1. The document describes an internship report submitted by Syed Wajih-ul-Hasnain from the University of New South Wales (UNSW) during their internship at the Reservoir Engineering Department of Pakistan Petroleum Limited (PPL) from January to February 2015. 2. The report details the revision of core reservoir engineering concepts done during the internship such as fluid properties, material balance, decline curve analysis, and use of the MBAL reservoir modeling tool. 3. Key tasks accomplished included estimating original gas in place using pressure data from 2005-2014, decline curve analysis of a volatile oil well to determine remaining reserves and life, and decline curve analysis of a wet gas well. Estimates

1. 1
Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
INTERNSHIP REPORT
Reservoir Engineering Department
(5th
Jan., 2015 to 13th
Feb., 2015)
P A K I S T A N P E T R O L E U M L I M I T E D
Submitted by:
Syed Wajih ul Hasnain
School of Petroleum Engineering
University of New South Wales (UNSW), Australia

2. 2
Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
Table of Contents
Acknowledgement ............................................................................................................................2
Introduction.....................................................................................................................................3
Reservoir Department.....................................................................................................................4
Revision and Core Concepts............................................................................................................5
Fluid Properties...................................................................................................................5
Material Balance.................................................................................................................6
Primary Recovery Mechanism................................................................................6
Decline Curve Analysis........................................................................................................8
MBAL..............................................................................................................................................10
Task Accomplished........................................................................................................................11
Conclusion......................................................................................................................................20

3. 3
Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
Acknowledgement
I am verythankful tothe PakistanPetroleumLimitedforprovidingme the opportunitytoenhance my
theoretical knowledge and experience the real time workingenvironment.
I especiallythankthe ReservoirEngineeringDepartment,PPLforgivingme the chance to learnandclear
my concepts. Iam verygrateful toMr Adil AhmedSiddiqui (seniorreservoirengineer) whoshowed
especial interestingroomingme byprovidinghisprecioustimeandbyfine tuningmyinternship
program.
Otherpeople whoIlike tothankare:
1) Dr. FareedIqbal Siddiqui (SeniorManagerReservoirEngineering)
2) M. NomanKhan(DeputyChief EngineerReservoir)
3) Mr Bilal Younus(Trainee Engineer)

4. 4
Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
1. Introduction:
The pioneerof the natural gas industryinthe country,PakistanPetroleumLimited(PPL) hasbeena
frontline playerinthe energysectorsince the mid-1950s.Asa major supplierof natural gas, PPLtoday
contributes over20 percentof the country’stotal natural gas suppliesbesidesproducingcrude oil,
Natural Gas LiquidandLiquefiedPetroleumGas.
The company’shistorycan be traced back to the establishmentof a publiclimitedcompanyinJune
1950, withmajorshareholdingbyBurmahOil Company(BOC) of the UnitedKingdomforexploration,
prospecting,developmentandproductionof oil andnatural gasresources.InSeptember1997,
BOC disinvested fromthe ExplorationandProduction(E&P) sectorworldwide andsolditsequity
inPPL to the Governmentof Pakistan(GoP).Subsequently,the governmentreduceditsholdingthrough
an initial publicofferinJune 2004. More recently, GoP furtherdisinvested its5percentshares,around
3.55 percentof the total paid-upcapital, inPPLthroughSecondaryPublicOfferingin2014. Currently,
the company’s shareholdingisdividedbetweenthe government,whichownsabout68
percent, PPLEmployeesEmpowermentTrustthathas approximately 7percent— beingshares
transferredtoemployeesunder BESOS— and private investors, whoholdnearly25percent.
PPL operatessix producingfieldsacrossthe countryat Sui (Pakistan’slargestgas
field), Adhi, Kandhkot, Chachar,Mazarani andHalaand holdsworkinginterestin fifteenpartner-
operatedproducingfields,including Qadirpurthe country’ssecondlargestgasfield.
As a majorstakeholderinsecuringasafe energyfuture forthe country, PPLpursuesanaggressive
explorationagendaaimedatenhancinghydrocarbonrecoveryandreplenishreserves. PPLtogetherwith
itssubsidiaries hasa portfolioof 47 explorationassetsof whichthe companyoperates27,including
one contract in Iraq,while 20 blocks,comprisingthree offshoreleasesinPakistanandtwoonshore
concessionsinYemen,are operatedbyjointventure partners.
Overthe years, PPL has developedareliable foundationandinfrastructure forprovidingcleanandsafe
energythroughsustainableexploitationof indigenousnatural resourceswhileadheringtobestpractices
of corporate governance andemployee healthandsafety andconstrainingthe ecological footprintof its
operations.Asaresult,MonitoringandInspection,DesignandConstruction,DrillingandWell
Engineering,JointOperations, Operational Technical SupportServices
and Projects departments, Mazarani, Adhi andKandhkotfields, Sui FieldGasCompressor
Station, Sui Production, Sui FieldEngineeringand Sui Purification standcertifiedforISO9001 Quality
ManagementSystem.
PPL hasplayeda significantrole asaresponsiblecorporate citizensince the inceptionof itscommercial
activitiesinSuibyestablishingthe Sui Model School in1957 forchildrenof workersandlocal
communities.

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
2. Reservoir Department
Reservoirengineeringdepartmentisthe core departmentof PPL.All the importantdecisionsand
fact findinginitial resultsregardingdevelopingafield,reservoirmanagementandsurveillance are
carriedout here.The staff consistsof highlyqualifiedandwell experiencedprofessionalswhoare
well qualifiedintheirjobs.
Core Responsibilities:
 Estimatingreservesandforecastingforpropertyevaluationsanddevelopmentplanning.
 Carryingout reservoirsimulationstudiestooptimizerecoveries.
 Analyzingthe propertiesof fluidtopredictfluidbehaviorandvariousphysical effects.
 Predictingreservesandperformance forwell proposals.
 Predictingandevaluatingwater-floodandenhancedrecoveryperformance.
 Developingandapplyingreservoiroptimizationtechniques.
 Developingcost-effective reservoirmonitoringandsurveillance programs.
 Performingreservoircharacterizationstudies.
 Analyzingthe economicsandriskassessmentsof majordevelopmentprograms.
 Updatingand bookingof corporate reserves

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
3. Revision of Core Concepts:
On the recommendationof SirAdil,Irevisedsome basic conceptsrelatedtoreservoirengineeringwhich
provedfruitful forthe remainingof myinternship.
3.1 Fluid Properties:
 Oil Formation Volume Factor (Bo):The liquid-phase volume atreservoirconditionsdividedby
the liquidvolume of the same sample atstandardconditions.
 Gas Formation Volume Factor (Bg):The vapor-phase volumeatreservoirconditionsdividedby
the gas volume of the same sample atstandard conditions.
 DissolvedGas-Oil Ratio(Rs): The ratio of the volume of surface gasto stock-tankoil ina
reservoirliquidphase atreservoirconditions.
 DissolvedOil-GasRatio(Rv):The ratio of volume of stocktank oil to the surface gas containedin
a reservoirvaporphase at reservoirconditions.
 Two Phase Oil Formation Volume Factor (Bto): The total volume atreservoirconditionsdivided
by itsresultingoil-phasevolume atstandardconditions.
 Two Phase Gas FormationVolume Factor (Btg): The total volume atreservoirconditions
dividedbyitsresultinggas-phase volumeatstandardconditions.
 Expansivities:Total expansionof aunitmassof oil phase betweentwopressuresatreservoir
conditions.

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
3.2 Material Balance:
The material balance conceptisbasedonthe principle of the conservationof mass.
Mass of fluidsoriginallyinplace =Fluidsproduced+Remainingfluidsinplace
This can be synthesized in the fundamental equation:
F = N* Et +We
where:
F isthe production
Et isthe expansionterm,dependingonPVTandreservoirparameters
We isthe waterinflux term
The material balance programusesa conceptual model of the reservoirtopredictthe reservoir behavior
based on the effects of reservoir fluids production and gas to water injection.
Material balance approach can be a very useful tool in performing many tasks, some of which are
highlighted below:
·Quantify different parameters of a reservoir such as hydrocarbon in place, gas cap size, etc.
·Determine the presence, the type and size of an aquifer, encroachment angle, etc.
·Estimate the depth of the gas/oil, water/oil, gas/water contacts.
·Predict the reservoir pressure for a given production and/or injection schedule,
·Predict the reservoir performance and manifold back pressures for a given production schedule.
·Predictthe reservoirperformance andwell productionforagivenmanifoldpressureschedule.
3.2.1 Primary Recovery Mechanism
Differentdrivemechanismscontribute tothe total energyrequiredtoproducesof total hydrocarbons.
1 = 𝐼𝑔𝑐 + 𝐼𝑠𝑔 + 𝐼 𝑝𝑑 + 𝐼 𝑤
Where, 𝐼𝑔 𝑐 = 𝑔𝑎𝑠 𝑐𝑎𝑝 𝑑𝑟𝑖𝑣𝑒 𝑖𝑛𝑑𝑒𝑥
𝐼𝑠𝑔 = 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑔𝑎𝑠 𝑑𝑟𝑖𝑣𝑒 𝑖𝑛𝑑𝑒𝑥
𝐼 𝑝𝑑 = 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑑𝑒𝑝𝑙𝑒𝑡𝑖𝑜𝑛 𝑑𝑟𝑖𝑣𝑒 𝑖𝑛𝑑𝑒𝑥
𝐼 𝑤 = 𝑤𝑎𝑡𝑒𝑟 𝑑𝑟𝑖𝑣𝑒 𝑖𝑛𝑑𝑒𝑥

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
Reservoirdrive index asafunctionof time shows thatin a longtime,waterdrive index contributesthe
mostenergyinoil production.
The dominantdrive mechanismforaparticularreservoircanoftenbe deduce fromthe rate of pressure
decline.

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
3.3 Decline Curve Analysis:
Decline curve analysisextrapolatespast-performance observationstoestimate futureproduction
performance.
As can be observedfromthe graphbelow,initial declinestage issufficienttocalculate future cumulative
productionandthe amountof time requiresproducingoil whichisverycrucial consideringthe amount
of moneyisat stake.
Below are the typesof curvesobserves duringthe declinecurve analysis:

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
Steps for Decline Curve Analysis
 Smooththe rate versustime data
 Calculate Dfor each time increment byusing 𝐷 = −ln (
𝑞 𝑗
𝑞 𝑗−1
) /(𝑡𝑗 − 𝑡𝑗−1)
 Estimate Di and b from1/d vs t plot
 Predictq andNp
 Match the actual andpredictedvaluesandreduce the errorbyiteration.
4. MBAL
MBAL isa reservoirmodellingtool designedtoallow forgreaterunderstandingof the currentreservoir
behaviorandperformpredictionswhile determiningitsdepletion.
Thisis the tool whichI focusedona lot.A gooduser of thissoftware can attainveryreliable resultsfrom
it.
I triedto solve all the tasksgiventome throughthissoftware toreconfirmmyresults.

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
5. Tasks Accomplished
5.1 EstimatingOGIP by calculating pressure at datum depth provided Z factor and production
data are given for the years 20005, 2007, 2011 and 2014.
K KBE
KBE, amsl
THF
THF, amsl
SeaLevel
Gauge depth,BTHF Gauge
Gauge depth (not fixed), bmsl
Datum depth,3608 ft
Datum
13.12 ft.

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
From the above schematicitcan be seenthat datumcorrecteddepthis datum depth (bmsl)-gauge
depth(bmsl),all otherdata has beenprovided.
Followingresultswerefound:
Year Average pressure at datum
2005 741.61 psia
2007 648.16 psia
2011 545.37 psia
2014 473.43 psia
Nowwe have enoughdata toutilize material balanceequationforthe calculationof OGIP.
 P/Z Vs Gp
Year Gp (TSCF) Pressure (psia) Z P/Z
2005 8.16 741.61 psia 0.9545 777
2007 8.54 648.16 psia 0.9515 681
2011 9.25 545.37 psia 0.9634 566
2014 9.84 473.43 psia 0.9675 489
From the graph OGIPwas foundtobe 12.67 TSCF

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
Note:Water influxwas consideredto be negligible hence itseffectwasnot included
 F Vs Eg
Almostsimilarresultswere foundbythismethodaswell. 12.722 TSCF OGIP
 MBAL
By utilizingMBALthe resultwasfoundtobe 12.32 TSCF whichconfirmsthe calculations
y = -168.69x + 2138
0
500
1000
1500
2000
2500
-2.00 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
P/Z
GP
y = 12722x + 290.51
0.00
10000.00
20000.00
30000.00
40000.00
50000.00
60000.00
70000.00
0 1 2 3 4 5 6
F
Eg
F vs Eg

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
5.2.1 Decline-Curve Analysis for a Volatile-Oil Well
Productionrate, cumulative productionandtime wasgiven.Usingdecline curve analysisits
remaininglifeandremainingreserveswere calculatedwitheconomiclimitgivenas20 stb/day
Withoriginal datafollowingDi andbwere found

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
b= 0.4269 Di= 0.60485
Afterthat errorwas reducedbyiterationhence predictedcurvesthatwere suitable withthe actual
curveswere:
Followingresultswerefound:
b= 0.6 Di= 1.51 Reservesremaining(Np) = 311.893 MSTB Life remaining= 19.64 yrs
y = 0.4269x + 1.6533
0
2
4
6
8
0 2 4 6 8 10 12
1/D
time
1/D VS Time
0
0.5
1
1.5
2
2.5
3
3.5
0
1000
2000
3000
4000
5000
6000
0 10 20 30 40
OILRATE(STB/DAY)
YEAR
Actual
Predicted
Actual Oil recovery
(MMSTB)
Predicted oil
recovery

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
Similarresults were obtainbyusingMBAL.

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
5.2.2 Decline-Curve Analysis for a Wet-Gas Well
Productionrate,cumulative productionandtime wasgiven.Usingdecline curve analysisits
remaininglifeandremainingreserveswere calculated witheconomiclimitgivenas1 MMscf/day
Withoriginal datafollowingDi andbwere found
b= 0.3927 Di= 1.0021
Afterthat errorwas reducedbyiterationhence predictedcurvesthatwere suitable withthe actual
curveswere:
Followingresultswerefound:
3.959,
2.28866078
y = 0.3927x + 0.9979
0
0.5
1
1.5
2
2.5
3
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
1/D(Years)
Time (Years)
1/D VS Time
0 5 10 15 20 25 30 35
0
10
20
30
40
50
60
70
0
20000
40000
60000
80000
100000
120000
0 5 10 15 20 25 30 35
Gasrate(Mscf/day)
Time (Years)
Gas rate Predicted gas rate
Cumulative production Predicted cumulative production

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
b= 0.46 Di= 1.0021 Reservesremaining(Np) = 14.31 Bscf Life remaining= 12.00 yrs
Similarresultswere obtainbyusingMBAL.
5.2.3 Decline-Curve Analysis for a Wet-Gas Well
Productionrate,cumulative productionandtime were given.Usingdecline curve analysisits
remaininglifeandremainingreserveswere calculatedwitheconomiclimitgivenas4 STB/day
Withoriginal datafollowingDi andbwere found

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
b= 0.2097 Di= 0.2318
Afterthat errorwas reducedbyiterationhence predictedcurvesthatwere suitable withthe actual
curveswere:
Followingresultswerefound:
b= 0.27 Di= 0.286 Reservesremaining(Np) = 37.53 MSTB Life remaining= 14.19 yrs
y = 0.2097x + 4.3133
0
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12 14 16
0 10 20 30 40 50 60
0
100
200
300
400
500
600
0
50
100
150
200
250
300
350
0 10 20 30 40 50 60
Oilrate(stb/day)
time (Years)
Chart Title
Oil rate predicted oil rate
cumulative production predicted cumulative production

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Syed Wajih-ul-Hasnain [Internee] UNIVERSITY OF NEW SOUTH WALES (UNSW)
Similarresultswere obtainbyusingMBAL.
6) Conclusion
The internshipatReservoirEngineeringDepartmenthas been a good learning experience. I learnt a lot
fromthe professionalsof the pioneer Petroleum Company of Pakistan. I thank everyone for giving me
their valuable time and sharing precious knowledge with me. Learning software and working on real
problems have definitely enhanced my knowledge.
I hope this internship will help me develop my future career.