SC RE Chap 1-Intro

Introduction to Reservoir EngineeringIntroduction to Reservoir Engineering

Adrian C ToddAdrian C Todd

Heriot-Watt UniversityHeriot-Watt University

DEPARTMENT OF PETROLEUM ENGINEERING

Heriot-Watt UniversityHeriot-Watt University

DEPARTMENT OF PETROLEUM ENGINEERING

History of Reservoir EngineeringHistory of Reservoir Engineering

Traced to mid 1930’sTraced to mid 1930’s

1994 Dake in ‘Practise of Reservoir Engineering.’1994 Dake in ‘Practise of Reservoir Engineering.’– ‘Reservoir Enginering shares the distinction with geology in

being one of the ‘underground sciences’ of the oil industry, attempting to describe what occurs in the wide open spaces of the reservoir between the sparse points of observation - the wells’

Integration of Reservoir EngineeringIntegration of Reservoir Engineering

Roles of the Reservoir EngineerRoles of the Reservoir Engineer

Contributing with geologists and Contributing with geologists and petrophysicists in estimation of oil-in-placepetrophysicists in estimation of oil-in-place

Determining fraction of oil-in -place that can Determining fraction of oil-in -place that can be recovered.be recovered.

Attach a time scale to the recovery.Attach a time scale to the recovery.

Day-to-day operational reservoir engineering Day-to-day operational reservoir engineering throughout the project lifetime.throughout the project lifetime.

Activities of Reservoir EngineeringActivities of Reservoir Engineering

Reserve EstimationReserve Estimation

Development PlanningDevelopment Planning

Production Operations OptimisationProduction Operations Optimisation


The reserves are the main assets of an oil The reserves are the main assets of an oil company.company.

Quantifying reserves and recovery factor is an Quantifying reserves and recovery factor is an ongoing role of the reservoir engineer.ongoing role of the reservoir engineer.

Basic data not always straightforward.Basic data not always straightforward.

Reserves can be affected by the development Reserves can be affected by the development processprocess


Geophysical Geophysical estimates from estimates from seismic interpretationseismic interpretation


Log Analysis Log Analysis estimates of porosity estimates of porosity and fluid saturationand fluid saturation


Laboratory measurements to measure Laboratory measurements to measure recoverable oilrecoverable oil

Not exclusive to reservoir engineersNot exclusive to reservoir engineers

Volumetric estimates of reserves obtained at Volumetric estimates of reserves obtained at various stagesvarious stages

STOIIP - stock tank oil initially in placeSTOIIP - stock tank oil initially in place

Reserve EstimatingReserve Estimating

Optimal Development PlanningOptimal Development Planning

Large up front investmentLarge up front investment


Requires detailed understanding of the Requires detailed understanding of the reservoir characteristicsreservoir characteristics


Various development options to be Various development options to be consideredconsidered


Rarely do reservoirs perform as predictedRarely do reservoirs perform as predicted

The reservoir engineering model has to be The reservoir engineering model has to be updated in line with the production behaviour.updated in line with the production behaviour.

Reservoir Engineering TechniquesReservoir Engineering Techniques

Traditional reservoir engineering tools were designed Traditional reservoir engineering tools were designed around slide rule and graph paper.around slide rule and graph paper.

Increasingly advanced computing capability is Increasingly advanced computing capability is enabling large ‘simulations’ to be carried outenabling large ‘simulations’ to be carried out

Available dataAvailable data

Geophysical surveysGeophysical surveys

Well logsWell logs

penetrationpenetration

cuttingscuttings

– electrical

– sonic

– nuclear

Pressure dataPressure data

Formation fluid content dataFormation fluid content data

Tools of the TradeTools of the Trade

Seismic mapsSeismic maps

Well logsWell logs

SectionsSections

Pressure Pressure measurementsmeasurements

Isopach mapsIsopach maps

Structural mapsStructural maps

Porosity mapsPorosity maps

Understanding the Understanding the geological modelgeological model

Imagination.Imagination.

Geological modelGeological model

Petroleum Reserves DefinitionsPetroleum Reserves Definitions

Subject of study for some time.Subject of study for some time.

Agreed definitions by SPE and WPC in 1996.Agreed definitions by SPE and WPC in 1996.

Recognises that not practical to have precise Recognises that not practical to have precise classification because of different forms of classification because of different forms of occurrence, wide characteristics, uncertainties occurrence, wide characteristics, uncertainties of geological environment, and evolution of of geological environment, and evolution of technologies.technologies.

Petroleum Reserves DefinitionsPetroleum Reserves Definitions

Essential that governments and industry have Essential that governments and industry have a clear assessment of quantities available and a clear assessment of quantities available and anticipated within practical time frame through anticipated within practical time frame through additional field development, technological additional field development, technological advances, or exploration.advances, or exploration.

Important that a consistent nomenclature be Important that a consistent nomenclature be used by industry to define reserves.used by industry to define reserves.

Reserves DefinitionsReserves Definitions

Reserves are those quantities which are Reserves are those quantities which are anticipated to beanticipated to be commercially recoveredcommercially recovered fromfrom known accumulationsknown accumulations from afrom a given date given date forwardforward..

Reserve estimates involve some degree of Reserve estimates involve some degree of uncertainty.uncertainty.

Uncertainty depends on reliable geological and Uncertainty depends on reliable geological and engineering data available at the time of engineering data available at the time of estimate and its interpretation.estimate and its interpretation.

Reserve UncertaintyReserve Uncertainty

Relative uncertainty expressed by placing Relative uncertainty expressed by placing reserves into two classifications.reserves into two classifications.

ProvedProved Unproved-Unproved-less certain than proved. Further less certain than proved. Further

subdived to express increasing uncertaintysubdived to express increasing uncertainty..

ProbableProbable

PossiblePossible

Methods of EstimationMethods of Estimation

DeterministicDeterministic– A single best estimate of reserves bases on

known geological, engineering, and economic data.

ProbabilisticProbabilistic– Known geological, engineering and economic

data are used to generate a range of estimates and their associated probabilities.

Proved ReservesProved Reserves

Those reserves which by analysis of Those reserves which by analysis of geological and engineering datageological and engineering data , can be , can be estimated with reasonable accuracy to be estimated with reasonable accuracy to be commercially recoverablecommercially recoverable from a from a given given date forwarddate forward from from known reservoirsknown reservoirs and and under under current economic conditions, current economic conditions, operating methods and government operating methods and government regulationsregulations..

DevelopedDeveloped and and UndevelopedUndeveloped


Deterministic methodsDeterministic methods

– reasonable certainty to express a high degree of confidence that quantities will be recovered.

Probabilistic methodsProbabilistic methods

– at least 90% probability that the quantities actually will equal or exceed the estimate.


Reserves are considered proved if Reserves are considered proved if commercial producibility is supported by commercial producibility is supported by actual production or formation tests.actual production or formation tests.

In certain cases proved reserves may be In certain cases proved reserves may be allocated on the basis of well logs and/or core allocated on the basis of well logs and/or core analysis that indicate that the reservoir is analysis that indicate that the reservoir is hydrocarbon bearing and analogous to hydrocarbon bearing and analogous to reservoirs in the same area that are producing reservoirs in the same area that are producing or have demonstrated the ability to produce or have demonstrated the ability to produce on formation tests.on formation tests.


The area of the reservoir includes:The area of the reservoir includes:

the area delineated by drilling and defined by the area delineated by drilling and defined by contacts, if any.contacts, if any.

The undrilled portions of the reservoir that can be The undrilled portions of the reservoir that can be reasonably judged as commercially productive on the reasonably judged as commercially productive on the basis of available geological and engineering data.basis of available geological and engineering data.

If no fluid contacts, lowest occurrence of If no fluid contacts, lowest occurrence of hydrocarbons controls the proved limit unless indicated hydrocarbons controls the proved limit unless indicated by definite geological, engineering or performance by definite geological, engineering or performance data.data.

Test 1Test 1

There are 950 MMstb of oil initially in place in a reservoir. There are 950 MMstb of oil initially in place in a reservoir. It is estimated that 500 MMstb can be produced. Already It is estimated that 500 MMstb can be produced. Already 100MMstb have been produced. What are the reserves?100MMstb have been produced. What are the reserves?

STOIIP is: 950 500 400 MMstb

The reserves are:

450 500400 MMstb

Test 1Test 1

There are 950 MMstb of oil initially in place in a reservoir. There are 950 MMstb of oil initially in place in a reservoir. It is estimated that 500 MMstb can be produced. Already It is estimated that 500 MMstb can be produced. Already 100MMstb have been produced. What are the reserves?100MMstb have been produced. What are the reserves?

STOIIP is: 950 500 400x MMstbx

The reserves are:

450 500400x MMstbx

Test 3Test 3

What is wrong with the following statement ?What is wrong with the following statement ?

– Reserves are those quantities which are anticipated to be recovered from a petroleum accumulation

Test 3Test 3

What is wrong with the following statement ?What is wrong with the following statement ?

– Reserves are those quantities which are anticipated to be recovered from a petroleum accumulation

AnswerAnswer

– Reserves are those quantities which are anticipated to be commercially recovered. Economics is very important aspect

EconomicsEconomics Oil and gas price ?Oil and gas price ?

Inflation?Inflation?

Future economic trends?Future economic trends?

Discount factors etc?Discount factors etc?

Answer- Answer- The current economic conditions are the basis re;- The current economic conditions are the basis re;-

pricesprices

– costs

– contracts

– government regulations

Test 4. Test 4. We have a structure in an area which we expect to We have a structure in an area which we expect to

explore. We anticipate it to contain a STOIIP of explore. We anticipate it to contain a STOIIP of 2000MMstb, and a recovery factor of 65% using primary 2000MMstb, and a recovery factor of 65% using primary recovery (30%), secondary (25%) and tertiary (10%) recovery (30%), secondary (25%) and tertiary (10%) recovery methods. What are the reserves?recovery methods. What are the reserves?

Answer:SPE/WPC - zero. Intentions are not a basis Answer:SPE/WPC - zero. Intentions are not a basis for reserves. No well has yet been drilledfor reserves. No well has yet been drilled..

Some companies will allocate potential reserves for Some companies will allocate potential reserves for internal use. Cannot be used for public or government internal use. Cannot be used for public or government figures.figures.

Requirements for proved reservesRequirements for proved reserves

MapsMaps

– from seismic and geological data.

Petrophysical logsPetrophysical logs

Well test results and rock properties from recovered Well test results and rock properties from recovered core.core.

FacilitiesFacilities

– Necessary facilities for processing and transport either in place or will be installed as backed up by formal contract

Contributions to the Proved Reservoir AreaContributions to the Proved Reservoir Area

This comes from the drilled and produced This comes from the drilled and produced hydrocarbonshydrocarbons

the definition of the gas and oil and water the definition of the gas and oil and water contactscontacts

or the highest and lowest observed level of or the highest and lowest observed level of hydrocarbons.hydrocarbons.

Also the undrilled area adjacent to the drilled Also the undrilled area adjacent to the drilled can be used.can be used.

Reserves - progression with timeReserves - progression with time

Probabilistic Representation of ReservesProbabilistic Representation of Reserves

In the deterministic approach volumes are In the deterministic approach volumes are determined by calculation of values determined by calculation of values determined for the various parameters.determined for the various parameters.

With the With the probabilistic approachprobabilistic approach statistical statistical analysis is used. e.g. Monte Carlo methods analysis is used. e.g. Monte Carlo methods

Probabilistic Representation of ReservesProbabilistic Representation of Reserves Proven - 90% probabilityProven - 90% probability

Probable - difference Probable - difference between 50 & 90%between 50 & 90%

Possible - difference between Possible - difference between 10 & 50%10 & 50%


Some measure of subjectivity. For each element there is a Some measure of subjectivity. For each element there is a probability function.probability function.


Proven = 500MMstb,Proven = 500MMstb,

Probable =740-500=240MMstbProbable =740-500=240MMstb

Possible =860-740=120MMstbPossible =860-740=120MMstb

Probabilistic Representation of ReservesProbabilistic Representation of Reserves As field is produced the shape of the curve changes. Probability As field is produced the shape of the curve changes. Probability

converted to recovery leaving less uncertainty in reserves.converted to recovery leaving less uncertainty in reserves.

Volume in-place calculationsVolume in-place calculations Volume of oil and gas in-place, V, depends on:Volume of oil and gas in-place, V, depends on:

aerial coverage of reservoir , A.aerial coverage of reservoir , A.

Thickness of the reservoir, hThickness of the reservoir, hnn..

Pore volume, expressed by porosity,Pore volume, expressed by porosity, Proportion of pore space occupied by hydrocarbon, ( Proportion of pore space occupied by hydrocarbon, (

the saturation ), 1-Sthe saturation ), 1-Sww

When expressed as stock tank volumes equation divided by Bo or Bg

n wV=Ah (1 S )

n w oV=Ah (1 S ) / B

Volume in-place calculations & ReservesVolume in-place calculations & Reserves

Where RF is the recovery factor

A - will vary according to category:proven

probable possible

n w oSTOIIP=V=Ah (1 S ) / B

FReserves = STOIIP R x

Evolution of the reserve estimateEvolution of the reserve estimate

Suggest this location



ProvedProbableProbable

Possible Possible





Deterministic perspective as indicated by top structure map

Formation Volume Factors Oil,BFormation Volume Factors Oil,Boo and Gas, B and Gas, Bgg

Formation volume factors convert reservoir Formation volume factors convert reservoir volumes to surface volumes.volumes to surface volumes.

They do not vary significantly across the reservoir They do not vary significantly across the reservoir compared to other rock related properties.compared to other rock related properties.

In some reservoirs there is a compositional In some reservoirs there is a compositional gradient which results in variations in the oil gradient which results in variations in the oil formation volume factorformation volume factor

In this case average or values measured at depth In this case average or values measured at depth would be preferredwould be preferred

Recovery FactorRecovery Factor

Proportion of hydrocarbons recovered called Proportion of hydrocarbons recovered called recovery factor.recovery factor.

Influenced by a range of properties.Influenced by a range of properties.

Rock and fluid properties.Rock and fluid properties.

Drive mechanisms.Drive mechanisms.

Formation characteristics & heterogeneityFormation characteristics & heterogeneity

Development processDevelopment process

Geometry and location of wellsGeometry and location of wells

Other Appraisal Tool - Production TestOther Appraisal Tool - Production Test

One of the moat powerful tools for reservoir One of the moat powerful tools for reservoir engineer.engineer.

Used to evaluate the characteristics of the Used to evaluate the characteristics of the reservoir under realistic conditions.reservoir under realistic conditions.

Exploration well is turned temporally into a Exploration well is turned temporally into a producing well and downhole pressure producing well and downhole pressure recorded.recorded.

Production test - Well TestProduction test - Well Test

Key aspects >

Producing interval

Downhole pressuremonitoring

Oil & Gas Flowrates

Lines

Well TestWell Test2 rate test

Initial downhole pressure

Pressure declinesin relation to flow 1

Pressure declines in relation to increased

flow 2

Well shut in and pressure

builds up

Draw down andbuild up curves

analysed to give kh

Other Appraisal ToolsOther Appraisal Tools

Nature of the Fluids - PVTNature of the Fluids - PVT important for reservoir behaviour and processing.important for reservoir behaviour and processing.

Pressure profile in a well.Pressure profile in a well.

powerful measurements to aid in reservoir structure powerful measurements to aid in reservoir structure

and dynamic continuityand dynamic continuity..

Core analysis Core analysis

a cross check for downhole measurements and a cross check for downhole measurements and

unique measurementsunique measurements..

Development PlanningDevelopment Planning An evaluation of alternative plansAn evaluation of alternative plans

Well data and Test ResultsWell data and Test Results

Reservoir mapsReservoir maps

Material BalanceMaterial Balance

Drive mechanismsDrive mechanisms

Reservoir modelsReservoir models

Techno economicsTechno economics Land developments higher degree of flexibilityLand developments higher degree of flexibility

Offshore developments limited flexibility after production system orderedOffshore developments limited flexibility after production system ordered

Reservoir mapsReservoir maps

An evaluation of alternative plansAn evaluation of alternative plans



Simple and complex modelsSimple and complex models

Displacement models for injection processesDisplacement models for injection processes

Recently, integration of geological and Recently, integration of geological and geophysical perspectives providing greater geophysical perspectives providing greater confidence in simulation modelsconfidence in simulation models


Water Drive Gas Drive

1

1

11

22

33


Production profilesProduction profiles oil, gas and wateroil, gas and water

Well requirementsWell requirements

Topside facilitiesTopside facilities

UncertaintyUncertainty

Reducing uncertainty is the key issue of the Reducing uncertainty is the key issue of the decade and not least in reservoir engineering decade and not least in reservoir engineering and its related disciplines.and its related disciplines.

More information gives less uncertainty.More information gives less uncertainty.

Collecting data costs moneyCollecting data costs money

Greater cost the delay on the project.Greater cost the delay on the project.

Tension between reservoir engineers and Tension between reservoir engineers and project engineers.project engineers.

Uncertainty - ReservoirUncertainty - Reservoir

Static propertiesStatic properties Reservoir structureReservoir structure

Reservoir properties, k, h etcReservoir properties, k, h etc

Reservoir connectivityReservoir connectivity

Impact of faultsImpact of faults

‘ ‘thief’ sandsthief’ sands


Dynamic propertiesDynamic properties Relative permeabilities etc.Relative permeabilities etc.

Fluid propertiesFluid properties

Aquifer behaviourAquifer behaviour

Well productivity ( fractures, well type, condensate Well productivity ( fractures, well type, condensate drop-out etc.drop-out etc.


Material Balance EquationMaterial Balance Equation

Water Influx

Pi

Pt

Production


Examines the pressure -volume behaviour of an Examines the pressure -volume behaviour of an entire fieldentire field

Tank model of the reservoiurTank model of the reservoiur

Engineer fits a simple model to the data and predicts Engineer fits a simple model to the data and predicts future performancefuture performance

Model gets updated to match production -history Model gets updated to match production -history matching.matching.

Reservoir simulation models comprise many Reservoir simulation models comprise many aspects of material balanceaspects of material balance


Known : Production data Np, Rp, Wp

Hydrocarbon Properties Bt, Bti, Bg, Bgi

Reservoir Properties Sw, cw, cf, m Pressure drop p

Unknown : Reserves N Water Influx We

HISTORY MATCHING

PREDICTION Known : Reserves,Water influx, Hydrocarbon properties, Reservoir properties.

Unknown : Oil & Gas production as a function of pressure drop

p t g si p p

g git ti w w fti e

ti gi w

N B B R R W

B BB B S c cNB m 1 m p W

B B 1-S

C

Production Operations OptimisationProduction Operations Optimisation The development phaseThe development phase

covers period from continuous production to covers period from continuous production to abandonment.abandonment.

When to stop a techno-economic decision.When to stop a techno-economic decision.

Best reservoir engineering data during production stage.Best reservoir engineering data during production stage.

Through production the reservoir yields its secrets.Through production the reservoir yields its secrets.

Hydrodynamic continuity revealed by post production Hydrodynamic continuity revealed by post production pressure surveys.pressure surveys.

Rise of fluid contacts needs monitoringRise of fluid contacts needs monitoring

History MatchingHistory Matching

Throughout production the comparison of the actual Throughout production the comparison of the actual performance with that predicted during appraisal stage is performance with that predicted during appraisal stage is monitored. It is during this stage that the reservoir monitored. It is during this stage that the reservoir simulation model is under examination.simulation model is under examination.

History MatchingHistory Matching.. - The update of the model to fit - The update of the model to fit actual performance.actual performance.

Clearly a model that cannot predict the past is no good for Clearly a model that cannot predict the past is no good for predicting the future!predicting the future!

Computing power is enabling integration of geological input Computing power is enabling integration of geological input with physics of flow etc. - Integrated reservoir simulation.with physics of flow etc. - Integrated reservoir simulation.


Good production records required.Good production records required.

History MatchingHistory Matching

– The update of the model in line with actual performance

Reservoir simulation success depends on Reservoir simulation success depends on detail of reservoir description and complexity detail of reservoir description and complexity of reservoir.of reservoir.

Reserve EstimatingReserve Estimating

When production data available reserves When production data available reserves estimates can be refined.estimates can be refined.

HistoricallyHistorically

– Decline curve analysis

– Material Balance Equation

Computer based reservoir simulationComputer based reservoir simulation

Decline curve analysisDecline curve analysis

Plots of production rate versus time, or Plots of production rate versus time, or production, on a variety of co-ordinate scalesproduction, on a variety of co-ordinate scales

Straight line is considered to characterise Straight line is considered to characterise behaviour and is extrapolated to predict future behaviour and is extrapolated to predict future performance.performance.

Phases of DevelopmentPhases of Development During development a number of During development a number of

phasesphases

the build up phasethe build up phase

– with predrilling may not happen

the plateau phasethe plateau phase

– the reservoir is producing at design capacity for the facilities.

The decline phaseThe decline phase

– the reservoir no longer able to produce at capacity.

– Plateau phase can be extended, eg use of artificial lift, downhole pumps or gas lift.

Economic limit - will vary according to project type

and size

Improving RecoveryImproving Recovery

Primary recoveryPrimary recovery

– recovery obtained through natural energy of the reservoir

Secondary RecoverySecondary Recovery

– energy is supplemented by injection of fluids, gas or water. To maintain or partially maintain pressure.

– Two types of oil left.

– High saturation in unswept part- by passed oil

– Lower saturation in swept part - residual oil saturation

Enhanced oil recovery, EOR.Enhanced oil recovery, EOR.

– The target for by-passed and residual oil

Three phases of recovery

Enhanced or Tertiary Recovery Enhanced or Tertiary Recovery

Improved Oil Recovery, IOR -covers all approaches to improve hydrocarbon recovery

The Uniqueness of the ReservoirThe Uniqueness of the Reservoir

Reservoir Behaviour

Reservoir Description

Reservoir Development Plan

Dynamic

Unique & Static

Early agreement to reservoir description speeds development

Leman Gas Field UK after first exploration wellLeman Gas Field UK after first exploration well

Leman Gas Field UK 10years after first exploration wellLeman Gas Field UK 10years after first exploration well

Reservoir EngineeringReservoir Engineering

A broad fundamental background of basic A broad fundamental background of basic sciences and engineering.sciences and engineering.

The behaviour of the reservoir rocks.The behaviour of the reservoir rocks.

The properties of the contained fluidsThe properties of the contained fluids

Fluid through through reservoir rocksFluid through through reservoir rocks

Reservoir drive mechanismsReservoir drive mechanisms

How things have changed !!How things have changed !!

Documents

SC RE Chap 1-Intro