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The Virtual Control Buoy –A New Application For Solar-Powered AUVs

Kevin Mullen

SUT Annual Conference 2009, Perth, Western Australia

The squiggly line in the graphic – what’s it all about? I’ll explain this later in the

presentation.

To set the scene, Western Australia is blessed with a number of very large gas

fields.

Unfortunately, they are subsea, and they are generally remote from land.

To control them, you need either long distance umbilicals, or control buoys, or

platforms or floating facilities, but all of these have disadvantages.

As an alternative, I’m proposing something called the Virtual Control Buoy to provide a means of communicating from the onshore control facility to the subsea

wells.

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The Virtual Control Buoy –A New Application For Solar-Powered AUVs

Kevin Mullen

SUT Annual Conference 2009, Perth, Western Australia

I presented one realisation of the VCB, using seagliders, at the DOT Conference in December.

I’m very grateful to the SUT committee, and specifically Chris Lawlor, for their invitation to talk about the VCB at this conference.

Much of the material I’m presenting here is new, as it deals with another type of

AUV called the Solar-powered AUV.

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� Long Distance Umbilicals

• Cost

• Reliability

• Transportation and Installation

� Control Buoys

• Reliability

• Operations

• Logistics

• Personnel Access

Difficulties perceived by clients

Conventional methods of controlling remote gas fields require control by either long distance umbilicals, or control buoys, or of course platforms or floating

facilities.

All these conventional methods have disadvantages:

• Long distance umbilicals are expensive to purchase, are expensive and

inconvenient to install, may experience hydraulic or electrical failure, and are prone to damage by trawling or anchor damage;

• Control buoys are inexpensive, but they can be perceived by clients as having operational problems for maintenance, bunkering with diesel fuel or

chemicals, or getting men on and off them; and

• Platforms and floating facilities are expensive, and may require a large

team to operate them.

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Another Solution

� Another method of controlling remote wells –

� The Virtual Control Buoy

• Eliminates umbilicals

• Fault tolerant

• Robust

• Cheaper than control buoys

• Works at any stepout

• Reduced maintenance of remote control facilities

I’m proposing another solution, called the Virtual Control Buoy, as an alternative method of controlling remote wells.

I claim that it has all of the advantages listed here, and that it eliminates the difficulties associated with the operation and maintenance of remote facilities or

umbilical systems.

So what is the Virtual Control Buoy?

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� Two or three AUVs drift above each wellhead

� AUVs perform control and communications

The Virtual Control Buoy

The VCB concept uses Autonomous Underwater Vehicles (AUVs), as a means of communicating from the onshore control facility to the subsea wells.

Here I’m showing a seaglider.

A fleet of two or three AUVs drift above each subsea wellhead, communicating

with the wellhead by acoustics, and with the onshore control facility by Low Earth

Orbit satellite.

Each glider uses GPS to track its position, and if it drifts off location, it

autonomously submerges, and glides underwater, re-emerging on location.

As the umbilical is eliminated, the wellheads would be self-powered, using one of

numerous technologies proposed and trialled over the years.

Mission duration for each subsea glider would be 6-12 months, and they could be

launched and retrieved from shallow water close to the onshore base, gliding out

to the field, and returning at the end of mission for maintenance.

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Autonomous Functions

• Robust, fault tolerant • Sea gliders maintain position around the wellhead• Use several sea gliders over each wellhead

S ate l l ite

The seagliders drift above the wellhead, occasionally diving and re-establishing their position if they have drifted too far away.

communicates with the subsea wellhead by acoustics, and with the onshore

control facility by LEO satellite.

Using acoustic transmission with seagliders is already proven. Webb Research

report that in February 2003, three Slocum seagliders equipped with acoustic

modems were flown continuously for a week acting as mobile communication

gateways for sensor nodes on the seabed. Command and control was handled

acoustically and then relayed via radio modem and Iridium satellite modem.

Acoustic control of well is already proven – not from seagliders, but from a

platform. This was demonstrated by the Agip Luna project in 1996.

Satellite communication is preferred for communications from land to an

offshore seaglider. The preferred means of satellite communication is LEO

satellite link (e.g. Iridium and Globalstar networks), which is well suited for the limited data and the transfer rates required. Messaging systems such as the

Iridium Short Burst Data (SBD) service can provide cheap bidirectional transfer of

information.

Due to the low orbit height of LEO satellites, simple low power transmitters are

adequate, with antennae that do not require pointing.

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AUVs – spoilt for choice

But there are other types of AUV.

Decisions, decisions…

Let’s chose this one!

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� The Solar-powered AUV (SAUV) can also carry out the

control and communications function

The Solar-powered AUV

The first generation of Solar-powered AUVs was designed in 1998, by various institutes including the Russian Academy of Sciences.

This is the second-generation SAUV .

It uses solar energy to recharge its lithium ion batteries during daylight hours.

This concept offers a paradigm shift for coastal surveillance by providing an

ocean survey tool that is both autonomous and mobile with virtually unlimited

endurance [2].

SAUV II is 2.3 m long, 1.1 m wide, and 0.5 m high; its topside solar panel is 1 m2;

and its overall weight in air is 200 kg. Because of it relatively small size, the

SAUV II is easy to deploy and operate: it can be launched from a boat ramp on shore and can independently swim to a predetermined area of interest. SAUV II

can be pre-programmed before the mission, or it can have the program changed

during the mission via radio frequency (RF) communication or Iridium satellite

phone. The mission planner is a Windows-based graphical use- interface (GUI)

that renders intuitive programming and mission viewing. The mission controller is based on a PC-104 embedded single-board processor that is capable of

interpreting high-level commands to direct the vehicle’s behavior during the

mission.

The SAUV II is made of a fiberglass composite material capable of operating in

depths up 500 meters. A vectored thruster provides directional control at 1 to 3

knots, depending on mission parameters. Vehicle status and performance data

are relayed to the operator by an acoustic modem where they are logged and

displayed on the mission planner laptop

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Communications and Control

S ate l l ite

Shore communication via Low Earth Orbit

satellite, e.g. Iridium

Onshore Control Facility

• Autonomous functions in solar-powered AUVs• Autonomous functions in well

• Acoustic communications with well• Satellite communications with shore

By locating perhaps three seagliders above each wellhead, there is a high level of redundancy. If the seaglider on an adjacent well fails, or it has to come home for

new batteries, one of the seagliders on the first well can be reassigned to the

second well.

The VCB concept relies on autonomous operation in several areas:

• Autonomous position keeping by the seaglider; (refer to later slide)

• Autonomous shutdown of the subsea wellhead on loss of signal; and

• Cooperative Seaglider Behaviour.

Safe operation of the subsea wellhead relies on being able to close the wellhead

when required to stop the flow of hydrocarbons. Normally this is achieved from

the onshore plant by communication through the seaglider. You may not be able

to do this, because;

• The seaglider may have failed; or

• The seaglider may be unavailable due to adverse weather, or having all

seagliders submerged together (cooperative behaviour is needed); or

• The satellite communications may have broken down (satellite fault, or

space or terrestrial weather conditions).

To be fail-safe, the subsea wellhead needs to shut itself in after say 15 minutes of

loss of comms. While this may seem excessively long, it is not a concern

because the export pipeline already contains a very large inventory, which only

increases slightly during this 15 minute period.

Redundancy of the Iridium satellite equipment should be provided, and also

diversity should be provided in utilising equipment for a second satellite constellation e.g. Globalstar. This combination of redundancy and diversity will

give a high level of availability.

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The Solar-powered AUV

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The Solar-powered AUV

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Hardware, Software, Theory

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Software Architecture

http://ausi.org/publications/SAUVIIHighLevel.pdf

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Virtual Moorings

� Each AUV uses GPS to track its position

� If it drifts outside its watch circle –

• it autonomously directs itself to an upstream position

• and continues within the watch circle

As long as currents are not stronger than glider speed, a glider can be programmed to perform repeated dive profiles while holding its location nearly

constant. In this mode of operation, which has come to be known as the "virtual

mooring", a glider can hold station as well as the surface buoy of a mooring, on

the order of 1 km. A glider may be deployed to transit to a predetermined

location, virtually moor itself for a time, and later return to be picked up close to shore.

The formation behaviour of the seagliders in a cluster should be controlled in such a way that only one of the seagliders is engaged in a dive at any one time.

Extensive academic research and trials have been carried out on multi-AUV

cooperative control of fleets of autonomous underwater gliders, and it is expected

that this issue can be solved in a satisfactory manner. There is also the prospect

of the academic community accepting this challenge, and carrying out the research and development required by industry.

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Virtual Moorings

One Seaglider (track in red) remained near a target about 2

miles north of a surface mooring

(buoy positions shown in cyan)

Scripps Institution of Oceanography

1999 experimentTracks of Spray seagliders in Monterey

Bay (depth contours in meters).

Conventional moored metocean buoy

Sea glider in Virtual Mooring mode

In an early demonstration of glider performance in 2000, a Spray seaglider was virtually moored in an underwater canyon off Monterey.

The seaglider was commanded to a target about 3.5 km north of the anchor position of a surface mooring maintained by the Monterey Bay Aquarium

Research Institute.

A tight cluster of surface positions (red symbols) demonstrated that this virtually moored glider held position at least as well as the moored surface buoy (cyan

symbols).

This shows how the seagliders behave in the field, but how do we get them out to

the field?

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Sea Glider Transiting to Field

The seagliders can be launched in shallow water close to the onshore base from small boats, and they make their own way out to the field. At the end of mission,

they are instructed to come back to shallow water for recovery.

Launch and recovery takes place close to shore, where the sea state is more

benign than out in the open ocean.

Launch and recovery times can be programmed during periods forecast to be calm, with a low seastate.

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� No umbilical

� Self-powered

� Autonomous

Self-Powered Wellheads

A final piece in the jigsaw puzzle is the other things that umbilicals supply –electrical and hydraulic power.

Generation of electrical power is needed to operate the control and communication systems at the wellhead, and also to operate pumps to generate

hydraulic power for the operation of valves in the subsea xmas tree and

downhole.

Numerous methods exist for subsea power generation:

• Kvaerner SPARCS (Subsea Powered Autonomous Control System) 1994;

• ABB SWAT (Self-powered Wellhead with Acoustic Telemetry) 1985;

• Caltec MURCS (Minimum Umbilical Remote Control System) 1998;

• Agip SWACS (Autonomous Control System for a Subsea Well), 1996; and

• Concept for Turbine Generator powered by the MEG line, Martyn Witton, 2003.

At present, the major manufacturers have mothballed the technology, and only Weatherford is progressing it with a design for a Subsea Hydraulic Power Unit.

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Subsea HPU

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Satellite Communications

� Low Earth Orbit (LEO) Satellite Link

• Constellations of low altitude satellites

• Globalstar, Iridium and Orbcomm

• Antennae do not require pointing

• Low power equipment

• Low cost equipment

• Messaging services

• Already well-proven with seagliders and SAUVs

� Damage to Iridium satellite

Satellite communication is preferred for communications from land to an offshore seaglider. The preferred means of satellite communication is LEO

satellite link (e.g. Iridium and Globalstar networks), which is well suited for the

limited data and the transfer rates required. Messaging systems such as the

Iridium Short Burst Data (SBD) service can provide cheap bidirectional transfer of

information.

Due to the low orbit height of LEO satellites, simple low power transmitters are

adequate, with antennae that do not require pointing.

The next time you wish upon a falling star, it might just be part of your subsea

control system burning up in the atmosphere.

According to some experts, this Feb. 10 incident, the first known collision

between two fully intact satellites - Iridium 33 and Russia's spent Cosmos 2251

communications craft

According to a Feb. 11 e-mail alert issued by NASA, Russia's 1,984-pound (900-

kg) Cosmos 2251 -launched in 1993 but out of service since 1995 - collided with

the 1,234-pound (560-kg) Iridium craft at 11:55 a.m. EST at an altitude of 490 miles (790 km). Bethesda, Md.-based Iridium Satellite LLC alerted the U.S. Air

Force after losing contact with the Iridium 33

In a statement issued to media Feb. 11, Iridium said it would move one of its in-

orbit satellites within 30 days to permanently replace the lost satellite. The

company announced Feb. 13 that it had completed a "service hole patch" as a

stopgap measure against limited services disruptions resulting from the loss of

the satellite.

Iridium, the Bethesda-based satellite services company, had 66 working satellites

in its "constellation" as of Tuesday morning, plus eight spares, company spokeswoman Liz DeCastro said.

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Acoustic Communication

� Acoustic communication from an SAUV

• using a Benthos MODEM

• good for up to 2 km through the water

• 800 bytes per second

� Agip SWACS project (subsea wells acoustic control system)

• installation in 1987 on the Agip Luna 27, in the Ionian Sea.

• The well was located in 176 meters water depth

• 3,700 meters away from the Luna A platform

• Still producing in 1996

Graphic courtesy of SPE 36940

Acoustic communication from an SAUV using a Benthos MODEM is good for up to 2 km through the water at about 800 bytes per second.

Using acoustic transmission with seagliders is already proven. Webb Research

report that in February 2003, three Slocum seagliders equipped with acoustic

modems were flown continuously for a week acting as mobile communication gateways for sensor nodes on the seabed. Command and control was handled

acoustically and then relayed via radio modem and Iridium satellite modem.

Acoustic control of well is already proven – not from seagliders, but from a

platform. This was demonstrated by the Agip Luna project in 1996.

SWACS project: A research and development project named subsea wells

acoustic control system (SWACS), was carried out with Tecnomare and Kongsberg as main contractors. The system can control and monitor up to 15

wells in water depths up to 1000 meters. No umbilicals to the surface are

required, either for electric lines or for hydraulic ones.

The system relies on an autonomous energy source for power supply and on

acoustic link for signal transmission. Following extensive dry tests of all the

components and of the assembled prototype, a successful installation of the

system's first prototype took place in the summer of 1987 on an Agip live well, the Luna 27, in the Ionian Sea. The well was located in 176 meters water depth, and

3,700 meters away from the Luna A platform.

Agip SWACS (Subsea Wells Autonomous Control System) project (Fig. 1). This project commenced in 1982 and culminated in the installation of a SWACS

prototype on the Luna 27 gas well, located offshore Crotone at a distance of 4 km

from the Luna A platform, in December of 1987.

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Mission Duration

� Sea gliders glide out to the field. . .

• . . . and return at end of mission for maintenance

• Thermal gliders generate their own power

� Potentially 6-12 months for thermal gliders

� Solar-powered AUVs

� Potentially 12 months for SAUVs

This is the vision, of mission durations for the seagliders of 6-12 months. I have a researcher at the University of Western Australia who is looking at

power/energy/duration issues right now, as his Master’s thesis.

The enabling technology for long mission durations is harvesting the energy

needed for the propulsion from the ocean's temperature gradient. The ocean is

warm at the top and cold in deeper water.

Thermal propulsion uses the volume change that occurs when melting a

substance like wax. In warm water at the surface the wax melts, and expands. As

the glider dives into cold deep water, the wax freezes and contracts.

At the surface, the expanding wax converts heat to mechanical energy. This

stored mechanical energy is used to push oil from a bladder inside the vehicle’s

hull to one outside, changing its buoyancy and initiating the dive. At the bottom of

the dive, the wax cools and the cycle reverses. It’s not actually perpetual motion, because it uses the thermal gradient in the ocean – it only seems like perpetual

motion.

In April 2008, a research team led by Dave Fratantoni of Woods Hole

Oceanographic Institution (WHOI) retrieved a prototype thermal glider that they

had launched 4 months before in the Caribbean Sea. The vehicle had

crisscrossed a deep ocean basin 75 times, travelling more than 3,000 km.

Dave Fratantoni said "We now believe the technology is stable enough to be

used for science. It is no longer just an engineering prototype".

The net result of using thermal propulsion is that all the electrical energy in the

seaglider's batteries can be used exclusively for control and communication.

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Practical Issues with Solar-powered AUVs

� Biofouling� Launch

Seagliders are small and light enough to be handled by two men, and can readily be launched from small vessels. The seaglider sails out to the field, and then

returns at the end of the mission for retrieval and maintenance.

The mission duration for thermal seagliders is potentially 6-12 months, so the

work involved in maintaining the seaglider fleet is not excessive

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Things that the VCB can’t do

� Chemical Injection –

• needs chemical injection lines from shore/surface

� Annulus venting –

• inject annulus pressure into production side

� Hydrate remediation –

• other provision need to be made

I’ve already pointed out that seagliders are not suitable for all applications.

There are also some things that an umbilical can do, which a seaglider can’t.

Consider these requirements, which are often fulfilled using umbilicals.

Chemical injection for example, for injecting MEG or methanol into gas wells. For

long distance delivery systems, hydrate inhibitors are better delivered through

coiled tubing strapped to the flowline, rather than using lines within the umbilical.

This is on the basis of cost, and on the basis of the umbilical size and the shear

volume that has to be stored on the carousel vessel.

The apparent disadvantage of needing to deliver chemicals may actually be used

to advantage, to generate power subsea. Martyn Witton told me in 2003 of a concept for a turbine generator powered by the MEG line (for a project unrelated

to seagliders).

If you strap a second coiled tubing to the flowline, you can remediate hydrate

blockages – though it always better to stop them happening, rather than trying to

fix them afterwards.

For annulus venting, you may be able to squirt it into the production side.

Alternatively, if you’ve got a second coiled tube to allow for hydrate remediation,

you can use that for annulus venting.

One potential showstopper may be the need to inject other chemicals, perhaps

corrosion inhibitors. I’m not sure if I’ve got an answer for that. As I pointed out,

the VCB is not suitable for all applications.

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Reasons for not using the VCB

� Damage by passing vessels

� Negotiating shipping lanes in transit

� Theft or "Salvage" by passing vessels

� Ice

� Areas with constant currents > 3 m/s

� Conservative attitude of oil and gas companies

We identified a number of reasons for not using Virtual Control Buoys.

The seagliders may not work well in busy shipping lanes. They have also been

known to be “salvaged” by passing vessels. I’ve heard of one that being tracked and its velocity suddenly went from half a metre per second to about 12 knots

towards shore. Not only that but it actually travelled further inland. The owners

eventually located the seaglider in a fisherman’s garage – he’d taken his little

yellow trophy home with him!

The seaglider may also struggle in areas with high currents, or in ice, or in

shallow water which is too shallow for diving or for the temperature differential

needed for the thermal gliders.

None of these problems apply off the North West Shelf of Australia. It’s a dream

location for the Virtual Control Buoy - deepwater, remote, very little infrastructure.

The biggest problem facing this concept is not the little yellow things – it’s the oil

and gas companies, and their pre-occupation with BYTs – Big Yellow Things.

They like their infrastructure to stay in one place, preferably piled in position. Having their comms link to the wells floating about, at the mercy of wind and

waves, may be a step too far for them.

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Feasibility

� All the technologies proposed are established:

• Sea gliders / Solar-powered AUVs

• Virtual moorings

• LEO satellite communications

• Subsea acoustic communications

• Self–powered autonomous wellheads

� The only novel aspect is using AUVs for control

This concept uses a number of existing proven technologies in a new way which could provide technical and economic benefits for the remote control of the large

gas developments off the North West Shelf of Australia.

All the technologies are proven, the only new thing is using them all together, and

using them for control of subsea wellheads

The technique is also being launched into industry with no strings attached to it. There are – deliberately - no patents or licenses on this.

The claim is for control of subsea facilities using any autonomous vehicle. This

concept is released – free of patents – for the subsea community to use.

Hydrocarbon sniffer

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Maturity of the technology

� Two contrasting opinions:

• “AUV technology has evolved over the past 10 years to a

point where the technology is relatively stable and has

been accepted as a viable method for many underwater

applications” - U.S. Commission on Ocean Policy, “An

ocean blueprint for the 21st century”, 2004.

• “Damn, damn, damn!”

AUV technology has evolved over the past 15 years to a point where the technology is relatively stable and has been accepted as a viable method for

many underwater applications http://ausi.org/publications/SAUV_30DayTest.pdf

U.S. Commission on Ocean Policy, “An ocean blueprint for the 21st century, final

report,” Washington D.C., ISBN# 0-9759462-0-X, 2004.

There is a saying among folks who work with AUVs: They will start any interview

by saying, “Damn, damn, damn!” Scott Pegau of the Oil Spill Recovery Institute in

Cordova, Alaska, doesn’t begin this way; instead he postpones our interview altogether so he can spend some time troubleshooting his twelve-foot AUV, the

Bluefin. http://auvac.org/resources/operations/

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A Seaglider lost in action

RU17 was deployed on May 21, 2008 and was within 20 km of the Azores EEZ line when we lost communications on October 28, 2008. The Rutgers

students, technical staff and scientists flew RU17 a record breaking

distance of 5,700.59 km. We spent 160 days at sea, which translates to

22 weeks and 6 days, or 5 months and 1 week depending on your

preferred measure of time. There is no Guinness Book for glider statistics, so we have to rely on the public websites we can find. Based on that

search, it looks like we share the duration/distance records with our

friends at the University of Washington. Glider RU17 now holds the world

record for the longest distance mission for an autonomous underwater

glider – 5,700 km. A University of Washington Seaglider holds the world record for the longest duration mission – 7 months.

The most interesting scientific discovery of this mission has been the interaction of the glider with the upper ocean biological communities of the

central North Atlantic. After leaving the Gulf Stream region and heading

east of the Grand Banks of Newfoundland, we noted a decrease in glider

speed on both upcasts and downcasts, resulting in fewer undulations per

6 hour segment. The suspected cause is biofouling, since the speed decrease was slow and steady for a period of about a month before it

leveled off at a slower but steady speed.

The new discovery for us was the difference in the day-night behavior of

the upcasts and downcasts. The upcasts were sensitive to the day night

cycle, downcasts were not. There were many times when the upcast

speed at night was much slower than the upcast speed during the day. Many times at night we would have trouble making it to the top of an

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� Kevin Mullen

� INTECSEA

� kevin.mullen@intecsea.com

� http://www.intecsea.com

Contact information

"The best way to predict the future is to create it."

Peter Drucker

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It’s tough work, but somebody has to do it.

Field testing a thermal seaglider in the Bahamas.

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Subsea History

Shell UMC 1982• Underwater Manifold Centre

• "a viable subsea production system"