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.