusa is a cold-water coral most
frequently reported on the shelf edge and offshore banks of the
north east Atlantic. The occurrence of this and other
conspicuous large epifauna on moorings 2 km from an oil
production platform in the North Sea were recorded from video
surveys by remotely operated vehicle. Sea anemones and
soft corals were abundant and a total of 133 colonies of L.
pertusa were observed. These occurrences and those on
the Brent Spar are the first documented reports of live
L.pertusa in the North Sea. L.pertusa was restricted
in its distribution to water >70 m, below the seasonal
thermocline in the northern North Sea. It is estimated
that coral sampled from a single point mooring had a linear
extension rate of at least 5 mm per year, a rate comparable with
existing estimates. It seems likely that these colonies
will have originated from populations along the Atlantic margin
with larvae transported into the northern North Sea in cooled
Atlantic water, possibly via the east Shetland Atlantic
Inflow current. The implications of this finding in terms
of the environmental sensitivity of this species remain unclear
since it is not known to what extent that have been exposed to
any drilling discharges. It is possible that corals have
persisted on and around oil industry installations as bottom
trawling is excluded from the installation area.
Rigs to Reefs: A Critical Evaluation of the Potential for
Reef Development Using Decommissioned Rigs
MDJ Sayer and MSP Baine
Abstract: This paper reviews the effects existing platform
and associated structures have on fish species of commercial
importance and discusses what effect the decommissioning process
could have on sold stocks in a North Sea context. The
success of the 'rigs to reefs' programme in the Gulf of Mexico
has generated some interest in adopting a similar policy on some
scale in the North Sea. How this may be achieved following
OSPAR 98/3 is reviewed. Studies on the aggregations of
fish species have estimated that less than 1.3% of North Sea
saithe stocks and less than 0.25% of North Sea cod stocks are
associated with oil and gas structures. There is evidence
to suggest that fish associated with platforms grow and taste
better than offplatform fish, even though very small elevations
in hydrocarbon contamination have been detected. Whole
ecosystem-based modelling approaches to fishery management
indicate that total protection or regeneration of stocks is
achieved only through significant area closures to the fishery.
The present area closed to the fishery is already maintaining
the North Sea fisher status quo. Converting
existing structures into offshore reefs is considered unlikely
to increase the present area of fishery exclusion nor improve
its productivity, even if it was possible under OSPAR 98/3.
There has been some speculation of a reef-dominated exclusion
zone, whereby the reefs act as a central attractive feature.
Bringing the structures inshore for reef construction may have
localised positive socio-economic impacts for coastal
communities, but achieves no financial benefit for the
production industries and does not remove any long-term
liability. Without significant levels of state support,
both in the fields of construction and liability replacement, a
programme of converting rigs into reefs will be difficult to
achieve in the context of the North Sea.
Technical Notes: Sampling and Analysing Drill Cuttings
AC Skinner; D Long and GJ Tulloch
Abstract: The scientific study of drill cuttings on and
from the seafloor requires that a number of technical challenges
be overcome. The location of the cuttings piles means that
in situ measurement and sampling methodologies often have
to be innovative in order to work around and within the platform
structure and seabed installations. In many respects,
cuttings do not behave like sediments, so traditional survey and
sampling technologies need adaptation to meet the challenges
posed by the composition. Sample handling procedures have
to accommodate health and safety considerations additional to
those normally associated with marine sampling. Novel
measurement techniques are required to analyse the material
geotechnically and geochemically both in the field and in the
laboratory. The British Geological Survey has been
involved in developing all of these aspects of cuttings pile
surveys and analyses and aspects of this work are presented in
this paper.
Decommissioning Pipelines and Subsea Equipment: Legislative
Issues and Decommissioning Processes
JM Anderson
Abstract: The Oslo/Paris (OSPAR) Commission Decision 98/3 has
placed an obligation on the UK effectively to preclude the
disposal of offshore installations at sea. Decision 98/3
has been enshrined in UK law under the Petroleum Act 1998.
However, the Decision does not apply to pipelines, and there are
no international guidelines on the long-term decommissioning of
pipelines.
The UK Government does provide some guidance on pipeline
decommissioning on the UK continental shelf, both through the
Guiding Principles, which provide the policy framework for
decommissioning decisions, and in the Guidance Notes for
Industry, which provide interpretation and guidance for
decommissioning under the Petroleum Act 1998. However,
existing guidelines are concerned with the process of pipeline
decommissioning, and the end point for these activities remains
open.
This paper considers both the legal framework and the
processes for decommissioning pipelines and subsea equipment.
Some key issues that need to be addressed are discussed.
There is still little by way of precedent for decommissioning
pipelines, partly because most major pipelines have not yet
reached the end of their economic life-span, but also because
there is a conscious desire to defer pipeline decommissioning
until the appropriate technology has been developed.
Furthermore, with little prescriptive guidance on pipelines, and
uncertainty over future OSPAR considerations, there is little
incentive for operators to face the challenges of pipeline
decommissioning directly in the near future.
Underwater Technology Vol 25 No 3
Spring 2003
A Personal View
We can rewrite the
story of 20 years of failure
J Hind
Umbilicals – Repair or Replace?
Technical Papers
Time-lapse Photography in the
Deep Sea
BJ Bett
Abstract: Time-lapse photography (TLP) has been used in
scientific applications for over 100 years, and has been used in
deep-sea operations for the last three decades. Here I
review the use of TLP in deep-sea science by reference to case
studies drawn from a 20-year history of 'Bathysnap'
(Southampton Oceanography Centre's TLP system) deployments in
North East Atlantic. Examples are given of echiuran
feeding, xenophyophore growth, benthopelagic scavengers, and
long-term studies of phytodetritus. Although the
technology for TLP will change over time, the concept remains of
great value in studying the remote deep-sea environment.
Mapping the 3D Spatial Distribution of Dissolved Manganese In
Coastal Waters Using an In Situ Analyser and the Autonomous
Underwater Vehicle Autosub
PJ Statham, DP Connelly, CR German, E Bulukin, N Millard, S
McPhail, M Pebody, J Perrett,
M Squires, P Stevenson and A Webb
Abstract: An in situ dissolved manganese (Mc)
analyser has been built and used with the autonomous underwater
vehicle (AUV) Autosub. The Mn analyser uses a continuous
flow system to produce a coloured complex with Mn in seawater,
which is measured in a flow-through detection cell. The
detection limit of the current system is 25 nmol dm -3,
and using 10-s averaged data, the along-track resolution of the
system is about 10 m. The analyser was successfully used
with Autosub in Loch Etive, Scotland, to define the
three-dimensional distribution of dissolved Mn in sub-surface
waters. This application of AUV and sensor technologies in
combination demonstrates the great power of the approach for
determining the quasi-synoptic distribution of chemical species
in environments (e.g. under ice, and horizontal space scales at
depths of up to 500km) where more conventional approaches are
not appropriate.
Development of the 'Cocoon'
Subsea Fishing Protection System
]HA Baker
Abstract: This paper describes a novel approach to protecting
fishermen from the hazards of snagging on subsea christmas
trees. It presents the background to the development, and
explains how the system works. the fishing loads and the
design philosophy are discussed. The more general
protection philosophy that follows from the design is also
presented., The system is applicable to waters of any
depth or location where bottom trawling is carried out. A
glossary is included at the end of the paper.
Technical Briefing: Energy Storage Systems for Unmanned
Underwater Vehicles
SM Abu Sharkh and G Griffiths
Introduction: The power source of an underwater vehicle is
the main component that determines its range of travel and the
tasks that it can perform. Until recently, the choice of
practical power sources for most applications has been limited
to lead―acid and silver―zinc batteries are a well-established
technology and are available at low cost. However, they
have a low energy density (
~25
Wh kg -1). Although
silver―zinc batteries have a high energy density (~120
Wh kg -1), they are very
expensive, costing 20 times the price of lead―acid.
They also have a very short life of 40―1-- cycles compared with
1000 cycles for lead―acid [1].
In recent years considerable research and
development work has been done on advanced power sources for
road electric and hybrid vehicles. This ongoing work is
motivated by environmentally driven legislation aiming at
reducing the harmful emissions of conventional internal
combustion engine vehicles (e.g. [2, 41]).
The power source should ideally have a
high energy density, high power density (higher charge and
discharge rates), low cost, long life, low maintenance, high
efficiency and wide operating-temperature range. It should
also be safe and recyclable. In addition to these
requirements, which are similar to those for a road vehicle,
there are additional considerations imposed by working in the
underwater environment. Ideally, the power source should
be non-gassing and, in the case of batteries, the electrolyte
should be spill-proof. the operation of the power source
should be independent of depth.
This paper presents a review of the
features of different types of batteries (primary and secondary)
and fuel cells that have been used in autonomous underwater
vehicles (AUVs), highlighting their merits and operational and
engineering issues that need to be considered when using them.
It also presents a survey of potentially promising alternative
types of batteries and energy-storage systems including flywheel
electromechanical batteries and supercapacitors.
Meeting Reports: Maritime World 2025: Future Challenges and
Opportunities
INL GalIett
West Africa - The Oceanographic and Meteorological Conditions
and their Challenges to the Oil and Gas Industry
INL Gallett
Book Reviews
The Diving Manual: An
Introduction to Scuba Diving, by D Ellerby
Reviewed by J Bevan
Climate of UK Waters at the Millennium: Status and
Trends, Editors G Alcock and L Rickards
Reviewed by WJ Gould
Waves in Ocean Engineering, by MJ Tucker and EG Pitt
D Faulkner
Underwater Technology Vol 25 No 4
Winter 2003
A Personal View
Shortage of scientists
and engineers for the offshore industries
I Gallett
Technical Papers
Reliability Capability
Evaluation and Improvement Strategies for Subsea Equipment
Suppliers
K Williams, N Robertson, C Roberts Haritonov and J Strutt
Abstract: This paper presents the approach that BP and Boreas
Consultants have taken to evaluate reliability capability and
how this has been used to implement workable strategies to
improve reliability in subsea equipment supplier federal
contracts. Key findings, lessons learned and strategy
elements from this process are presented.
The paper will conclude with recommendations on how key
elements of this strategy and the lessons learned from
implementing it within federal contracts can be built upon to
improve reliability capability throughout the subsea industry.
The application of reliability principles as the industry moves
into the more dynamic environment of deepwater project
specification and execution is specifically addressed.
On the Reliability of the Autosub Autonomous Underwater
Vehicle
G Griffiths, NW Millard, SD McPhail, P Stevenson and PG
Challenor
Abstract: As autonomous underwater vehicles (AUVs) enter
operational service, an assessment of their reliability is
timely. Using the Autosub AUV as an example, several
design issues affecting reliability are discussed, followed by
an analysis of recorded faults. Perhaps contrary to
expectations, failures rarely involved the autonomous nature of
the vehicle. Rather, faults were typical of those that
occur with any complex item of marine electromechanical
equipment. Reliability under various operating conditions
was assessed using Weibull parametric models. This
reliability modelling was extended to the case of a vehicle
operating under ice in order to estimate the probability of loss
in situations where the support vessel could not gain access to
a malfunctioning vehicle.
Retrieval of an Autonomous Underwater Vehicle: An
Interception Approach
SM Ahmad, R Sutton and RS Burns
Abstract: Guidance and navigation of airborne missiles has
been reported extensively in the literature; however, little
attention has been paid to the issue of guidance and docking of
an autonomous underwater vehicle (AUV). The retrieval of
an AUV to a mother submarine (target) is conceived as a target
interception problem and is considered herein. The design
problem is solved in two stages: first, the guidance technique
is demonstrated assuming zero lag AUV dynamics; next, the
AUV-controller dynamics is included in the guidance loop.
Thus, the issue of guidance, navigation and control is solved in
a unified framework. This is necessary for a realistic
evaluation of the AUV-target engagement geometries.
Finally, the effectiveness of the guidance scheme in presence of
disturbances is also illustrated.
Properties of Photopolymerisable Acrylic Adhesives for
Underwater Bonding
PI Dolez, C Williams, A Goff and B. Love
Abstract: The bonding properties of two photopolymerisable
acrylic adhesive formulations have been measured in terms of
bonding strength in pure shear, which ranges between 2 and 6
MPa. These resin systems have been developed ultimately
for marine applications and have been designed to address very
demanding requirements: underwater bonding in a very short time
(less than a minute); at low temperatures (as low as 1°C); and
on a wide range of marine surfaces. The bonding strength
dependence on curing time, curing temperature, substrate
roughness and material for the two resin systems demonstrated
their potential as marine adhesives. Measurements of their
shelf-life behaviour at various temperatures and of the water
ageing of bonds are also reported.
Meeting Reports:
Emergency Recompression:
Co-ordinating the Need…Revisited
J Bevan
Introduction: The meeting was opened by the Chairman, David
Elliott, Independent Consultant in Diving Medicine, and then the
scheme was set by Martin Sayer of the Dunstaffnage Hyperbaric
Unit, Oban. As both a provider of emergency recompression
treatment and a 'diving contractor', Martin Sayer was in a good
position to offer an overall view. He provided a brief and
objective introduction to the several important issues the
meeting would address. Interestingly, he pointed out that
for every one recompression treatment of an inland/inshore
professional diver (or any other type of professional diver),
the Dunstaffnage unit would treat some 30 recreational divers
(including so-called 'quasi-professional' inland/inshore
divers). In terms of numbers of treatments, it was very
clear that the recreational divers were the main source of
patients.
Monitoring and Measuring the Underwater Environment
IG Priede
West of Shetland Drilling Operations – Validating Riser VIV
Fatigue Life Predictions
G Jeans
Book Reviews
Klinger's Diving Machine,
Editors M Fardell and N Phillips
Reviewed by J Bevan
Ocean Waves and Oscillating Systems: Linear Interactions
Including Wave Energy Extraction, by J Falnes
Reviewed by D Faulkner
