579
1 BALTICSEA
Baltic Sea in a mediterranean sea of an Atlantic
Ocean,situatedinitsnorth‐easternpart.Enclosedby
mainland Europe from south and east and by
Scandinavian Peninsula from north and west, it is
onlyconnectedtotheoceanbynarrowDanishStraits.
Itisalsoveryshallowwithmediumdepthofonly55
metresandma
ximumoflessthan460metres.Itcan
be covered by ice in an extent of up to 45% of its
surfacearea,especiallyinthenorthernpart:Gulfsof
Bothnia and Finland but southern part can also be
affected by ice accumulation during severe winters.
Geologyofthesurroundingareawasformedmainly
duringglacialepisodes(globalcoolingandwarming)
and was furt
her enhanced by effluents from the
numerousriversflowingintoit.Thatcreatedaseabed
coveredbyvariouskindsofsediments,rangingfrom
loam (east of Bornholm and in Gul
f of Gdańsk)
through fine‐grained sand (Bay of Pomerania) and
coarse sands (along the shore) to gravel and stones
(Słupsk Bank)‐geological conditions are very
complexandcanvarysignificantlyeveninrelatively
small areas. Each of sea bottom kinds has some
characteristicfeaturesdescribingitsabilitytosupport
nearshoreandoffshorestructures (Kaszub
owski,L.J.
&Coufal,R.2008).TheBalticSeaischaracterizedby
little variationin waterlevel, withalmost negligible
tiderange.Sea currentsareweakwithusualsettingof
¼ knot which however can be increased even to 2
knotsbygaleforcewinds.Thosecondit
ionscombined
makeBalticSearesembleabig,navigablelakerather
than a sea. Main natural resources include: oil and
gas,windenergy,sandandmarineorganisms.
The specificnatural conditions of BalticSea have
many practical implications. The most important of
them is a low salinity of the water, caused by it
s
limitedexchangewithanocean,significantinflowof
freshwaterfromtheriversandseabedtopographyin
Danish Straits. Here the salty oceanic water, being
heavier than the fresh one, encounters banks and
shallow areas and only in certain conditions a great
mass of ocean water finds its way to theBalt
ic Sea.
SuchphenomenonusuallyoccursinlateAutumnand
Winter,themostrecentoneinDecember2014,when
Specificity of Geotechnical Measurements and Practice
of Polish Offshore Operations
B.Łączyński&K.Wróbel
GdyniaMaritimeUniversity,Poland
ABSTRACT:AsoffshoremarketinEuropegrowsfasterandfaster,newseaareasarebeingmanagedandnew
ideason how to use theseapotentialarebeing developed. In North Sea,whereoffshore industry conducts
intensiveexpansionsincelate1960s,numerouswindfarms,oilandgaspla
tformsandpipelineshavebeenput
intooperationfollowingextensiveresearch,includinggeotechnicalmeasurement.Recently,agreatnumberof
similarprojectsisunderdevelopmentinBalticSea,interaliainPolishEEZ,naturalconditionsofwhichvary
fromtheNorthSeasignificantly.Inthispaper,thosedifferencesaredescribedtogetherwithsomesolutionsto
problemstherebyarising.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 9
Number 4
December 2015
DOI:10.12716/1001.09.04.16
580
as much as 198 cubic kilometres of saline water
reachedBalticSea,makingitthethirdlargestinflow
ever observed. Ice accretion also contributes to
changes in salinity (Mohrholz, V. et alia. 2015).
Furthermore,astrongstratificationofBalticSeawater
can be observed, with upper layer containing
significantly less
salt than the lower one with
halocline separating them. Shallowness and a
relativelylowvolumeofwatermakesitvulnerableto
temperature changes – it resembles a lake in this
matter. Sea water temperature varies from 0°C in
Winterupto18°CinSummer.
Years of progress in surrounding countries’
agriculturewithoutregardtoenvironmentprotection,
especially in former socialist countries led to
enormous accumulation of fertilizers originally used
toboostcropsashore.Thosenowledtorapidgrowth
of marine organisms‐especially algae‐lack of
oxygen in lower layers of the sea and eventually to
vast portions of the seabed
turning into ‘deserts’
insteadofareassupportingmarinelife.
To complement an analysis of conditions
influencing the geotechnical measurements in Baltic
Sea,some attentionmustbepaidtohuman activity,
especiallyinthepast.Firstofall,Baltichasbeenused
for trade purposes for centuries with some authors
dating
such activity back to the times of Roman
Empire and further to the past. Some underwater
investigations led to discovery of settlements dating
back to 7000 BC (Fischer, A. 1995), not to mention
morerecentlysunkenwrecksof‘Vasa’and‘Wilhelm
Gustloff’,allofthoseconstitutingsignificanthistorical
and cultural value
and can limit human activity in
certainareas.Suchcanalsobecausedbyoldchemical
weapon, only to mention sulphur mustard, sunk in
theBalticSeaafterWorldWarIIbyvariousnations.
Its quantity is estimated to be around 32 thousand
tonnes (Missaien, T. et alia. 2010) and
it causes
significant risk to marine and human life, especially
when tampered with. Areas in which it can be
encountered have been identified and shall be
avoided by any vessels conducting seabed‐related
activities,suchasanchoring,trawlingorconstruction.
The Baltic Sea is administratively divided into
sectorsoverwhicheach
coastalstatehasajurisdiction
as per UNCLOS – territorial water and exclusive
economiczonewhicheverthecasemightbe.Manyof
coastal states introduced some elements of spatial
planning, covering their areas of responsibility and
describing what activities might be performed in
those. Some had been excluded from the
authorization to perform drilling or any similar
activitiesduetoenvironmental,historicalormilitary
reasons.
2 GEOTECHNICS
Geotechnical engineering, also referred to as
engineering geology, is a scientific discipline of
applying geological knowledge to engineering or
constructionproblems.Practically,itcanbedescribed
as an art of calculating mutual interactions between
soilandman‐madestructures.
Future offshore construction site investigation
process can be divided into three parts: desk study,
geophysicalsurveysandgeotechnicalsurveys.Infirst
stage,informationaboutplanneddevelopmentareais
gathered from available sources, i.e. environmental
reportsofscientificliteratureandanalysed.Itisthen
decidedwhat
rangeofgeophysicalresearchshall be
performed in situ. This includes: seismic survey,
precisebathymetry,sub‐bottomacousticprofilingand
use of underwater vehicles to investigate areas of
particular consideration. Results of those are
complementedby geotechnical surveys consistingof
seabedsampling,drillingandlaboratorysoiltesting.
Inoffshoregeotechnical
engineering,morefactors
apply and it is generally more difficult to perform
surveysthanashore.Reasonsforthisare:
possible existence of ocean currents and waves,
generallystrongerwindoverseaareathanonthe
land–whichcombinedcreatesignificantloadson
thestructures;
other natural conditions not
present in onshore
environment,e.g.presenceofhydrates;
planned structures reach hundreds of meters in
height which requires their foundations to be
particularlywell‐designedandinstalled;
hydroacousticsbeingvirtuallytheonlymethodof
remote sensing in sometimes hundreds‐of‐meters
deepwater;
necessity of employing dedicated
research ships
with highly sophisticated equipment and well‐
paid crews (including divers) which increases
costsofsuchoperation.
3 GEOTECHNICALMEASUREMENTSINBALTIC
SEA‐CONDITIONS
As a consequence of above described conditions
specificforBalticSea,therearesignificantdifferences
betweentheway thegeotechnical measurementsare
beingperformedinthe
openseasandintheBaltic.
Firstly, as a Baltic Sea bathymetry was surveyed
extensively by coastal states, major hazards for
surface navigation and other activities have been
identifiedandarequitewell‐known.However,arisk
ofencountering ofIIWorldWarseaminesorwrecks
stillexistsand
mustbetakenintoaccount.Awrecked
aircraft carrier ‘Graf Zeppelin’ was found, for
instance,accidentallyduringroutinesurveyofB3oil
fieldinPolishEEZ.
When carrying on a hydroacoustic survey, it is
characteristicforaBalticSeathatthemostimportant
factorinsuchactivities,whichissoundspeed,
varies
significantly depending on changes in sea water’s
salinity and temperature. Those in turn, highly
depend on air temperature (varying seasonally), ice
coverage, volume of water inflows from rivers and
North Sea. Furthermore, stratification of water into
twolayers:upper(lesssaline)andlower(moresaline)
creates additional difficulties. To
cope with such,
sound velocity profile (SVP) in water must be
monitoredandpropercorrectionsapplied.Moreover,
asmostofhydroacousticdevices,i.e.echosounderor
sonars are designed to be used in seas of
approximately 35 PSU salinity, lower salinity causes
581
theirrangetodecrease(Grelowska,G.&Kozaczka,E.
2005).
Asmultibeamechosounders(MBES)andside‐scan
sonars(SSS)are widelyconsideredas veryuseful in
imaging of the seabed itself (Gerwick, B.C.Jr. 2000),
there are two main methods of its structure remote
investigation: seismoacoustics and non‐linear
acoustics.First
oneisbasedoncreatingstrongpulse
of acoustic wave which penetrates the seabed and –
reflected by interphase boundary between different
layersofsediments(orothercharacteristicobjects,i.e.
buriedshipwrecks)isthenreceivedbyhydrophones,
placed on state‐of‐the‐art devices towed abaft of
seismic vessels called
‘streamers’ as can be seen in
Figure 1. This method enables large areas to be
surveyed in a time, cost of such operation being
enormousdueto ahighcharterratesfor specialized
vessels. It is therefore only practicable in large
offshoreprojects.
Figure1. Principle of seismoacoustic survey.
http://captainsvoyage‐forum.com/.Retrieved15‐06‐2015.
Aparametricacousticsmethodenablessmallboats
to survey a seabed in relatively small areas using a
single but modified echosounder. Here, an effect of
interaction between two high frequency acoustic
wavesofasmalldifferentialfrequencybetweenthem
allows for creation of a secondary hydroacoustic
wave that enables good seabed
penetration and
vertical resolution simultaneously. Detailed
description of this method and results of survey
utilising it can be found in (Grelowska, G. &
Kozaczka, E. 2008). A major disadvantages of this
method is that a sound velocity in a kinds of
sedimentsbeing likelytoencounter during a survey
mustbe known a priori,and as one cannever know
whatkindofseabedliesbelowanupper‐mostlayer–
parametricsoundingcanonlybeusedinconjunction
with old‐fashioned core sampling. Knowledge
possessed from core sampling is then used for
sediments’ layers acoustic impedance estimation.
Poor
efficiency of secondary wave is also an issue
(Lurton, X. 2010). All those factors combined make
parametric sounding useful in surveying relatively
small areas with shallow water, geological structure
of which is roughly known, like Baltic Sea for
instance.
Afterageophysicalsurveyiscompleted,designers
of a future oil field
or offshore wind farm possess
some knowledge regarding its ability to support
structures. However, coastal states require more
detailed investigation to be performed in the exact
locations of i.e. wind turbines. For example, Polish
Ministry of the Environment’s regulations rule that
for each and every wind turbine,a core penetration
test(CPT)mustbecarriedout(orundereachofjacket
structure legs). Furthermore, core sample drilling
must be performed in each of future wind farm’s
cornersand inits central partandsamples acquired
arethentestedinthelaboratoryagainstitsmoisture
content,drydensity,particlespecificgravity,particle
size distribution, Atteberg limits and carbonate
contentetc., sometimes also particle mineralogy and
geologicalclassification(X‐raytesting)(Randolph,M.
et alia. 2005). Those requirements can be more
stringent whenever deemed necessary. Apart from
obvious differences in the way a wind farm
construction project is developed in onshore and
offshore
environments, a requirements concerning
siteinvestigationaremorestrictinthelattercasedue
to an unstable nature of seabed sediments being a
highly unpredictable environment. Hydration of
seafloor creates major concern and sometimes can
even cause difficulties in determining where exactly
liestheboundarybetweenwaterandseabed.
4 DAY
‐TODAYOPERATIONSINPOLISHEEZ
Lotos Petrobaltic, member of partly state‐owned
Lotos Group, is the only entrepreneurship in Polish
EEZhavinglicensesforoilandgasexploration(Fig.
2) and one of the most active ones in terms of
geological and geotechnical surveys. It operates two
drilling platforms, same
number of exploration rigs,
two AHTSs and guard vessels, oil tanker and a
research vessel ‘St. Barbara’ (Fig. 3). It is also an
ownerofathermalpowerplantnearWładysławowo
ina northernmostpartofPoland.Thecompanyitself
was created as a joint venture by Soviet Union,
German Democratic Republic and Polish People’s
Republic in late 1960s. Most of field development
projects have been ever since conducted by its
employees without significant support from oil
majorswhichledtotheformationofhighlyqualified
team of specialists. Geotechnical measurements, the
preliminary stages of field development were
conducted
from the deck of ‘St. Barbara’ (2324 GT,
app.80meterslong,inoperationsince1977).Sheisor
may be equipped (according to actual operational
needs)with:
Drillingrig;
Down‐holepenetrometer;
Vibrocorer;
Moonpool;
Cesiummagnetometer;
Multibeamechosounder;
Side‐scansonar;
Seismoacoustics
equipment;
USBLunderwaternavigationsystem;
RemotelyOperatedVehicles(ROVs).
Most notable projects conducted by ‘St. Barbara’
are: survey of future gas pipeline track from B3 oil
field to Władysławowo, bathymetrical and
magnetometer surveys in the oil fields, CPTs of
plannedwindfarms,coresamplinginfuture
drilling
sitesetc.Shealsotookapartinextractionoperationof
aDouglasA‐20aircraftwreckfromtheseabed.
582
Figure2. Hydrocarbon production licenses of Lotos
Petrobaltic.http://www.lotos.pl/Retrieved05‐06‐2015.
Figure3.Researchvessel‘St.Barbara’.http://www.lotos.pl/
Retrieved05‐06‐2015.
Itisacommonpracticeforthisvesseltoconducta
complex geotechnical survey of a particular areas,
ranging from initial bathymetric soundings using
multibeamechosounder,thenmoredetailedscanning
by a towed side‐scan sonar. Those two surveys can
onlyprovide information regarding seabed’s surface
which makes additional tests necessary.
Seismoacoustic methods can be applied but their
great disadvantage is that even if a big anomaly is
found – it is difficult to determine whether it is a
naturalfeatureorofahumanorigin(thelatterbeing
generally more dangerous as it could be explosive,
chemical weapon etc.). That
is why magnetometer
scanning is performed and in case of any magnetic
anomaliesbeing found – ROV investigation follows,
which enables for some detailed view. ROVs are
equipped with digital cameras and short‐range
sonars.Whenatthisstagethesiteisconsideredclear
and deemed safe for construction of offshore
structures, a final analysis is carried out which
includesCPTtestsandcoresampledrilling.Samples
obtainedthiswayorbyagrabcanbeanalysedinan
on‐board laboratory. In an oil rig’s case, CPT is
conducted under each of future structure’s legs and
drillingtoapproximately30
mintotheseafloortakes
place in the exact position where future borehole is
planned.Forapipeline,CPTsaredonealongitsroute
ina distanceof200‐300metersonefromanotherand
adrillingfor one in three CPTs’ positions. All those
surveyscombinedgiveagoodinformation
regarding
bathymetry,unexpectedobjectslyingontheseafloor
and its geological structure. Proper design, quality
controlduringmanufactureprocessandthoroughsite
investigationcreatesconditionforasafeoperationof
astructureineachstageofitslife,takingintoaccount
factors such as: settling, dynamic loads, soil
liquefaction and
erosion and reducing geotechnical
hazard.
Figure4.Typicaldetectionrangeofcesiummagnetometer.
M‐882Magnetometerspecification.Geometrics,Inc.
One of the biggest challenges in conducting the
abovetestsisaprecisenavigationsince‘St.Barbara’is
notequippedwithadynamicpositioningsystem.Itis
a particularly difficult task during magnetometer
surveys as an instrument itself is towed behind the
vessel’ssternandmustbelocatedwithin2.5m
range
fromapre‐plannedprofileitshouldfollowinorderto
detecttheanomalies.Furthermore,thesensormustbe
positioned approximately 3 to 7 meters above the
seabed(4metersasanoptimum)byoperatingtowing
winch.Ifoneconsidersa200oreven300meterslong
umbilicalconnecting
thedevicetotheship,influence
ofwind,wavesandcurrentandanavigator’sability
to control the vessel only by using rudder and
propellers, it is truly a masterpiece of navigation.
Vessel’s position and course are provided by GPS
with differential corrections received from DGPS
reference station in Rozewie, Poland.
Furthermore,
position of a magnetometer or side‐scan sonar in
relationto the ship is measured by Ultra Short Base
Line(USBL)hydroacousticnavigationsystemandcan
be imposed on a map showing profiles. Entire
operationiscontrolledbyaQinsysoftwaredeveloped
byQPSBV.Evenifalldata
gatheredbyechosounder,
DGPS,USBL,towlinelengthsensoretc.aremutually
consistent(which not always mustbethe case), it is
stillanissuetodeterminewhetherananomalyfound
indicates existence of a small object lying on the
seafloororabiggeroneburiedinit.Typicaldetection
range of
cesium magnetometer is presented in a
Figure4.
583
Figure5. Layout of r/v “Imor’. http://www.im.gda.pl/.
Retrieved10‐06‐2015.
Another important branch of geotechnical
measurements in Polish EEZ refers to the nearshore
areas: ports, river estuaries, shallow water for
instance. Here, most of works is connected to ports
development projects like construction of a new oil
and container terminals in Gdańsk, gas terminal in
Świnoujście, nuclear power
plant in Choczewo and
others. Surveys are conducted by numerous motor
boats operated by private companies and by r/v
‘Imor’ (Fig. 5), a catamaran owned by Maritime
Institute in Gdańsk, which is equipped with: MBES,
SSS, USBL, ROV, vibrocorer, magnetometer, boomer
andDPclassI.Duetorelativelysmalldraught
of2.3
meters,sheiscapableofconductingcomplexresearch
eveninquiteshallowareasandmaybesupportedby
othervesselsoperatedbytheInstituteofevengreater
operationalabilitiesinanearshoresector.
5 CURRENTOFFSHOREACTIVITYINPOLISH
EEZ
AsofJune2015,majoractivitiestakingplace
inPolish
Exclusive Economic Zone are: hydrocarbon
production and distribution (by shuttle tanker and
gas pipeline), seabed resources exploitation
(aggregates,i.e.sand),constructionofobjectsaiming
incoastprotection,constructionofnewcontainerand
oil product terminalsand investigations on the sites
of projects at different stages of development, of
which
the most notable are: wind farms, Mierzeja
Wiślanacrosscut,CNGterminalinBayofPuck,new
gaspipelinetoconnectB8oilfieldwithpowerplantin
Władysławowo.
Thecompanybeingthemostactiveinthissectoris
Lotos Petrobaltic, member of Grupa Lotos. With
annual production of
approximately 1.2 million boe
onlyfromitslicenseinPolishEEZ(B3field,Fig.6),it
is one of the biggest hydrocarbon production
companies in the country, supplying oil and gas to
variouscustomers,includingarefineryinGdańsk.In
afewmonthstocome,itisplanningtocommence
a
productionin B8fieldwith preparations forstarting
upatightgasproductioninfurtherareas.
Figure 6. Layout of B3 oilfield infrastructure.
http://www.lotos.pl/Retrieved05‐06‐2015.
Abranchofoffshoreeconomythatmanyhopeto
developinanearfutureiswindfarming,particularly
when taking European Union environmental policy
into consideration. Special planning process allowed
maritime administration to identify few areas in
which such projects might be developed by private
companiesandanumberoflicenses
hasbeenissued,
however there are still administrative, technical and
fundraisingproblemstobesolved.Firstelectricityis
expected to be produced in south‐eastern Baltic in
nextdecade.
6 CONCLUSIONS
However underdeveloped Polish offshore sector can
be regarded, especially comparing it to highly
innovative and profitable activities in not
so distant
North Sea, it is clear that capabilities of companies
engaged in offshore investigation business exceed
operationalneeds of theclients.The obstacles to the
developmentofPolishoffshoresectorarenotthelack
ofproperequipment or personnel being not enough
qualified, but the administrative, legislative and
sometimes lack
of assets among the enterprises
interested in nearshore and offshore activities,
includingoiland tightgasexploration, windenergy
etc. Research, investigation and measurements of
virtually any kind can be carried out by numerous
localcompanies,eveninconditionsspecificforBaltic
Sea,providedtheweatherpermits.
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