Internship Ppl

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1. PAKISTAN PETROLEUM LIMITED 1 Name: Osama Bin Raees Department: Exploration Department Position: Internee (Geophysicist) Institution: Bahria University Karachi Campus Internship Duration: 18th January 2016 – 14th February 2016 INTERNSHIP REPORT Submitted to: Mr. Syed Muhammad Tauqeer (Manager Exploration) 2. PAKISTAN PETROLEUM LIMITED 2 Acknowledgment The internship opportunity I had with Pakistan Petroleum Limited was a great chance for learning and professional development. Therefore, I consider myself as a very lucky individual as I was provided with an opportunity to be a part of it. I am also grateful for having a chance to meet so many wonderful people and professionals who led me though this internship period. Bearing in mind previous I am using this opportunity to express my deepest gratitude and special thanks to the Mr. Syed Muhammad Tauqeer, Manager Exploration Department, who in spite of being extraordinarilybusy with his duties, took time out to hear,guide and keep me on the correctpath and allowing me to carry out my project at this esteemed organization. I express my deepest thanks to Mr. Muhammad Shoaib Bilal, Senior Geophysicist,PPL for taking part in useful decision & giving necessary advices and guidance and arranged all facilities to make life easier. I choose this moment to acknowledge his contribution gratefully. It is my radiant sentiment to place on record my best regards, deepest sense of gratitude to Mr. Tauqeer Haider, Geophysicist PPL, Mr. Ajam Abbas, Geophysicist PPL, Mr. Haris Haleem, Geophysicist PPLfor their carefuland preciousguidance which were extremely valuable for my study both theoretically and practically. I perceive as this opportunity as a big milestone in my career development. I will strive to use gained skills and knowledge in the best possible way, and I will continue to work on their improvement, in order to attain desired career objectives. Hope to continue cooperation with all of you in the future, Sincerely, Osama Bin Raees 3. PAKISTAN PETROLEUM LIMITED 3 S.no Table Of Contents Page no. 1 Seismic Fundamentals  Seismic Waves and Its types  Seismic waves Attenuation and propagation  Huygens’ principle  Snell’s Law 4-7 2 Seismic Data Acquisition  Seismic Sources  Seismic receivers  Seismic Arrays  Seismic Acquisition Parameters  Spread Geometry 8-10 3 Seismic Data Processing  Seismic refraction  First Break  Up-Hole Logging  Digital Sampling Frequency  Frequency Filtering 10-12 4 Seismic Data Interpretation 13 5 Assignments  Stacking Chart  First break Picking  Up-hole logging  Geological Interpretation 14-18 6 Field Report 19-25 4. PAKISTAN PETROLEUM LIMITED 4 i. Seismic Fundamentals Seismic Waves: Seismic waves are messengers that conveys the information about the information about the interior of the Earth by propagating into the surface.  Body Waves: Those seismic waves which only travel through the interior of the propagating material is known as Body Waves. Characteristics of body waves are:  Travels faster  Smaller Amplitude  Short Duration  High Frequency Seismic waves Body Waves P-Wave S-Wave Surfacewaves LoveWaves Rayliegh Waves 5. PAKISTAN PETROLEUM LIMITED 5 Body waves are divided into two categories: i. P-waves ii. S-waves P-Waves: They are also called compressional or longitudinal waves because the particle motion is parallel to the direction in which waves are propagating. It can travel through any kind of material (i.e.: solid, liquid and gas) S-Waves: They are also called transverse or shear waves because the particle motion is perpendicular to the direction in which waves are propagating. It can travel only in solid material.  Surface waves: Those seismic waves which only travel along the surface and just below the surface of propagating material are called surface waves. Characteristics of S- waves are:  Large Amplitude  Low Frequency  Long duration Surface waves are divided into two types: 1. Love Waves 2. Rayleigh Waves Love Waves: Loves waves are similar to surface waves in which the particle motion is similar to S-waves but the motion is only along to the surface. Rayleigh Waves: Rayleigh waves are also called ground role because they rolls along the ground. It exhibits a retrograde elliptical motion. Its particle motion is similar to the P-waves. 6. PAKISTAN PETROLEUM LIMITED 6 Seismic Waves Propagation: As we bombarded the ground with explosive or vibrator, induces energy in a form of seismic waves that propagates into the surface of the Earth in the form of expending spherical shells. A surface associated with a propagating waves and passing through all points in the wave that have the same phase and perpendicular to the direction of propagation of waves in known as wavefront. Seismic Waves Attenuation: Seismic waves are attenuated with the depth because the loss in frequency and increase in wavelength due to which amplitudes become smaller. As seismic waves propagate away from the source the wave front becomes larger and larger due to which energy gets over spread over an even large area. As a result energy per unit become smaller. Seismic wave amplitude is proportional to the square root of energy per unit area so amplitude get smaller even at larger rate. This type of attenuation is called Geometrical spreading or spherical spreading. Another type of attenuation is due to the rock, which are not the best conductor of seismic energy. As the waves strike with the particles of the rock, some seismic energy converted into heat energy. Higher the frequency, higher the loss in energy later they arrive on seismic detectors. This type of amplitude attenuation is called In-elastic attenuation. Huygens’s Principle: This principle tells a mechanism by which a wave propagating seismic pulse lose energy with depth, stating that: “Every point on an advancing wave front is a new source of spherical wave” 7. PAKISTAN PETROLEUM LIMITED 7 Snell’s Law: When light travels from one medium to another medium, it generally bends or refract. Snell’s law of reflection states that, “The angle at which the ray is reflected is equal the angle of incidence.” < i = < r Snell’s Law of refraction tells us about the relationship between angle of incidence and and angle of refraction when the rays are passing from one medium to another medium. The portion of incident energy that is transmitted through the boundary and into the second layer with the change in direction of propagation is known as Refracted Ray. Sin <i/sin<r = V1/V2  Condition for refraction:  If the ray passes from more dense to less dense material then it bents towards the normal  If the ray passes fromless denseto more dense medium then it bents away from the normal.  The angle at which the refraction becomes 90 is called critical angle. 8. PAKISTAN PETROLEUM LIMITED 8 ii. Seismic Data Acquisition Seismic data acquisition consists of gathering and recording continuous seismic signals from seismic stations. Energy Sources: There are two basic types of energy sources, Impulsive and vibratory Source Land Marine Comments IMPULSIVE Explosives - Dynamite Ammonium Nitrate  Usually shot in drilled holes on land but rarely used as marine source. Geoflex  Shot very near at the surface Airgun  Most popular marine source Vibratory Vibroseis  Most popular land source Seismic Receivers: The instrument which detects the seismic signals are called seismic receivers. There are two types of receivers 1) Geophones 2) Hydrophones 1. Geophones: The instrument which converts ground vibrations (mechanical signals) into electrical signals is known as Geophone. It works on the principle of electromagnetic induction. Geophone 2. Hydrophones: A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Piezoelectric materials, or transducers, can convert a sound signal into an electrical signal since sound is a pressure wave. 9. PAKISTAN PETROLEUM LIMITED 9 Seismic Arrays It is the geometrical pattern in which the group of receivers and sources are arranged. The pattern may be one or two dimensional (Linear or areal) Acquisition Parameters: Following parameters values must be determined before an acquisition program can start: Line Parameters (No of lines, Orientation Of Lines, Line spacing and line length)  Source Parameters o For Explosives (No. of holes, Hole depth, Pattern) o For Vibrators (Sweep type, No of sweeps, sweep length) o For Airguns (Number and size of guns, Array design and no of Arrays) Spread Parameters o Spread Types  Off end  Source pulling or pushing spread  Split Spread  Symmetric or Asymmetric o Number of Groups o Group Interval o Maximum and minimum Offset  Fold ( Number of times CDP is imaged) 10. PAKISTAN PETROLEUM LIMITED 10 Spread Geometry When it comes to the arrangement of geophones and receivers, we have to arrange in a pattern called spread or spread geometry. Spread geometry is of two types: 1) End On Spread 2) Split Spread  End On Spread: The geometrical relation is usually required is called end on spread. Here all receivers are on one side of the source. End On Spread  Split Spread In split spread, if there is an equal numbers of receivers on each side of the source is symmetric split spread, and if there are more receivers on one side of source than the other is asymmetric split spread. SplitSpread 11. PAKISTAN PETROLEUM LIMITED 11 iii. Seismic Data Processing The purpose of seismic processing is to manipulate the acquired data into an image that can be used to infer the sub-surface structure. Seismic Refraction: Seismic refraction is a geophysical method used for investigating subsurface ground conditions utilizing surface-sourced seismic waves. The acquired data is computer processed and interpreted to produce models of the seismic velocity and layer thickness of the subsurface ground structure.  We do seismic refraction to remove the topographic variation and to determine the velocity of low velocity layer.  Low Velocity Layer (LVL) is a weathered sub surface layer which delays time in signal and produce error in the data. First Break Picking:  Events that first reach at geophones.  The first prominent wave amplitude on seismogram  Also called First arrival Redline showingFirstbreak 12. PAKISTAN PETROLEUM LIMITED 12 Up-hole Logging: Up-hole loggingisalsousedtogetLow velocitylayerinformationforstaticcorrection. Thismethodsare costlydue to drillingbutprovidesbetterresultascomparedto surface shooting method. Digital Sampling: 1. Samplingrate: The rate at whichfrequencyhasbeensampledisknownassamplingrate. 2. Samplingfrequency:The frequencyobtainedafterthe samplingisknownassamplingfrequency. Fs= 1000/sampling rate 3. NyquistFrequency:The maximumfrequencyobtainedfrom the samplingfrequencyisknown asNyquistfrequency.Itisthe half of samplingfrequency. SamplingFrequency Fn= Fs/2 4. FrequencyAliasing:The frequencywhichappearsasa low frequencygreaterthanthe Nyquist frequencyand cause errorin our data isknownas frequencyaliasing.Itdistortsthe sampling frequency. Frequency Filtering: To remove the effectof aliasingfrequencywe usedsome filters: 1. High Cut Filter:In thiswe give particularfrequencytothe recorder,the frequencyabove that givenfrequencywill notbe recorded. 2. Low Cut Filter:In thiswe give particularfrequencytothe recorder,the frequencybelow that givenfrequencywill notbe recorded. 3. Notch Filter:The removal of a particularfrequencyi.e;causesbythe presence of electricwires (55Hz) onlythat particularfrequencywill notbe recorded. 4. Band-Pass Filter:In thiswe give a range of frequencytothe recorder,the frequencyabove and belowthanthatgivenrange will notbe recorded. 13. PAKISTAN PETROLEUM LIMITED 13 iv. Seismic Data Interpretation Seismic Interpretation is the extraction of subsurface geologic information from seismic data. Reflection seismic data comprise:  Continuity of reflections indicating geologic structure.  Variability of reflections indicating stratigraphy, fluids and reservoir fabric.  The seismic wavelet.  Noise of various kinds and data defects. Seismic interpretation is the thoughtful procedure of separating these effects. Critical tothe interpretationprocessiscomparinghow horizonsandfaultstie atline intersections. Significanteffortisexpendedcorrectingmiss-tiesof faults,horizons,andsequence boundariesatevery line intersection.Inthisregard,closingthe interpretationinloopsaroundthe seismicgridisa particularlyeffectivetechnique.Onaworkstation,aquickwayto check formiss-tiesisacontourmap. Miss-tieswillbe evidentbygroupsof unreasonablecontours.Inaddition,workstationscanbe very helpful forworkingoutthe miss-tiesamongvaryingvintagesof two-dimensional databyapplyingtime and phase shiftsautomatically. Tyingall linesinboth2-D and 3-D data setsis the onlywayto reliablyconstructathree-dimensional model of the subsurface usingtwo-dimensionalimages.Tyingarounddataloopsis alsothe bestway to correlate fromfaultblockto faultblock.Otherwise,faultsmustbe jumpedusingreflectioncharacter, sequence analysis,oradditionalwell control. Afterall linesare pickedandtied,the resultsof the interpretationare then summarizedandpresented as maps.Basically,anyobservationthatcanbe made usingseismicdatacanbe postedona base map and mapped.Mapsthat are routinelymade include  Time structure mapswithfaults  Depthstructure maps  Seismicfaciesmapsforreservoir,source,orseal analysis  Thicknessmapsinferredfromseismictuninganalysis  Faultplane maps  Isochoror isopachmaps showing growthorthinningina stratigraphicinterval Seismicvelocitymapsforlithologydeterminationordepthconversion 14. PAKISTAN PETROLEUM LIMITED 14 v. Assignments: 1. STACKING CHART OBJECTIVE: To determine the fullfoldandtrapperzone. FOLD The numberof timescommondepthpointisimaged. Methodology: The general ideaof the methodistoacquire a seriesof traceswhichreflectfromthe same common subsurface mid-point.Inthe adjacentfigure source pointsare showninredandreceiverpointsingreen. The traces are thensummed(stacked) sothatsuperiorsignal-to-noise ratiotothatof the single-fold stack results.The foldof the stack isdeterminedbythe numberof tracesinthe CMP gather. Result: I coincide arecorderwith6 channelsandbyconsideringthe receiverinterval 10msource interval 10m thengot the value of full foldequal to3. NOTE The assignmentis attachedas an Annexure. 1 15. PAKISTAN PETROLEUM LIMITED 15 2. First break Picking: Objective:To pick the firstbreakand findthe thicknessandvelocityof weatheredlayer. Methodology:Iwasgiventhe chart of traces detectedonthe seismograph/geophone.Ihadto pickthe firstbreakandplottediton the T-x graph. Afterplottingthe firstbreak,Ipassedthe bestfitlinesacrossthe plottedpoints.The lineswhere intersectedisknownasCrossover distance andthe time at whichtheyinterceptisknownasinterceptedtime.ThenIfindthe slope of those bestfitlinesbyusingslope formula(y2-y1/x2-x1) thenbyinversingthe slopesIgotthe velocityof weatheredlayer. Forward Shooting Reverse Shooting T-x Graph Result: I gotthe velocityof weatheredlayer250m/sand thicknessis 6.21m. NOTE:The assignmentis attachedas an Annexure. 2 16. PAKISTAN PETROLEUM LIMITED 16 3. Up-Hole Logging: Objective:To findout the thicknessof weatheredlayer. Methodology:Iwasgiventhe up-hole logdatainwhichoffsetis2m. The data isplottedon the graph iswhichdepthison y-axisandtime onx-axis.Passthe bestfitlinesandthenfindout the thicknessof weatheredlayer. Up-hole Data Time-Depth Graph Result: I got the thicknessof weatheredlayer5.5m. NOTE The assignmentis attachedas an Annexure. 3 17. PAKISTAN PETROLEUM LIMITED 17 4. Seismic Data Interpretation OBJECTIVES The analysis of seismic data interpretation includes five steps namely as follows: 1. Reflectors identification 2. Picking & correlation of reflectors 3. Fault location 4. Time to depth conversion 5. Constructing Geo-seismic cross-sections Method 1. Identification of reflectors It is usually better to start picking reflectors by inspecting seismic sections passing through boreholes. Reflectors are identified through tying the seismic sections to the well data. Composite logs are used to determine the depth to tops of different formations. 2. Picking and correlationof reflectors Studied horizon was picked up across seismic lines after the reflector identification. 3. Fault locationdetection Faults of large vertical displacements are easily recognized, especially from the sudden stepping- out of reflections across their planes. Evaluation of Seismic Section Sirani 1. Introduction A display of seismic data along a line, such a 2D seismic profile. A seismic section consists of numerous traces with location given along the x-axis and two-way travel time or depth along the y-axis. 2. Data The data provided to me for interpretation was of Sirani field. Seismic Sections of Lines: Sirani-02, Sirani-04, Sirani-06, Sirani-08, Sirani-03 18. PAKISTAN PETROLEUM LIMITED 18 3. Procedure Identification of Horizons  Interpretation starts from bringing the control from well data known as seismic well tie.  Used wells for seismic tie.  After identification of horizons tie the line where they are intersecting each other.  Pick horizons by joining the same reflector.  Dip line and strike line interpreted in a loop.  After tying all lines note down the two way times on each Shot Point of each line.  Put the time values of all Shot Point showing in the Base Map.  Then Time-Structure map is contoured by following the same time values. NOTE The assignmentis attachedas an Annexure. 4 19. PAKISTAN PETROLEUM LIMITED 19 Field Report ( HUB BLOCK - 2D) INTRODUCTION: Explorationdepartmentof PPL arrangeda fieldvisitof 05 days for me on 2D seismicdataacquisition.As per planI arrivedin BGP base camp on 31st January2016. This crew was workinginthe HUB blockof PPL which covers an area of 418 km2 and contains 3 strike lines and 12 dip lines Mr. Sohrab Baig set my field plan in the crew as follows: 1. Day 1- Cable Crew 2. Day 2- DrillingCrew 3. Day 3- Recorder 4. Day 4- SurveyCrew HSE inductionwasgivenbythe HSE team. CABLE CREW Cable crewisdividedintodifferentsmallergroupsbecause of theirseparate workresponsibility of jobnature. a) Front Crew b) Back Crew c) Trouble Shooter Front crew Front crew is used to layout, equipment (geophones, cables). Front crew use pattern of layout which is given by client. 20. PAKISTAN PETROLEUM LIMITED 20 Responsibilities of front crew  Spacing of geophones shouldbe constant and strings proper connect with each other and with cables.  Spikes of geophones should plant properly (900 ).  All cablesandreceiverstationswhichcrossthe roadwaysoraccessroutesshouldbe buriedunder the ground.  All geophone strings should be tested immediately before connecting to cable.  Geophone pattern must be kept according to the client’s demand.  The centerof the patternmust be on the receiverpoint. More emphasis was given to normal Geophones layout geometry.  Geophone Type 30DX-10Hz  Geophone array Rectangular  Geophonesperarray 12, 1string b) BACKCREW After recording completion the geophone strings, LAUL, LAUX, batteries and cables are picked up. These cablessenttocable shopfor testingand again transfer to line for further use in data acquisition. c) TROUBLESHOOTING Active personsof the cable crewmake the seismiclineclearforrecordingandovercomethe noise factor by removingthe faultyanddisconnectedcables,geophone strings,batteries,LAUL,LAUXetc. Also try to stop people, vehicles and animals movement in the cable spread etc. Trans-cable isconnectedwithLAUX and thenfrom right,leftbothside of recorder.ActuallyTran’s cable is the only one, which is directly connected with recorder. It’s also called jumper cable. 21. PAKISTAN PETROLEUM LIMITED 21 LAUX Line Acquisition