Journal Review APPLICATION HYDROGRAPHIC SURVEYS NATURAL
RESOURCES MANAGEMENT IN OIL AND GAS (OFFSHORE)A. INTRODUCTIONBefore
discussing more about the contents of the journal will first be
explained what is meant by hydrographic and oil
exploration.Hydrography is the science of making measurements,
menguraian, and develop on:a) The properties and configuration of
the seabed produced by bathimetrik surveys, geology and
geophysics;b) the geographical relationship (between the sea, the
waters) generated by the nearest land to
thepositioningactivities;c) The nature and dynamics of ocean water
generated by measurements / observations of tides, ocean currents,
waves and physical properties of sea water.Hydrographic science is
something that is very important to know in a variety of human
activities that occur on the surface and below the surface or the
sea or on the seabed.While oil exploration is the act or traveling
with the intention of finding sources of new oil reserves through a
long study involving several fields of study of earth and inexact
science.Oil exploration initially only be done only land area, but
with decreasing oil reserves and increased demand for fuel oil, the
oil and gas exploration was also carried out at the ocean.B. ROLE
hydrographic surveyIn the journal explained that the role of
hydrographic surveys in oil exploration are as follows.1.
PositioningPositioning at sea is a very crucial thing in all survey
activities at sea.Of course before doing the survey, we have to
know the position and direction of the ship moving so while doing
the survey, the survey vessel moves on a predetermined path.The
instrument is used in the positioning system DGPS, which is used
for positioning inreal timedifferential for moving objects (ship
surveys).To realize thereal-timedemands, it will send the reference
stationpseudorangecorrections to the survey ship navigator.2.
Bathymetry SurveyBathymetric survey was intended to obtain depth
data and configuration / seabed topography, including the location
and extent of objects that may be dangerous.The tools used in this
survey isMultibeam Echosounder.The working principle of this
instrument together witha single beamemittedbeambut the number is
more than one beam.Patterns radiance widened and transverse to the
hull.Each beam will get one point if the depth to the depth points
are connected to form a profile of the seabed.If the ship moves
forward multibeam sweep results produced an area that describes the
surface of the sea floor (Moustier, 1998).The bathymetric data will
also be useful to analyze the possible obstacles and estimate the
cost of infrastructure development rigs and subsea pipelines.3.
Observations PasutTidal observations carried out to obtain the
depth of the bathymetry corrections.Observations can use
apressure-typetidaltide gaugesplaced at a certain depth, so that
later the device will record the pressure difference, which will
provide data on changes in sea level.The tide gauge measurements
performed during the bathymetric survey.4. Flow MeasurementCurrent
measurement is done to obtain the data speed and flow patterns.This
data is needed for planning purposes the power infrastructure to be
built.Current measurement is done by usingDoppler Current Profiler
Acoutic(ADCP).The principle works, the device will emit an acoustic
wave with a certain frequency.Then the acoustic measuring
instrument measuring the frequency of the reflected waves are
reflected by materials (which moves with the same speed as the
velocity of the water).Because of the relative motion of the
reflecting wave acoustic flow measuring devices, the received wave
will experience the Doppler effect or change their frequency.This
frequency will be proportional to the velocity difference between
acoustic flow measuring instrument with the measured current
layer.If the current is moving away from the acoustic flow
measuring devices, the frequency of which will be captured will be
smaller and vice versa.In this there are 3 tools ADCP transducer,
which first experienced the movement flows east-west direction, the
second movement of currents observed north-south, and the third
observing the movement of the top-down flow.Of these vectors can be
determined direction of the current of each column were observed.5.
Measurement of physical properties of sea waterMeasurement of
physical properties of sea water is done using a CTD.CTD is an
instrument to measure water characteristics such as temperature,
salinity, pressure, depth and density.In general, the CTD system
consists of a data input unit / input, processing systems, and
output.The unit consists of a sensor data input CTD,rosette,sample
bottles and cable connections, penggolahan using existing software
such as the operating system ODV(Ocean Data View)and Microsoft
Excel and outputs a graph of the data station.(Hertikawati 2010).In
principle, the measurement techniques on the CTD is to direct the
signal and get the signal from a sensor that detects the amount,
then get the data fromthe multiplexmethod and coding(decode),then
break down the data by the method of the encoder to the transfer to
the serial data stream to be sent to the control unit via a cable
to a computer that is already installed.This measurement is done to
provide a correction for the velocity of acoustic waves in the
water columns specified.C. METHODS IN hydrographic surveys
PETROLEUM EXPLORATIONTo support eksplorasidan exploitation of oil
and gas resources at sea, can be used underwater acoustic
technology(underwater acoustics)that the hydrographic known as
Hydro-acoustic because of its use in the water.Hydro-acoustic
technology is the use of sound waves in the world of navigation
called Sonar orEchosounderand the like.1. Measurements
usingechosounderEchosounder is a tool to measure the depth of water
by sending a pressure wave from the base to the surface of the
water and note the time until theechoback from the base air.Adapun
basic usability ofechosounderthat is determining the depth of the
waters by sending a pressure wave from the base to the surface of
the water and note the time until theechoback from the bottom of
the water.
Figure 1.Echosounder Working PrincipleSource:
http://www.dosits.orgUltrasonic pulses, which is an ultrasonic
signal with a frequency of approximately 41 kHz as many as 12
periods, is sent from the transmitter Ultrasonic.When the pulse of
the object barrier, the reflected pulse, and received back by
Ultrasonic receiver.By measuring the time interval between pulses
transmitted and reflected pulse is received, the distance between
the measuring device and an obstacle can be calculated.
Figure 2.Data Depth results Echosounder useSource:
http://venus.uvic.ca2. Sonar(SoundNavigation AndRanging)Sonar(Sound
Navigation And Ranging)is a form of acoustic signals emitted and
received reflections of objects in water (such as fish or
submarines) or from the seabed.When the acoustic wave moves
vertically to the seabed and back, the time required is used to
measure water depth.Multibeamsonar is a hydro-acoustic instruments
which use the same principle witha single beam,but the difference
lies in the amount ofbeamthat emits more than one in a single
transmit .
Figure 3.Multi SonarSource: http://oceanexplorer.noaa.gov3.
Seismic SurveyOil and gas exploration process was originally done
by conducting a seismic survey is to look for a job in oil and gas
in the lower layers of the earth exactly in the sea area by mapping
the underwater layers using seismic waves.Seismic work was
conducted in the seismic vessel and to be able to map the
underwater layers required two things: the need for a source of
vibration(water gun)and the need for a recorder that can accept a
source of vibration(Hidrophone).The principle works is by firing in
waveform vibration of air(water gun)to the seabed, after arriving
at the sea floor and then the reflected vibration, and vibration
recaptured byhidrophoneas vibration recorder.The tools used in this
survey is the C-Nav GPS andGyro Compassfor boat positioning and
navigation purposes, Streamer cable that looks like a set up then
ditarikoleh streamer seismic vessel which
containsHidrophone(vibration recording device), ADC(Analog to
Digital converter),and abirdwhose role is to set the position and
depth ofthe streamer,and awater gunthat serves as the source of
vibration.
Figure 4.Principles of Marine Seismic Survey WorkSource:
http://rovicky.files.wordpress.comD. CONCLUSION
Figure 5.Topography underwater hydrographic
surveySource:http://www.nauticalcharts.noaa.govOf hydro-acoustic
technology described above obtained a conclusion that hydrographic
surveys using hydro-acoustic technology plays an important role in
various processes of oil and gas natural resources utilization in
the sea.More precisely, hydrographic survey was instrumental in the
exploration of oil and natural gas in the sea where the
hydro-acoustic technology with the use of the theory of sound
propagation in an intermediate field (in this case water) can be
used to map the bottom of the sea surface(sea bed mapping).The
results of the data obtained using hydro-acoustic technology
through hydrographic surveys, when combined with the data from
thesub-bottom profilers,will obtain a complete map of the sea floor
and detailed.Complete seabed map and detailed can be used to
support penginterpretasian geological structures under the seabed
and may then be used to search for minerals under the seabed.From
the results it anyway we can find out what are the natural
resources found on the seabed including the natural resources of
oil and gas.From it we draw the conclusion that all hydrographic
surveys bergunauntuk pemetaandan provide spatial data as a spatial
reference in the planning process of utilization and management of
oil and gas at sea.