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PETROLEUM AND PETROLEUM AND FOSSIL ENERGYFOSSIL ENERGY

Dr.Ir.SudjatiDr.Ir.Sudjati Rachmat,DEARachmat,DEA

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• primarily derived from the remains of once living organisms

• most deposits formed some 500-200 million years ago

• the three major fossil fuels are coal, oil and natural gas

• currently consumed at a rate faster than produced

• very likely that fossil fuels will be depleted - the question is when?

• large resources in tar sands and oil shales

Petroleum and Fossil EnergyPetroleum and Fossil Energy

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• radiant energy – the sun is the ultimate energy source

• chlorophyll – converts sunlight into carbohydrates by combining radiant energy, cabon dioxide (CO2 ) and water (H2 O), to produce oxygen (O2 ) and carbohydrates

• important in carbon and oxygen cycles.

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The Carbon CycleThe Carbon Cycle

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Genesis of Fossil FuelsGenesis of Fossil Fuels

• Comprised of the organic (carbon-based) remnants of ancient life• anaerobic bacteria primarily responsible for breaking broke down complex

organic remains into hydrocarbon molecules - molecules of carbon and hydrogen

• Pressure and heat applied to the sediment within which organic remains are buried, and degrade (crack) the hydrocarbons into an array of molecules of various sizes. that are useful as fuel products

Plant remains + bacteria + pressure + temperature + time = hydrocarbons

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• Coal: carbonized remains of freshwater plants – swamps

•Kerogen: precursor to oil & gas, oil shale contains kerogen not oil

• Oil: saltwater algae (high in H)

• Gas: mostly methane (CH4 ) and ethane (C2 H6 )

Fossil Fuel TypesFossil Fuel Types

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The types of coal reflect the extent of biotic and thermal processing

• peat - compressed plant remains (e.g. bogs) < few thousand BTU/lb

• lignite – some plant remains < 8,300 BTU/lb, 50-55% carbon

• sub-bituminous 8,300 - 11,500 BTU/lb, 55-60% carbon

• bituminous 11,500 - 14,000 BTU/lb, 60-85% carbon

• anthracite >14,000 BTU/lb, 85-98% carbon

• graphite – pure carbon

CoalCoal

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CoalificationCoalification

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Coalification of plant debris buried at the bottom of a swamp include:

1. Aerobic decay: In the first few centimeters, active aerobic bacterial decay reduces by as much as 50%. Because the water is stagnant and the peat is almost impermeable, the bacteria soon use up all the available oxygen and die ending the first stage.

2. Anaerobic decay: Bacteria that require no oxygen continue the decay process reducing the volume further. Decay produces acids and pH decreases throughout stage one and two. When the pH get to about 4.0 it anaerobic bacteria die off. At this point the peat has changed into a black, cheesy, gel-like material. It is this material that will eventually be changed into a coal seam.

3. Bituminization: Thermal processes now finish the metamorphisis during burial of the peat by at least two or three thousand feet of sediment depending on the geothermal gradient. Once the temperature reaches 100º C chemical reactions drive off water, oxygen and hydrogen which raises the percentage of carbon. The degree to which the bituminization goes determines the coal rank.

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Coal Production and ConsumptionCoal Production and Consumption

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Coal ReservesCoal Reserves

• reserves 1.1 trillion tons (100’s or 1000’s of years)

• global production over £100 billion in 2000

• only 20-50% of seam recoverable in many areas

• high (3% S) vs low sulfur (< 1% S) coal

• Borneo coal (50+m thick, near surface, 0.06% S)

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Petroleum originates from alteration and heating of organic matter

Diagenesisambient up to ~ 50 Cbacterial decay, oxidation, dehydrationH2 O, CO2 and CH4 are expelledproduces kerogen or its precuror, humin

Catagenesis~ 50 to 250 Coil generation begins at 50 to 60 C and peaks at ~ 130 Cgas generation ~ 150 to 250 Cthermal cracking

Metagenesis> 250 Cmetamorphism - graphite generation

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thermal cracking

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Marine organic matter is a major precursor for petroleumMarine organic matter is a major precursor for petroleum

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OrganicOrganic--rich sediments can form wherever life is abundantrich sediments can form wherever life is abundant

nutrients

algal bloom

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OxygenOxygen--rich (rich (oxicoxic) ) vsvs OxygenOxygen--poor (anoxic) Waterpoor (anoxic) Water

Oxic

• most organic matter is consumed by biota in the water columnCH2 O + O2 = CO2 + H2 O

• much of the organic matter that reaches the floor is consumed by benthic organisms• accumulation and preservation a function of sedimentation rate• generally poor source sediments (H-poor, gas-prone)

Anoxic

• where the water column is stratified (e.g. temperature), bottom waters may become depleted in oxygen• organic matter in oxygen-poor water degraded by less efficient anaerobes• more organic matter sinks to the floor, where benthic critters are absent• black muds and shales (H and lipid-rich, oil prone)

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Geologic scenarios for accumulation of biogenic hydrocarbonsGeologic scenarios for accumulation of biogenic hydrocarbons

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Migration and Trapping PetroleumMigration and Trapping Petroleum• Primary migration: expulsion of petroleum from source rock into permeable carrier bed• Secondary migration: flow of petroleum within the carrier bed and into a trap• Tertiary migration: subsequent movement after intial trapping

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folded rocks - anticline

Once segregated, petroleum may segregate into hydrocarboncontituents based on relative densities

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Oil Exploration and Recovery (Drilling)Oil Exploration and Recovery (Drilling)

• major oil companies spend millions of pounds each yearon geologic exploration – includes basic science research and development

• basic oil search techniques include‘wildcat’ drillinggeology – drillholes and well logsseismic mapping of subsurface – ‘vibroseis’

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Petroleum ExplorationPetroleum Exploration

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Geophysical Application to Geophysical Application to Petroleum GeologyPetroleum Geology

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Petroleum ExplorationPetroleum Exploration-- Geophysical MethodsGeophysical Methods

• Gravity methods

• Magnetic surveys

• Seismic surveys

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-3-2-1+1

Salt2.1 gm/cm3

Corrected Gravity(Bouguer Anomaly)

UncorrectedGravity

Clastics2.4 gm/cm3

Meter

GravityValue (mgal)

Principle of Gravity SurveysPrinciple of Gravity Surveys

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Principle of Magnetic SurveysPrinciple of Magnetic Surveys

+

-

Basement

Sedimentary Basin

Magnetization

Measured

(from xxx, 19xx)

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Seismic SurveysSeismic Surveys

• The seismic tools commonly used in the oil and gas industry are 2-D and 3-D seismic data

• Seismic data are used to:– Define and map structural folds and faults– Identify stratigraphic variations and map sedimentary

facies– Infer the presence of hydrocarbons

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Weathered layer

Horizontal reference

SourceReceivers

Surface

Modified from Waters, 1981

BasicBasicSeismic Seismic PrinciplesPrinciples

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Sea bed

Boat

Cable with hydrophones

Sea Surface

Source(Airguns)

Sedimentary Layers

Incidentwaves Reflected

waves

Marine Acquisition SystemMarine Acquisition System

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Modified from Weimer and Davis,1996

Seismic Section with Log TiesSeismic Section with Log Ties

GeophysicalWell Log

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Applications of Seismic DataApplications of Seismic Data

• Make a structural model of the reservoir• Delineate and map reservoir-quality rocks• Establish gas/water contacts

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VLE

400 F

ault

00621-

-114

00

-12600

0821-

-12400

-12000

-118

00

00611-

-116

00

-12

400

-126

00

-124

00

00421-

00621-

-124

00

-122

00

-11600

-12400

-12400

-130

00

-128

00

-12600

W

N

m0 3000

0 1000ft

-11,600-12,000

-12,000-12,400

> -11,600

Top Misoa C-4 SandElevation (ft)Sea-level datum

-12,400-12,800

< -12,400O

WO

W

O

Structural Map, VLE 196 Field

N

Structural interpretationbased on 3-D seismic and well log data

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SeismicAmplitude

Mapof a

Horizon

Channels

Modified from Brown, 1996

3-D Seismic datadefine reservoir-quality,channel-fillsand deposits

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Fluid Level Boundaries on 3Fluid Level Boundaries on 3--D DataD Data

Modified from Brown, 1996

Not Interpreted Interpreted

Flat spot on seismic line indicates petroleum / water contact

Fault

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44--D Seismic SurveysD Seismic Surveys

• The “4” in 4-D seismic is time• A 4-D survey means that at least two 3-D seismic

surveys have been made at different times over the same field

• Reflection character (attributes) change through time

• These changes result from migration of the water contact in the reservoir

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Subsurface Geologic ReconstructionSubsurface Geologic Reconstruction

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•• Primary Recovery:Primary Recovery: uses only the natural energy of the reservoir – typically recovers up to 50% of reservoir oil (average ~ 20%)

•• Secondary Recovery:Secondary Recovery: involves adding energy to the reservoir by injecting water to maintain pressure and displace the oil – typically recovers about 25-45% after primary recovery (average ~ 30%)

•• Tertiary Recovery:Tertiary Recovery: other methods can recover an additional 15 – 20% of oil after primary and secondary recovery

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Oil removal can have immediate geologic effects

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Crude oil is separated into various petroleum products by the process of fractional distillation

Hydrocarbon fraction are separated in a distillation tower based on their boiling points

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Oil RefineryOil Refinery