UT3 Issue 4 Corer ONE A copy

In order for engineers to

determine if the sea bed is strong

enough to withstand the weight

of any structure imposed upon it,

the operator will often

commission a geophysical survey,

often followed by conducting

geotechnical investigations.

This survey will examine

parameters such as soil strength,

permeability and consolidation,

thermal conductivity and

liquefaction potential to identify

strata changes, clarify apparent

anomalies or investigate seabed

features in specific areas.

There are two types of

geotechnical test.

SEABED

CORING

Coring analysis is not restricted

to geological geotechnical

engineering studies. It can also

be used in old gas exploration

to assess the geology of the

reservoir and caprock as well as

for mineral exploration.

It can be used for environmental

and climate research where the

sediment layers can record

evidence for climate changes or

the presence of heavy metals,

pollutants or micro plastics.

Additionally, It can be used in

archaeology to reconstruct

paleoenvironments and date

discover buried artefacts.

In situ analysis typically involves

pushing probes either in the

seabed or downhole in an

attempt to reproduce the

behaviour of a structure

under stress. These may be

coupled by taking samples

for subsequent analysis in

the laboratory.

A number of techniques

exist - taking samples or

cores from the seabed

or downhole. The

optimum technique

largely depends on

water depth and soil

hardness.

BOX CORERS

One of the

most

simplistic

tools is the

box corer. This

seabed

sampling

A OSIL box corer

CORING

device designed to collect an

undisturbed block of sediment,

possibly including the sediment-

water interface.

The device is lowered to the

seafloor on a wire, where it sinks

into the sediment under its own

weight.

As the box is lifted back up, a

double shovel, gate or blade

swings across to shut the

aperture, sealing the base and

trapping the sample inside.

This preserves any natural

layering and is suitable for

capturing fragile surface

sediments that other

coring methods often

disturb or wash away.

Maintaining the quality

and integrity of the

sample is its main

advantage.

SEABED CORING

enquiries@rototech.sg

www.rototech.sg

INNOVATIVE ROBOTICS

GROUND BREAKING DESIGN

• The Roto Climber Assessor Mini offers multiple

inspection choices with four high quality cameras

• Cleaning: can be equipped with either

Caviblaster or UHP water cleaning systems

• Inspection: can be equipped with Spot UT,

Pulsed Eddy Current or Phased Array UT

• Visual: equipped with four DWE Explorer HD 2.0

(four units simultaneous stream) each with

a resolution of 1920 x 1080 pixels

Introducing the Roto Climber Assessor Mini, our smallest and most lightweight device

for cleaning and inspecting smaller sizes of pipe from 6” to 12” in diameter

• Lightweight and compact

• Battery powered

• Small crew better HSE

• Minimal platform footprint

• No vessel needed

• Easy mobilisation

• 6 to 25 times cheaper than

traditional methods

• Less carbon intensive

Typically, Box corers typically retrieve samples

around 30 –50cms deep and around 50cms wide,

especially at the surface although they are often

quoted as areas. Typical units vary from 0.05m2,

through a standard 0.1m2 tp the largest 0.5m2.

The box coring technique, however, is limited by its

penetration depth.

GRAB SAMPLERS

A similar device is the Grab Sampler. This is also

used to extract a section of seabed sediment.

A pair of open jaws are lowered through the water.

When the sampler impacts on the the bottom, a

trigger mechanism closes the jaws, trapping

sediment inside. It recovers a smaller, irregular

volume than the box corer - usually just the upper

few centimetres of the seabed.

There are a wide range of different grab samplers

available, each with differing closure mechanisms.

The most commonly used grabs are the Van Veen

Grab (available in single or double bucket options),

Smith McIntyre Grab, and Offset Day Grab.

The downside is that the sediment is disturbed

because in the act of closure, the jaws can mix the

material and the layering is immediately lost. These

grabs are useful, however, in obtaining bulk material

for chemical analysis or bulk sampling of benthic

organisms, sediments, or pollutants where layering is

irrelevant.

Box corers are heavier, more complex that grab

samplers, and require winches and sturdy ship gear.

The lighter Grab Samplers can be deployed from

smaller vessels.

GRAVITY CORER

Gravity corers are free-fall sediment sampling

devices that rely on its heavy weight to drive a core

barrel into the seabed. Weight is provided by steel

or lead. Depending on the handling capacity of the

vessel, the total weight can range from 200kg up to

1,500kg for heavy-duty deep-water systems.

Grab samplers.

Above: Smith

McIntyre

Below: Van Veen

Image OSIL

SEABED CORING

Gravity corer

Underneath this weight assembly,

lies the steel core barrel, a tube,

that can measure anything up to

12m. It usually has an outer

diameter in the range of 70 to 140

mm.

Inside the barrel sits the

removable core liner, usually

fabricated of transparent PVC or

polycarbonate. This typically has a

inner diameter of 90 mm. This

receives and preserves the

sediment sample.

“Our Gravity Corers also include a

non-return valve at the top of the

core barrel string, that helps to

maintain sample integrity by

reducing sample slump in a

similar mechanism to the Piston

Corers,” said OSIL Managing

Director, Dr Richard Williams..

At the base of the liner is the core

catcher, a device consisting of

spring-steel fingers or flaps. The

catcher opens during penetration

to allow sediment into the tube

and closes as the corer is

retrieved, preventing sample loss.

At the top of the assembly is a

cap or release mechanism, which

provides attachment to the wire

rope used for deployment.

In operation, the corer is

suspended from a winch and

lowered vertically from the vessel.

Upon engagement, the unit is.

allowed to free-fall the final 5–

10m to maximise penetration

velocity.

When it strikes the seabed, the

weight forces the barrel into the

sediment.

The penetration depth is

determined by its weight, the

barrel length, and the shear

strength of the seabed material.

The recovered core length

usually ranges from 1-6m,

depending on the barrel length,

the total system mass, and the

resistance of the seabed

material.

The advantage of the gravity

cover is its simplicity, robustness,

and low cost. Apart from the

catcher, there are no moving

parts and it can be deployed

from almost any vessel equipped

with a suitable winch and A-

frame or crane.

In soft clays, such a system can

penetrate with an 80-95%

recovery ratio. It does, however,

performs more poorly in coarse

sands, gravels, stiff clays, or

cemented layers where

penetration is limited.

Even in favourable conditions,

the free-fall impact can compress

softer sediments, which can

distort the stratigraphy and affect

the accuracy of depth

measurements.

PISTON CORER

The piston corer is an

advancement of the gravity

corer concept with the addition

of an internal piston that

reduces friction and core

disturbance.

This modification allows for

much greater penetration

depths and higher-quality

samples than are achievable

with a standard gravity corer.

Piston corers are routinely used

where long stratigraphic records

or deep samples are required.

Above the barrel, a large weight

assembly provides the necessary

force to drive the tube into the

seabed. The steel core barrel is

often much longer than that of a

gravity corer. Inside the plastic

liner retains the sediment

sample.

At the upper end of the barrel

sits the piston, which is held in

place by a wire connected to the

vessel.

Because of the long barrel

lengths and the need for

controlled release, piston corers

are deployed with a dedicated

trigger mechanism.

This device ensures the corer is

released at the correct height

above the seabed, allowing for

maximum free-fall velocity

without premature penetration.

Operationally, the corer is lowered from the vessel

to just above the seabed. At a predetermined

height, the trigger mechanism releases the corer,

allowing it to free-fall under its own weight.

Upon impact, the barrel penetrates the sediment.

The piston does not move with the barrel during

penetration but instead remains fixed at the

sediment surface relative to the seabed.

This stationary piston creates a

and the suction effect draws sediment smoothly,

minimising friction. As a result, sediment enters the

liner with less compression and disturbance

compared to a gravity corer.

This significantly improves recovery efficiency and

sample quality. Penetration of 20-30m are common

in soft clays and silts,

The piston corer offers several advantages. It can

recover much longer cores than gravity corers,

often with minimal compression and good

preservation of sedimentary layering. It is therefore

the preferred tool for reconstructing long-term

paleoenvironmental and climatic records.

In geotechnical applications, it provides engineers

with long, continuous samples for strength testing

and stratigraphic analysis. However, piston corers

are mechanically more complex, require more deck

space, and demand vessels with advanced

handling systems capable of supporting long,

heavy barrels.

Deployment and recovery operations are slower

and more logistically demanding than for simpler

systems.

Despite these challenges, the piston corer remains

the most effective non-rotary system for recovering

long, high-quality sediment cores from the seabed.

It has been a cornerstone of large-scale

oceanographic programs, and continues to be

used extensively in both scientific and commercial

offshore operations.

SEABED CORING

Piston corer

Image: OSIL

Vibrocorer

Image: OSIL

VIBROCORERS

A Vibrocorer is based on

a corrosion resistant

cylindrical core barrel,

which houses the sample

during collection. The

core barrel diameters

generally range from 96

mm to 106 mm, and

lengths varying from 2–

12m.

At the base of the barrel

is the vibratory assembly,

usually comprising an

eccentric motor or

electromagnetic actuator

that generates high-

frequency, low-amplitude

vibrations.

These vibrations reduce

friction between the

sediment and the coring

barrel, allowing the

device to penetrate

dense or cohesive sediments

with minimal disturbance to the

stratification and physical

properties of the collected

material.

The upper section of the

Vibrocorer often includes a

guide frame and deployment

system, which can be mounted

on a vessel or platform, allowing

precise vertical insertion.

The vibration unit typically

produces a vibration force of 30

kN, 30 kN at 28 Hz. These forces

are sufficient to penetrate dense

or cohesive sediments, such as

stiff clays or compact sands, with

minimal disturbance to the

stratigraphy

The maximum operational

depth of the Vibrocorer is

contingent upon the specific

model and design features, but

standard models are typically

rated for depths up to 200m,

with some high-end models

capable of operating at depths

up to 600 m when equipped

with pressure-compensated

system

Vibrocorers are particularly

effective in soft clays, silts, and

fine sands where conventional

gravity or piston coring methods

struggle to achieve adequate

penetration or preserve

sediment structure.

The operational parameters,

such as vibration frequency,

amplitude, and penetration rate,

are carefully controlled to

optimise core recovery while

minimising sample disturbance.

SEABED CORING

JUMBO VIBROCORER

Carma coring has designed a Jumbo

VibroCorer to reach coarser

sediments It has barrel length of 6m

and a weight of 8200Kg.

A keynote of the design is the

self-recovery system. Once

penetration is complete, a

command from the deck returns

the iron barrel to its original

position. This greatly reduces

the possibility of bending the

barrels during extraction. With

this feature, a ship with DP is not

mandatory.

A patented tilting system allows

for the instrument to be

positioned horizontally when

close to the water surface

through the action of two

hydraulic cylinders. This

facilitates operations in rougher

seas since the centre of gravity

of the instrument, when

horizontal, is significantly lower

than the centre of gravity of the

classic vertical vibrocorer.

The Corer is equipped with 4

retractable stabilisers,

Jumbo VibroCorer

Jumbo

VibroCorer

placed

vertically

on the

seabed

Core Sample

independently hydraulically

operated and equipped with a

transducer, to always know the

instantaneous position of each

support foot with respect to the

structure. The features of the

stabilisers allow to sample

seabeds with 43deg slopes.

The vibrator is unidirectional with

hydraulic drive. Its force and

frequency are adjustable (0 – 54

KN and 0 – 2200 rpm/1° RPM,

respectively).

There is also a quick release plier

on the tube which enables quick

attachment/release of the core

barrel: in an extreme emergency

it is possible to free the machine

and abandon the barrel stuck in

the seabed. This possibility is not

likely, as the extraction

thrust exerted with the four

stabilisers reaches 200 KN in

total.

The JVC is moved with two

cables to a maximum depth of

250m: the dedicated winch has

a 20t load-bearing cable. The

second cable is a constant

tension winch and is used for

data and power transmission.

SEABED CORING

A subsea multi corer, is designed to

collect undisturbed sediment

samples from the seafloor. Its

primary purpose is to provide

researchers with intact cores that

preserve the delicate transition

between seawater and the

underlying sediment, a zone critical

for studying biogeochemical

processes, benthic organisms, and

environmental change, enabling

scientists to obtain reproducible

samples that maintain both

structural and chemical integrity

from deployment to analysis.

The device is typically constructed

as a heavy-duty frame capable of

carrying multiple transparent core

tubes, usually between six and

twelve, although some designs can

accommodate more. These tubes

are arranged symmetrically to

ensure even penetration into the

seabed.

The corer is lowered from a

research vessel on a winch cable,

descending through the water

column until it contacts the seafloor.

The weight of the frame allows the

tubes to sink vertically into the

sediment.

It has the ability to seal both the

bottom and top of each tube

immediately after penetration. This

prevents the loss of fine particles,

pore water, and fragile stratification

layers that are essential to accurate

scientific interpretation.

The result is a set of samples that

represent the seafloor often

including several centimetres of

overlying water for contextual

analysis.

A single deployment yields

multiple identical cores that can

be allocated to different lines of

investigation. One set of cores,

for example, may be sliced and

preserved for chemical assays

measuring nutrient

concentrations, heavy metal

accumulation, or organic carbon

content.

Another set can be examined for

benthic organisms such as

meiofauna or microbes, while

others may be reserved for

physical analyses such as grain

size distribution, porosity, or

sediment accumulation rates. By

generating parallel samples

under identical conditions, the

device reduces variability

between tests and supports

more robust cross-disciplinary

comparisons.

Multi corers are designed to

operate at extreme depths, in

some cases exceeding 6000m

Applications include

Environmental Impact

Assessments, Microplastics

distribution surveys, Pore water

chemistry, Geochemical analysis

Interstitial waters, Oil field

cuttings piles, Benthic layer

interactions and Biological

(eDNA) survey

MULTI- CORER

Multi-Corer Craig Smith, University of Hawaii

ROV PUSH CORERS

Push corers are compact,

manually operated sediment

sampling tools designed for

deployment via ROVs to collect

undisturbed sediment cores from

the seafloor. These are particularly

effective for obtaining high-

quality samples from specific

seabed locations, facilitating

biological, chemical and

geotechnical analyses.

“Push corers are essentially quite

simple devices, but there are

aspects that have evolved over

many years to make them

capable units.” said Terry Sloane,

MD, Planet Ocean.

“ They allow operation at great

depth, and with great precision,

making use of the host ROV or

manned submersible capabilities.

Our PC-range of corers have

been used to “full ocean depth”

as part of the world's first manned

expedition to the deepest point

in each of the five oceans.”

The core barrel is typically

fabricated from acrylic or

polycarbonate tubing to allow

visual inspection of the sample,

although stainless steel or

aluminium barrels are used when

higher structural strength is

required.

Standard barrel diameters range

from 30 to 60 mm, with wall

thickness selected to balance

rigidity against penetration

resistance.

The core tube is mounted onto a

stainless steel or corrosion-

resistant housing equipped with a

handle, compatible with ROV

manipulator arms. Using this, the

push corer is manually inserted

into the sediment

Barrel lengths rarely exceed

600mm due to the limited thrust

force an ROV manipulator can

exert without compromising

vehicle stability. Upon reaching

the desired depth, the corer is

withdrawn.

The top assembly incorporates a

venting system, commonly a one-

way valve or open port, which

permits water to escape during

penetration and prevents

hydraulic lock that would

otherwise resist insertion.

Upon withdrawal, a check valve or

rubber sealing bung engages to

retain the core and prevent

washout. The lower cutting edge

is beveled or reinforced with a

stainless-steel shoe to reduce wall

friction and improve penetration

efficiency.

Operational performance is

dictated by the manipulator’s

available thrust and grip strength,

which typically ranges between

100 and 300N for work-class ROV

manipulators.

In practice, penetration depth is

strongly dependent on sediment

shear strength: soft silts and clays

allow full barrel penetration, while

coarse sands or consolidated

sediments can limit recovery to

less than half the barrel length.

The ROV must maintain sufficient

station-keeping precision to

avoid lateral loads that would

bend the barrel or disturb the

sample.

From an engineering standpoint,

push corers represent a

compromise between structural

simplicity and functional

reliability. They cannot match the

depth or volume of hydraulically

driven or piston corers, but their

ease of integration with a wide

range of ROV platforms and their

ability to retrieve minimally

disturbed surface sediments

make them indispensable in

offshore engineering, subsea

environmental surveys, and

geotechnical reconnaissance.

Planet

Ocean’s EE

PC-1 and EE-

PC 2

sediment

coring

devices

A basket of Planet Ocean’s sediment

coring devices

SEABED CORING

ROV-DRIVEN CORING

ROV DEEP FRAME ROV CORERS

Norfolk-based Benthic Solutions

has unveiled its next-generation

Deep Frame ROV Corer,

engineered to deliver superior

subsea sampling performance.

Prior to this innovation it was not

possible to acquire deep core

samples from cuttings piles

beneath existing infrastructure,

now making it possible to cost

effectively obtain more accurate

lithological characterisation of

cuttings piles for

decommissioning planning

purposes

Capable of penetrating up to

2.2m into the seabed—nearly

double the 1.2m capability of

the original 2012 design—the

system represents a

significant leap forward in

offshore coring technology.

The Deep Frame ROV

Corer is highly versatile,

deployable either by

subsea crane or mounted

to the front of a work-

class ROV (wROV) using

a five- or seven-function

manipulator.

Each sample is captured

in a semi-translucent PVC

liner (89mm OD), providing

clear visibility of substrates

and lithological layers for

accurate sub-sampling and

analysis. With consumable core

barrels, samples can be securely

capped, stored, or sectioned into

fixed lengths, ensuring safe

transport and streamlined

laboratory processing.

“Since launching the original

system, we’ve introduced several

key innovations,” explained

Managing Director Simon

Redford. “These include an

internal piston, a robust chain-

drive arrangement, and the

integration of two independent

2050-DSS

COMBINED

SIDE SCAN SONAR

& SUB-BOTTOM

PROFILER

• Versatile: Tri-Frequency

Side Scan to cover a

range of applications

• Capable: Towfish based

CHIRP Sub-bottom profiler to

deliver higher resolution data

• Loaded: Built-in pressure

(depth), heave, pitch and

roll sensors

• Flexible: Support for

3rd party sensors

NOW 3000m RATED

SEABED CORING

Deep Frame ROV Corer

being crane-deployed

Image: Benthic Solutions

Box Corer

ROV Box Corer

samplers on a single lightweight

frame. The design consistently

delivers high-quality 89mm

diameter cores.”

This dual-sampler setup enables

multiple site investigations or

replicated samples within a

single dive—whether by

acquiring duplicate cores from

one location or sampling two

distinct sites. Once deployed,

the cores themselves act as

suction anchors, providing

exceptional stability throughout

operations.

ROV BOX CORER

The ROV box corer is essentially

a smaller and more portable

version of the traditional box

corer.

Benthic Solutions unit has a

reduced surface area (0.1m})

which allows for relatively large

sample sizes to be recovered in

deep water utilising a ROV. The

instrument is triggered by the

ROV lifting the unit. The depth

of penetration (maximum 45cm)

can be controlled via the ROV to

prevent over-penetration in

softer sediments.

The recovered sample is

completely enclosed after

sampling, reducing the loss of

finer materials during recovery.

Stainless steel doors, remain

loose during the deployment to

reduce any "bow-wave effect"

during sampling and remain

tightly closed, sealing the

sampled water from that of the

water column on recovery. This

makes the device ideal for

structured sediments in sites

difficult to reach using

conventional means (such as

cuttings piles and sites very close

to existing infrastructure).

The box corer can be

deployed to the seabed via a

dedicated basket, or

can be carried

directly by the

vehicle. Multiple

corers can be used if

replicate samples are

required. On recovery to

the vessel/platform, the

sample can be processed

directly through the

access doors on the top

of the unit.

Constructing permanent

structures on the ocean floor can

be extremely challenging, and a

change in plans can equate to

millions of dollars in modifications

and delays.

So how can offshore energy

developers decrease risk to their

budget and timelines when there

are so many unknowns at the

beginning of a project?

Kraken Robotics’ Acoustic Corer

(AC) is a cutting-edge subsea

survey system that bridges the

gap between geophysical and

geotechnical investigation

methods by delivering high-

resolution, 3D acoustic imagery of

the sub-seabed.

By providing insight on the

geology of the sub-seabed, the

AC can significantly de-risk

offshore development plans,

saving developers from needing to alter designs due to

geological hazards later in the installation process.

THE ACOUSTIC CORER TECHNOLOGY

The system comprises a suite of acoustic survey sensors

which build up a high-resolution 3D acoustic volume below

the seabed, within which, geohazards can be identified

and geological units interpreted and correlated to

geotechnical results.

These sensors include a high-frequency chirp operating at

4.5 kHz to 12.5 kHz, which enables the Acoustic Corer to

identify boulders as small as 0.2m in the sub seabed, a low-

frequency chirp operating at 1.5 kHz to 6 kHz, enabling

penetration greater than 50m below the seabed, and a

parametric transceiver, operating at multiple frequencies,

which supports geological mapping.

By combining multiple sensors, the Acoustic Core

produces a 14m diameter data set which penetrates the

seabed. Depending on lithologies, penetration achieved is

regularly down to >50m below the seabed.

By measuring backscatter energy within the sub seabed,

the internal patented processing system images the

exterior of isolated anomalies such as boulders, producing

centimetre accurate dimensions and XYZ

location, whilst the parametric sensor

provided lithological context,

delineating boulder-

strewn

layers

and

providing

geotechnical

context. The system has been used across numerous

industries for various applications:

DECOMMISSIONING

The Acoustic Corer can be used to locate

deeply buried assets to confirm exact locations

Kraken acoustic corer

INSTALLATIONS

DE-RISKING SUBSEA

WITH KRAKEN ROBOTICSʼ ACOUSTIC CORER

and integrity to support

decommissioning plans. It has

also been used to identify

hydrocarbon leaks from buried

conductors and flowlines.

SITE INVESTIGATIONS

The Acoustic Corer enables

identification of buried boulders

>0.2m in diameter to depths in

excess of 50m below seabed.

The data has multiple functions

including the ability to support

foundation design as well as

foundation installation strategy

and methodology.

The main application is the

support to foundation installation

campaigns to provide boulder

locations, enabling micro siting of

foundations or the risk to be

appropriately managed and

mitigated through engineering

and installation methodologies,

protecting schedules and costs

from unforeseen soil conditions.

ABANDONED WELL

LOCATION AND RE-ENTRY

The Acoustic Corer can

accurately locate XYZ positions

of abandoned wells with

centimetre accuracy, assessing

conditional integrity and

presence of sub-surface debris

and hazards.

Once acquired, preliminary

results of the well position are

produced offshore within 24

hours of data acquisition,

enabling infield decisions to be

made and initial risks or survey

objectives reviewed, with final

reports issued after

demobilisation.

Survey methodologies can be

tailored to the survey objective,

from single scans at individual

locations, triple overlapping

cores which are merged into a

single 3D volume to provide

greater coverage and enable

micro siting, or, for large areas,

numerous overlapping cores

can be acquired and merged

into a large-scale 3D volume to

enable regional ground models

and wider geological context

to be achieved.

PROJECT CASE STUDY –

GENNAKER OFFSHORE WIND

FARM BOULDER SURVEY

With its geographic location

within the Baltic Sea, the

Gennaker Offshore Sub Station

(OSS) is in an area of complex

seabed and sub-seabed

conditions.

The purpose of this survey was

to identify the presence of sub-

seabed boulders with

diameters of 0.2m or greater.

Previous towed 3D seismic

surveys had failed to deliver

the required resolution,

therefore the client requested

the use of the Acoustic Corer

which, by combining High-

frequency chirp (HF), Low

frequency chirp (LF) and

Innomar chirp sources, can

achieve market-leading

resolution, penetration and

accuracy.

The aim of the project was to

mitigate the risk of buried

boulders to the safe and

efficient installation of the two

Interpretation of Acoustic Corer data

SEABED CORING

OSS, each with four caisson suction bucket

foundations. The survey was required to map

0.2m diameter cobbles/boulders and

penetrate to 15m below the seabed.

Each leg location consisted of a triple acoustic

core; three 14 m diameter acoustic cores were

collected and merged in a triangular pattern

to form a single interpretable acoustic

volume. Each acoustic core was laterally and

vertically aligned to ensure a continuous

response with no offsets between each

acoustic core and the overlapping scans.

The seabed and geological conditions were

variable throughout the survey area, with the

presence of seabed boulders and coarse

sands.

Despite the unfavourable conditions, the AC

signal penetration was sufficient to resolve

cobbles and boulders through the sediments,

with a total of 1057 acoustic anomalies

suggestive of cobbles/boulders interpreted

across 24 scan locations.

Following the delivery of results, the client was

able to ensure the design of the caisson

suction buckets took into account the onsite

geological conditions and that each pile

would reach the required depth of

penetration.

The foundations’ locations were also

modified, rotating the OSS within the

footprint of the 3D data set to remove the risk

of encountering cobbles/boulders during

installation, enabling accurate installation

forecasts and reducing the commercial risk to

the project.

Having collected thousands of acoustic cores

across North America, throughout NW Europe

and the Baltics and Asia, Kraken Robotics’

Acoustic Corer reduces risk to offshore

developments and increases sub-seabed

clarity.

Triple acoustic core results compared to another

3D acoustic system’s results. The hashed red area is

from the other 3D acoustic system and the dots are

the AC results.

Plan view depth slice within a triple acoustic

core showing anomalies suggestive of boulders.

SWORD

Aratellus’ Subsea Wireline

Operated Remote Drill (SWORD)

system has recently been

commissioned in Port of Blyth

after a number of upgrades and

capability enhancements. The

system was originally equipped

with a sonic based drilling system,

producing very high-quality

samples in specific soil conditions,

it now being upgraded to a new

powerful hydraulic rotary system.

“We began to realise that in

harder lithologies, the sonic

based drilling becomes more

challenging, particularly when the

drilling is carried out remotely,”

said Jamie Linton, Project

Director.

“In the last few months, therefore,

we have been installing

modifications to help optimise the

drill in a much wider range of

geological materials – in many

ways making the SWORD a new

system. We have just completed a

commissioning and testing

campaign in Port of Blyth,

particularly with reference to a

land rig that we brought in and

had drill the same locations.

The ability to study the

comparative data has given us a

great confidence in SWORD’s

capabilities.”

“Previously SWORD was based on

a sonic drill system. We made the

decision to install a rotary

Eurodrill 400 motor drill head –

making the system the most

powerful drill head fitted to a

subsea drill. We’ve also upgraded

the surface control system with

The SWORD is lowered by a umbilical

SEABED CORING

greater feedback to the operator.”

Subsea drills such as SWORD have

a unique benefit over conventional

vessel-based drilling systems by

not being subject to the vessel

motions once in the water, able to

remain operable in much greater

sea states, greatly improving

productivity, sample quality and

reducing site investigation costs.

HOW IT WORKS

The SWORD is lowered by a

mainlift umbilical, much the same

as an ROV or Trencher, landing out

on the seabed. It has three legs,

each controlled independently to

ensure the system is level and

stable, even when positioned on

an undulating seabed.

The drill string and all associated

sample tooling are securely stored

within the SWORD carousel

system. The drill string is

connected to the subsea drill head

via an automated sequence, fully

controlled from the surface.

Drilling samples are stored within

the subsea carousel and retrieved

using the same automated tool-

handling arrangement.

“In many drilling systems, the

sample enters the core barrel that

rotates with the drilling action,”

said Linton. “This rotational

spinning can greatly disturb the

sample.

In SWORD, however, using the

Geobore-S system, the coring bit

still turns to make the hole, but the

sample enters a plastic liner within

a secondary barrel within the drill

string, it is latched at the top. The

sample stays securely in position

within the liner simply through

friction, isolated from the

rotation of the outer drill pipe.”

Once an individual 3m long core

is taken, the sample and barrel

are retrieved by the wireline

system upwards and are then

stowed into an empty slot in the

storage carousel. The carousel

then revolves to present a new

core barrel into to the firing line

of the drill. The new empty

barrel with plastic liner is

lowered by the wireline down

the string and into the latch

allowing drilling to recommence.

SWORD can drill multiple holes

in different locations prior to

being recovered.

Once all the slots are filled, the

SWORD system is retrieved back

to the vessel so that the

geotechnical engineers can start

to analyse and log the samples,

there’s an automated handling

system on the deck as part of the

spread.

The SWORD control systems

incorporates a tracking system

that allows a greater control of

chain of custody by digitising

where each sample has been

taken and stored in the carousel.

The total depth of the hole and

sampling depends on the data

required by the geotechnical

engineers and the purpose of

the site investigation; SWORD

has the capability to drill down

to 140m in water depths of up to

3000msw. Typically, a cable route

needs a lesser depth sample,

SEABED CORING

but larger bodies such as the installation of a wind turbine

foundation would require a much greater depth investigation.

SAMPLING

In addition to the Geobore-S core samples there is the capability to

run Mazier and Shelby push sampling along with downhole Cone

Penetrometer Testing (CPT).

A Shelby Tube is a thin wall open tube sampler designed for taking

undisturbed samples in soft to firm cohesive soils. These tubes are

pushed down into the ground and importantly, not rotated which

may disturb the sample. Once it is pushed down, a non-return valve

is closed at the top of the sample tube to retain the sample.

Another type of sample is the Mazier. This can also be used with

non-rotational pushing. The Mazier sampler is designed to obtain

samples in soil conditions that are too hard for Shelby tube

sampling, but not yet hard enough for conventional coring.

This can be particularly useful in sample runs that have strata

changes that would otherwise make it difficult to maintain sample

quality using standardised tooling.

In addition, SWORD can be used for downhole CPT where it is used