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Kp Seismik

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    CHAPTER I

    SEISMIC

    1.1. Background

    Refers to majors curriculum Petroleum Engineers of Balongan Oil and

    Gas AcademyThat student is obliged to executes work practice by doing

    observation to facts happened (which is relating to Petroleum

    Engineering) area industry, face practice of executed. Then this practice

    work can give opportunity to student to extend knowledge and

    understanding about petroleum engineering (especially about seismic)

    and its application and gives image of public to student about condition of

    real work.

    In increasing quality of Indonesia human resource especially past master

    in technical field, required a separate skill which ready to followcompetitive global competition. For the purpose, improvement of science

    and technology of petroleum engineering must be made balance with

    addition of direct knowledge in real work. Addition of knowledge in the real

    work for student is got by through practice work, and with the existence of

    work practice, this means science owned by student could be application.

    Work practice is one of stipulation of curriculum which must be executed

    by student of Balongan Oil and Gas Academy, to finalize D3 program.

    Fundamental principle from execution of this work practice is student does

    work relating to its study in a company where work practice of executed

    which good for increasing performance of student as past master in

    petroleum engineering. Performance of student is still unable to be

    adequate if only gets science in the college. It would be better if science

    gotten in the college is applied direct to the real work.

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    With the management of this practice work, expected the student can add

    the expertise and science which obtained in lecturing to be able and gives

    best contribution to its area either present and also in the future.

    1.2. Purpose

    1.2.1. General Purpose

    o To applies the science from the college to the real field,

    o Increases the creativity and the expertise of student.

    1.2.2. Specific Purpose

    o To determines the result of well hole measurement and knowing the

    well quality,

    o Analyses the characteristic and the character of rock under surface,

    o To find know if there were hydrocarbon or not in a zone formation.

    1.3. Practice Work Benefit

    1.3.1. For the Student

    Gives much of knowledge about its work which will be faced by

    student in the future,

    Give the opportunity to deepens science and also comprehends

    profession about technique to handle the problem in seismic

    process,

    Trains the student to think naturally in analyzing problem detailed

    then got problem solving appropriate to be applied,

    Trains the student in applying science which has obtaining of

    lecturing as according to condition of the field.

    1.3.2. For the College

    As component of evaluation in increasing quality of student a

    period of which will come,

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    Constructs good connection between the academic persons and

    institution,

    Prepares good graduate and ready to work.

    4.3. For the Company

    Braids a good connection between academic persons with the company,

    Plays tricks on student to assist solving problems faced by company, as

    according to performance of the student,

    To know how far company knowledge in finalizing the problems in field

    To more recognizes about majors Petroleum Engineering at Balongan Oil

    and Gas Academy.

    4.4. Place and Execution Time

    This practice work will be executed in company which you lead. After adapted

    with academic schedule and the research time is planned about 1 (one) month,

    but I also would be flexible to company policy.

    4.5. Practice Activity Plan Proposed

    ACTIVITY1st

    WEEK

    2nd

    WEEK

    3th

    WEEK

    4th

    WEEK

    Study Literature

    Data Collecting

    Analyses Data

    Presentation and Evaluation

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    CHAPTER II

    BASIC THEORY

    There are three kinds of method to identify a formation that is: well test (at the

    time of production), Analysis core (at the time of exploration especially to

    analyses parameter from rock in formation) and Logging (at the time of

    exploration and exploitation).

    The existence of hydrocarbon at an area is gotten from research of geology and

    geophysics (seismic, magnetic, and gravitation). To proves there are

    hydrocarbons or there is no hydrocarbon potency at an area, we needs any detail

    from the surface (which its get from geology map and measured stratigraphy)

    and from the under surface (seismic, logging, coring and cutting). Any data from

    seismic surface will be applied to get data under surface in the form of rock

    lithology. If it was indicates existence of a reservoir, then to proves there werehydrocarbons or no, we should drilling the well hole and with refer to

    measurement in well (logging) and evaluated data result of record to ascertain

    there were subterranean hydrocarbon content. Logging is processing recording

    of reservoir rock physical properties by using wireline log.

    One of factor to determine quality of well is by doing assessment the formation of

    rock (formation evaluation). Assessment of formation is a subterranean

    characteristic analysis process and rock character by using result of

    measurement of well hole (logging). Assessment of formation can be done with

    quick look (quick interpretation) or by using software. Quick look is make an

    evaluation of log at cleans zone (clean formation) quickly on the field without

    using correction of bore hole environmental impact.

    With the assessment of formation, the field will be determinable of which is the

    prospect zone to be produced, so that advantage also obtainable.

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    To ascertain there were any prospect reservoir or not in undersurface, it is

    required to measures the bore hole (logging). Logging is a measurement process

    (recording) of rock properties by using wireline log. The result of logging will be

    got curves log, it was indicating physical properties in a rock layer from deflection

    of the curves. To find know how much the prospect of the zone that we has

    measured, it need to be evaluated with quick look method or use the software.

    Assessment of formation is an analysis process of the characteristic and rock

    properties under surface by using the result of measurement well hole (logging)

    then it will be applied to determine quality of the well.

    Main purpose of the formation evaluation is:

    - Reservoir identification,

    - Allowance account of hydrocarbon in place,

    - Acquirement estimate of hydrocarbon.

    Assessment of formation can be done with interpretation in overtakes (quick

    look). The interpretation applies 3 logs, that is:

    1. Log which showing permeable zone

    - Log SP (Spontaneous Potential Log)

    - Log GR (Gamma Ray Log)

    2. Log to measuring formation resistivity:

    - IDL / LLD (Log Deep Resistivity)

    - ILM / LLM (Log Medium Resistivity)

    - MSFL (Micro Resistivity Log)

    3. Log measuring porosity:

    - Log Density (RHOB)

    - Log Neutron (NPHI)

    - Log Sonic (DT)

    2.1. Logs Which Showing Permeable Zone

    2.1.1. Log SP (Spontaneous Potential Log)

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    Log SP is difference potential value record (milivolt) thats arising from a

    mobile electrode in the bore hole and passive electrode at the surface.

    This mobile electrode passing the various rock types with different

    characteristics and its fluid contents. Difference of salinity between muds

    and fluid in rock, causes the happening of negative and positive deflection

    of SP curve that was passes a rock permeable. Deflection is formed as

    result of existence of relation between electric current with electromotive

    forces (electrochemistry and electrokinetics) in formation. At Clay layer /

    shale, SP curve shows straight line so-called Shale Base Line" (SBL). At

    the permeable formation SP curve was go away from shale base line and

    reaches constant line at permeable layer which is enough is thick.

    Deviation of SP earns right or left depends on salt rate from water

    formation and mud filtrate.

    At the application SP log is applied as follows:

    1. To identify layers which permeable,

    2. Looks for permeable layer ridges and the correlation between pits

    based on the layer ridge,3. Determines the value of water formation (Rw),

    4. Gives qualitative indication of shale layer / as clay indicator

    5. As depth reference for all log.

    2.1.1.1. SP Log work principle

    Measurement of SP log is done by the way of reducing / installs the

    equipment into hole and on the surface. Where an electrode is degraded

    into well hole then the equipment will record potential of electrics at

    various points with potential reference of electrode on the surface. Mud

    applied must have the character of conductive. Logging speed reached by

    this equipment can be reach 1500 m/hr.

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    Picture 2.1 Example of SP Log

    2.1.1.2. Excess and Insuffiency of SP log

    SP log has excesses as follows:

    1. Reacts only at permeable layer,

    2. The measurement was easy,

    3. as permeable and non permeable layer indicator,4. Can delimitate between permeable and non permeable layers.

    Insuffiency from SP log is:

    1. Doesn't work for oil base mud,

    2. Doesn't react if Rmf = Rw,

    3. Can affect electric current,

    4. The function isnt good at formation of carbonate

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    2.1.2. Log GR (Gamma Ray)

    Log Gamma Ray (GR), is the result of measurement which showing the

    level of radioactive intensity in formation. Log GR usually presented at

    first column, together with log SP curve and Caliper. Usually it has scale

    from left to right in 0-100 or 0-150 GAPI. Measurement of GR is done by

    the way of entering equipment of detector into bore hole. The formation

    which containing radioactive elements, it will transmit radioactive radiation

    where the intensity will be received by detector and noted at the surface.

    Because of radioactivity elements (pothasium) many implied in layers

    shale/clay, so that Log GR is very useful for knowing the shale content

    scale at permeable layer. draws the line of GR which having the price of

    maximum and minimum at one particular log, then the log GR curve which

    falling between the both lines is indication the existence of layer shale.

    The usefulness of log GR is:

    - Evaluation of shale content Vsh (Clay volume)

    -Determines where is the permeable layer,

    - Evaluation of radioactive mineral ore

    - Evaluation of mineral layer which is not radioactive,

    - Correlation of log at mask well

    - Correlation between wells

    2.1.2.1. Log GR work Principle

    In nature there are a lot of base material that is naturally contains

    radioactivity, that is Uranium (U), Thorium (Tho) and Potassium (K). GR

    Radioactivity comes from the third element of the radioactive; it does

    continue transmits GR in the form of high radiant energy modulations.

    This gamma ray can pierce rock and detected by gamma ray censor that

    is generally is scintillation detector. Every GR detected will generate

    electrical modulation at detector. Parameter recorded was number of

    modulations noted per set of time (count GR).

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    There are two kinds Equipment to measure GR, that is:

    1. Standard Gamma ray Tool (SGT),

    2. Natural Gamma ray Spectrometry Tool (NGT).

    SGT measures all arising natural GR, depth of investigation SGT about

    10 inches and its vertical resolution also 10 inch. SGT measures all

    arising natural GR, depth of investigation SGT about 10 inch and vertical

    its (the resolution 10 inch. NGT besides measuring all GR, also measures

    GR energy and determines concentration of 3 kinds of element

    radioactive which is ordinary at nature that is:

    Uranium (Ur235/238), Potassium (isotope 19K40), Thorium (Thorium 232)

    where the depth of it investigation is about 15 inch and it vertical

    resolution is also15 inch. the other equipment applied is Induced Gamma

    Ray Tools, this equipment attached a radioactive source transmitting

    gamma ray with high energy. As the example is log density equipment,

    like;

    Formation Density Compensated (FDC) and Litho Density Tool (LDT).

    Picture 2.2 Log Gamma Ray Principle

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    2.2. Logs Measuring Resistively Zone

    Resistively logs measures rock resistively value (solid and fluid in it) what

    needed to determines saturation value of water.

    There is three kinds of Log at resistively zone, that is:

    1. Log Deep Resistively

    Log Deep Resistively is Log which applied to measure the resistively

    at uninvited zone / not the invasion zone, its stretch around > 3 feet,

    where this log divided to become two kinds based on mud applied wile

    drilling, that is:

    - Induction Deep Log (ILD), which is applied if the mud

    used a fresh water base mud (freshwater),

    - Lateral of Deep Log (LLD), which is applied if the mud

    used a salt water mud (brine),

    2. Log Medium Resistively

    Log Medium Resistively is the log applied to measure resistively at thetransition zone which it stretch around 15-3 feet. This log consisted of

    two kinds, that is:

    - Induction Medium Log (ILM), which is applied if mud

    applied by water base mud.

    - Lateral Medium Log ( LLM ), which is applied if mud

    applied by salt water mud.

    3. Log Shallow Resistively (MSFL and SFLU)

    Log Shallow Resistively usually applies log MSFL, which applied to

    measure resistively at invasion zone by mud filtrate its spread around

    1-6 feet. At the application of all log deep curves, medium, and

    shallow is recorded to uses electrodes or coils attached at cylindrical

    mandrel, and placed approximately in centralized in well hole. Micro

    resistivity equipment uses the censor attached at tread / pad and

    forced to patch at the wall hole during survey.

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    2.2.1. Log Induction

    Log Induction is log that working on freshwater mud with formation

    resistively < 200 0hm-m, and Rmf/Rw > 20. Equipment induction

    determines resistively by the way of measuring rock conductivity. In coil

    transmitter is flown by high frequency alternating current with constant

    amplitude which will generate magnetic field in rock. This magnetic field

    generates Eddy current or Foucault current like the picture below. The

    Level of this current is equal to rock conductivity.

    Picture 2.3 Induction Measurement Principle

    It is better to applies device induction log if:

    - Rmf/Rw > 2.5- Rt < 200 ohm m

    - Layer Thick more than 10 feet

    - If the porosity under the Rw, but Rmf/Rw is still > 25 then lateralog tool

    in suggesting to be used.

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    2.2.2. Lateral Log

    Lateral device of log engineered to measure rock resistively, what drilled

    with salty mud or a real conductive mud and used to detect the zones

    which containing hydrocarbon. Besides with salty mud, lateral log will

    work carefully at formation resistively > 200 ohms - m with Rmf/Rw < 20,

    where level of bore hole > 12 inch, with thickness of layer less than 10

    feet and deep invasion > 40 inch.

    Sonde at this resistively device has buffer electrode (bucking electrode) to

    focused current survey and forces it to flowing in vertical direction to

    sonde. Current focused by this enables gauging done at rock with

    direction which more accurate. this thing is also refinement to gauging

    using the current that not focused, like ES ( Electrical Survey) the device

    former, where current survey prefer to flow in sludge, because sludge

    resistively lower than rock resistively.

    Lateral log device used for the survey in pit that mud contains having low

    resistively, and in the rock which having height resistively. Lateral logdevice in accurate figured the measures rock resistively in the range of

    0.240000 ohm-m.

    Picture 2.4 the principles of lateral Log device

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    Picture 2.5 Typical Lateralog Presentation

    2.3. Logs Measuring Porosity Zone

    To measure the level of porosity at any zone, its need to applied threekinds of log, that is:

    2.3.1 Density Log

    Log density is curve that showing density value (bulk density) pierced rock

    of bore hole, expressed in gr/cc. This density magnitude hereinafter

    applied to determine the rock porosity value. Density log together with

    neutron log applied to detect the existence of hydrocarbon.

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    Modern density equipment also measures PEF (Photo Electric Effect)

    which good for determining rock lithologi , identifies the existence of

    heavy minerals and clay evaluate.

    Picture 2.6 Work Principles Density Log

    This device works from a radioactive source from grader transmitting

    gamma ray with certain energy intensity (generally 0.66 mev) that pierces

    formation / rock.

    Rock formed from prilled of structured mineral from atoms, it consisted of

    proton and electron. Gamma ray particle will collide electron in rock,

    causing experiences reduction of energy (loose energy). The energy

    returns (after experiencing collision) will be received by detector in the

    cylinder protector witch have 3 ft length, the protector is always patches at

    wall of the well.

    Level of the energy received by detector depended from:

    - Matrix rock density

    - Rock porosity

    - The obstetrical density in rock

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    2.3.2 LogNeutron

    Porosity logs which together with density log applied to determine the

    porosity and fluid content in it. Neutron is used to determine primary rock

    porosity (rock pore space loaded by water, petroleum, or gas).

    This device works is radioactive source (Am241Be) transmits neutron

    particle into rock with amount of energy about 5 Mev.

    This device works is radioactive source (Am241Be) transmits neutron

    particle into rock with amount of energy about 5 Mev. After neutron

    particle impinges with rock, this neutron energy decreases up to level 01 -

    10 eV (level epithermal). Because the mass of hydrogen and neutron has

    the same, hydrogen atom has biggest performance to slowing down

    neutron particle compared to other atoms in rock. Then neutron particles

    that returns is catches and calculated by detector in grader. Speed of

    detector in calculating neutron particles was influenced by the existence

    of hydrogen concentration.

    Picture 2.7 Neutron Log Work Principles

    Factors having an effect on curve N are:

    - Shale / clay,

    - Rock compaction,

    - Salt water / fresh water content,

    - Oil and gas content.

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    Deflection from neutron log is increasingly dextrose of deflection of the

    curve, and then it was more consisting of hydrocarbon, furthermost

    deflection was indicating gas existence.

    2.3.3 Log Sonic

    Log sonic is applied to get the price of rock porosity as at log density and

    neutron log. Log sonic depicts the speed time of noise sent/transmitted

    into formation so is catches again by receiver.

    Voice speed through formation of rock depends on especially by rock

    matrix and distribution of its porosity. Voice speed at rock with zero

    porosity named matrix speed (tma), for a few rock:

    tma free sands = 55.5 sec / ft

    tma sandstone = 51.0 sec / ft

    tma limestone = 47.5 sec / ft

    tma dolomite = 43.5 sec / ft

    If the t price at sonic log is height, then also the price of rock porosity.

    Factors Having An In With tCurve:

    a. Shale

    Shale has big porosity even permeability comes near zero. So shale

    content will enlarge the t value.

    b. Rock compaction

    Compaction minimizes the porosity so that will reduce the t value.

    c. Water content

    Water content in rock tends to causes height t curve value.

    d. Oil Content

    Water (especially salt water) has better voice conductor character

    than oil. So the existence of oil will minimize t value.

    e. Gas Content

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    Gas isnt good voice conductor, so that it will minimize the t value.

    2.3.3.1. Sonic log application

    - To determine sonic porosity ( s )

    - To determine clays volume ( Vs )

    - To determine the lithology with the other logs

    - Timedepth relationship

    - To determine reflection coefficients

    - Mechanical properties

    - Determines quality of cement CBL VDL

    2.3.3.2. Log Sonic Work Principle

    - sonic device measures the speed of sonic voice formation,

    - Transmitter transmits a " pressure pulse" frequency 25 Hertz,

    - This modulation yields 6 wave, that is :

    a. Waving compression and waving refraction shear creeping in

    formation,

    b. Two waving direct along the length of sonde and in mud,

    c. Two surface waves along the length of well hole wall (Pseudo

    Raleigh and Stanley),

    - Speed of the waves between 4000 to 25 000 ft / sec depend on

    lithology,

    - A compressional waving creeps from transmitter via mud to

    formation, then towards in formation, then creeps in mud again to

    reach the receiver,

    - Transmitter transmits one modulations

    - a network electronic measures time from this modulation until time

    where "the first negative excursion" detected by near receiver,

    - Transmitter transmits one modulations again,

    - Measured time from the second modulation until time where the

    first negative excursion" detected by far receiver.

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    That different both the time is divided by interval receiver (span) about two

    ft then it wills yields formation transit times in microseconds / ft (sec/ft).

    A compressional transit time varies:

    - 40 sec / ft in hard formation,

    - 150 sec / ft in soft formation,

    BIBLIOGRAPHY

    1. Fathoni, Hazam Assessment of Formation and log Interpretation. Indramayu.

    Balongan Oil and Gas Academy

    2. Sudarmo, Yan. 2002 Open Hole Interpretation.

    3. Harsono, Adi Evaluation the Assessment of Formation

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