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etinPage 1Resources – Hydrocarbon Geology

Outline Rocks Oil Formation Oil Migration Traps and Reservoirs

Prof. Metin Çakanyıldırım used various resources to prepare this document for teaching/training. To use this in your own course/training, please obtain permission from Prof. Çakanyıldırım.

If you find any inaccuracies, please contact metin@utdallas.edu for corrections.Updated in Sumer 2019

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etinPage 2Rock Types

Body fat is complicated

GypsumFor this & others, see the

window case on the 1st floor Founders North building

Rock

Volcanic

Metamorphic

Sedimentary

Clastic

Chemical

Organic

Acidicpart COOHAmino

part NH2

CH2Carbon-

Nitrogen bond

C

NC

Carbon-Carbonbond

Simple amino acidGlycine NH2CH2COOH

Volcanic (Igneous) Rocks: Crystalline solid rocks from cooled down magma. Metamorphic Rocks. E.g., marble develops under high pressure Sedimentary Rocks composed of sediments (grains, mud, salts) such as

– Clastic: Collection/compaction/cementation of broken up rock pieces. – Chemical (Crystalline): Including minerals and chemical salts

» Gypsum: Calcium Sulfate Dihydrate: CaSO4.2H2O. Soft rock for artifacts from ancient times. – Organic: Calcium from animal bones can combine with organic materials (proteins).

» Proteins ← Amino acids including carbon (C), hydrogen (H), oxygen (O) & nitrogen (N).

Sandstone, sand grainsShale, mud particles

Limestone, seashellsRich in Calcite CaCO3

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etinPage 3Sedimentary Rocks and Shield

Sedimentary rock layers are on top of each other.Often sandstone is above shale which is above limestone.

Densities of these are close 1.85-2.36 tons/yard3=2.4-3.1 tons/m3

However, layering sequence of rocks on top of each other depends on depositional sequence and materials, and can also be altered by tectonic plate movements and earthquakes.

SandstoneShaleLimestoneBasement rock

Tulsa

Basement rock is either volcanic or metamorphic rock.Basement rock is on the surface in some places. Then it is called shield. Shields are rich for minerals. But do not expect gas or oil in shields.Chances of oil or gas is low in mountain areas.Search for oil in stable geological platforms that contain sedimentary rocks.

ShieldsMountainsStable platforms including sedimentary rocks

E.g., layering of rocks in

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etinPage 4

Organic – Inorganic Carbon Cycle

Plants:Such as Oak

Animals without a vertebral column:Such as insects, clams, sea urchin, worms Eaten by

CarbondioxideWater Photosynthesis

Sunlight

DecompositionBacterial Decay

Rotting

Evolution to Oil, Gas, Coal

Move up byEarthquakes Migration

Reservoir

Organic Carbon

Inorganic Carbon

Several years

> 1000 of years

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etinPage 5Contents of Crude and Refined Oil

Molecule Type Weightby %

Paraffins (Alkanes): short or long chain, C-C bond

30

Naphtenes (Cycloalkanes), circle, C-C bond

49

Aromatics (incl. Benzene), circle, C=C bond

15

Asphaltics, non-uniform, complicated

6

Post Refinery # of Carbons / Molecule Weight %Gasoline 4-10 31Kerosene 11-12 10Gas Oil 13-20 15Lubricating Oil 20-40 20Residuum 40+ 24

Alk

ane

Exam

ple:

Met

hane

Cyc

lo-A

lkan

eEx

ampl

e:C

yclo

pent

ane

Aro

mat

ic E

xam

ple:

Ort

ho-x

ylen

e

Refinery

Chains: Aliphatic Compounds

Circles: Aromatic Compounds

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etinPage 6

Oil & Gas Formation

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etinPage 7Generation of Crude Oil, Gas & Coal

1% of rocks conytain organic minerals. 90% of organic material is kerogen.

– Kerogen is a polymeric compound containing carbon, hydrogen, oxygen, nitrogen, sulfur, which are also the building blocks of organic materials. When a living organism (algae, planktons, plants, animals) dies, the body decomposes into smaller molecules which can combine under pressure/temperature to create larger molecule of kerogen.

– Kerogen is not a specific chemical substance but a collection of hydrocarbons.

» Green River formations have oil shale in the from of Kerogen (in proportions of 215 Carbon; 330 Hydrogen; 12 Oxygen; 5 Nitrogen; 1 Sulphur).

– Kerogen can be cracked into smaller and lighter hydrocarbons under high temperature (thermal cracking).

10% of organic material is bitumen. – Bitumen is chemically similar to kerogen but solvable ⇒migrates easily.

OrganicMaterial

KerogenGreenishYellow

Coal

Oil & Gas

Carbon richNo Hydrogen

Carbon alongWith Hydrogen

DecompositionMaturation

Green River

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etinPage 8Van Krevelen Diagram Pre Catagenesis

Maturation of Kerogen

0.1 0.2

0.5

1.0

1.5

Ato

mic

Hyd

roge

n/C

arbo

n

Atomic Oxygen/Carbon

Diagenesis

Diagenesis

Diagenesis

Kerogen I:Mainly algal remains, anoxic conditionsH to C ratio 1.65. O to C ratio 0.06.Ratios similar to Lipids (fat, oil).

Kerogen II:Mainly marine planktonicIntermediate between I and III

Kerogen III:Other plants/animals, (sub-)oxic conditionsMainly from lignin in plantsH to C ratio < 0.84. O to C ratio 0.13.Lacking chains; Rich in circlesLow H/C ratio is similar to coal

Oak Leaves: 37% Lignin, 52% Carbohydrate;

6% Protein; 5% Lipid

Animals without a vertebral column:Such as insects, clams, sea urchin 70% Protein; 20% Carbohydrate; 10% Lipid; 0% Lignin.

Diagenesis is the initial chemical process. It can happen closer to surface at low temperatures & pressures. Diagenesis ↓ the oxygen content of the complex molecule (lateral leftward move in the graph) and yields kerogen.

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etinPage 9Van Krevelen Diagram Post Catagenesis

Maturation of Kerogen

0.1 0.30.2

0.5

1.0

1.5

H/C

O/CGraphite

Oil

Oil

OilDiagenesis

Diagenesis

Diagenesis

Kerogen I

Kerogen II

Kerogen III

Gas does not become coal

Wet gas contains less gas more liquids than dry gas.Gas is methane, liquids are more complex.Dry gas does not include liquids.

Catageneis is maturation of kerogen → oil & gas. It happens at deeper levels (high temperature & pressure). It ↓ hydrogen content (vertical / diagonal move in the graph. It yields first oil & then gas. Metagensis is further maturation of hydrocarbons into smaller gas molecules. It releases methane. The remaining residual material can further evolve to coal.

Temperature rises by ≈1 oC per 50 metres of depth. Surface has 23 oC. Oil forming temperature: 65-150 oC = 149-302 oF ≈ 150-300 oF.

Oil forming depth: 50∗ (65− 23 = 42) = 2100 metres Gas forming temperature: > 150 oC = 302 oF ≈ 300 oF .

Gas forming depth: 50 ∗ (150− 23 = 127) = 6350 metres For gas formation, >5500 metres depth suggested by Hyne.

2100

metres feet

Oil Formation

Gas Formation6350 150 oC 300 oF

≈ 7,000

≈20,800

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etinPage 10

Hydrocarbon properties

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etinPage 11API Gravity

Specific Gravity (SG) of a substance is the ratio of that substance’s density to water density. Specific gravity of lighter crude oil = 0.790/1=0.79 unitless

» API gravity of water: 141.5/1-131.5 =10» API gravity of olive oil: 141.5/0.85-131.5=34.97» API gravity of lighter crude oil: 141.5

0.790− 131.5 = 47.6≈ 48 ⇒ crude API 48.

» API gravity of light crude oil: 141.50.825

− 131.5 = 40 ⇒ crude API 40.

– Heavy oil has API 22 or less, so its density is 141.5/(22 + 131.5) = 0.922 g/cm3 or more.

– Extra-heavy oil has API less than 12 or 15, so its density is141.5/(12 + 131.5) = 0.986 g/cm3 or more. Extra-heavy oil has density ≈ water density.

API (American Petroleum Institute) gravity = 141.5SG

−131.5

Density g/cm3

Lighter crude 0.790

Light crude 0.825

Olive oil 0.850

Water 1.000

Salty water 1.025 Wat

er d

ense

st at

4 C

Easie

r to

swim

in

the

sea

than

a p

ool

0.6 1.31.0

100

10

API

Density

Transformation: Density → API toenlarge a tight interval of [0.6-1.0]

[ ]

[

[

HeavyOil

LightOil

1 cm

1 cm

1 cm3=1 milliliter

Ammonia

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etinPage 12

Characteristics of Crude Oils at Various Locations

Sulfur is corrosive so it can damage the production equipment. Sulfur is removed from oil at refineries. – Sweet (Sour) crudes have < (>) than 1% sulfur by weight. Sweet costs a few dollars more per barrel than sour.

Benchmark Crude Oils: – West Texas Intermediate (WTI) has 38-40 API and 0.3% Sulfur. – West Texas Sour has 33 API and 1.6% Sulfur.– Brent (from North Sea) has 38 API and 0.3% Sulfur– Dubai has 31 API and 2% Sulfur.

Viscosity is resistance to flow. It is important for handling / transporting oil. – Higher viscosity (in SSU or cp) implies resistance to flow.

» It can be measured by Saybolt Second Universal (SSU): the time required in seconds for a given amount of liquid to flow through a standard tube. Water has 30 SSU and Milk has 40 SSU at 68 oF. See standards ASTM 445, D2170, and D2171 from (American Society for Testing and Materials) astm.org.

» The most popular unit of viscosity in oil industry is centi poise (cp). Water ~1 cp and honey 2,000 cp.

API Gravity Sulfur % Viscosity SSU at 100 oF

Water 10 0 30

East Texas 38.4 0.33 40 (flows like milk)

Smackover, Ark 20.5 2.30 270

Loudon, Ill 38.8 0.26 45

Poza Rica, Mexico 30.7 1.67 68

Kirkuk, Iraq 36.6 1.93 42

Kern River, Cal 10.7 2.30 6700+ (does not flow)

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etinPage 13Pour Point: Solid ↔ Liquid

Melting (Solidification) Temperature Crude oil includes Paraffins, saturated hydrocarbons (i.e., carbons have a single covalent bond):

If the reservoir is hot with temperatures > 66 oC (≈ 150 oF), triacontane is in liquid form. As it is pulled, into the pipes & towards the surface it cools down. Triacontane solidifies before it reaches the surface and clogs the pipes. If the oil contains more paraffins & more carbons, its melting temperature is high.

Such oil clogs the pipes & is difficult to deal with.

The pour point of oil is the lowest temperature for solidification. Under ideal conditions, melting and solidification temperatures are the same as they are about the phase changes between solid and liquid. Arabian light has a pour point of -30 oF so it is liquid at the surface temperatures. Ekofisk oil from Norway has a pour point of 15 oF. Winter temperature in Norway

easily goes below 15 oF and the oil can solidify. In other words, Norwegian winter is so cold that it can freeze your oil!

C C C C C C C C C C C C C C C C C C C C C C C C CH

HH H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

Paraffin wax C25H52 :

Candle-like

Liquid for oC

TriacontaneC30H62

≥ 66

ParaffinC25H52

≥ 45

DecaneC10H22

≥ −35

Hexane C6H14

≥ −95

Paraffin is used as a heat absorber in house drywalls. Paraffin is in crude oil. More paraffin in oil and more carbon in paraffin ↑ melting temperature.

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etinPage 14

Porosity, Permeability, Migration, Traps

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etinPage 15

Porosity vs Permeability Porosity is the void space in the rock

– Porosity=Volume of void space/Volume of rock; generally 10-30%. Permeability is the connectedness of pores.

Porous but impermeable Porous and permeable

Liquid on this side can reachthe other side

Think of permeability as the presence of roads (for liquids) in the rock.

Clastic Sedimentary RockNot a source rock but

can serve as a pipe

Grain

Natural CementSiO2,

CaCO3

Pore

Liquid on this side cannot reachthe other side

A porous rock may be impermeable (not permeable). A porous rock may be permeable.

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etinPage 16Permeability and Flow Rate Flow rate of a liquid/gas through a rock depends on

– Intrinsic permeability (of transmitting rock) 𝜅𝜅, ↑ the rate– Viscosity of the liquid/gas 𝜇𝜇, ↓ the rate– Thickness 𝐿𝐿 of transmitting rock, ↓ the rate– Surface area 𝐴𝐴 of transmitting rock perpendicular to flow, ↑ the rate– Controllable: Pressure difference Δ𝑃𝑃, ↑ the rate– Flow rate 𝐼𝐼, in terms of a simpler form of Darcy’s law:

Higher pressurein reservoir

Lowerpressure Oil/

Gasflowsto pipe

Oil/Gasflowsto surface

Thick-ness L

Permeability 𝜅𝜅 of transmitting rock

Area A

Viscosity 𝜇𝜇

Intrinsic properties of rock and liquid/gas

Geometryof rock

Controllable pressure difference

The flow happens from high pressure region to low pressure region. [Δ𝑃𝑃 = 0] ⇒ [Flow = 0] Higher pressure difference Δ𝑃𝑃 yields higher flow rate

However, from experiments, flow rate I does not increase linearly with the pressure difference Δ𝑃𝑃 when– the speed of flow is high, which disturbs the orderly (laminar) flow of particles and causes turbulent flow,– the inertial forces (the resistance of particles to flow) are high (indicated by high Reynolds number).

Nonlinear relations between I and Δ𝑃𝑃 are suggested to salvage Darcy’s law– Quadratic, cubic relations or even higher order (power) relations by Forchheimer (in the early 20th century).– Non-linearities lead to complicated differential equations that cannot be analytically solved in a closed-form.

In practice, flow equations are solved numerically by using computational fluid dynamics software.– Comsol Subsurface Flow Module: www.comsol.com/subsurface-flow-module & www.comsol.com/video/simulating-pipe-flow-comsol-multiphysics.

Flow rate = 𝐼𝐼 = 𝐾𝐾𝜇𝜇

𝐴𝐴𝐿𝐿 Δ𝑃𝑃

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etinPage 17Permeability Increases Flow Rate

3 vertical passages 5 vertical passages 5 vertical and3 horizontal passages

5 vertical and 3 horizontalsome diagonal passages

Permeability: Streets and highways in the matter– Low permeability to Higher permeability by

» Fracturing: Introducing high pressure water & sand mixture to open passages,» Acidizing: Introducing hydrochloric acid to open passages:

In oil industry, permeability is measured in terms of flow rate of a liquid. The units of flow rate is darcy or millidarcy. 100-200 millidarcy indicates good permeability. Some permeable rocks can have 1,000 millidarcy. Tight rocks can have 0,000001 millidarcy.

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etinPage 18

Oil Flows among Rocks

Oil / gas typically moves from deeper (source) rocks toward the surface (reservoir rock).

– Expulsion of water from kerogen makes it lighter– Bitumen migrates more easily than kerogen.

– Bitumen solvable, smaller/lighter kerogen

Migration happens among rocks and within permeable rocks.

If oil contacts ground water, it will go through water and pass through it: Oil has lower density.

Depending on its viscosity, oil will migrate until it is stopped by a trap.

Source Rock, where oil matured

Reservoir Rock

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etinPage 19Traps: Onshore and Offshore

Oil migrates until it cannot, i.e., it is trapped by impermeable rock.

Trap rock (impermeable)

WaterSource rocks (permeable)

Both trap and source rocks are bent into an arch (anticline or concave shape) and oil accumulates at the crest of the arch.

A fault line can form a fault trap.

Salt flows under enough heat and pressure towards the surface. It may not reach the surface and forms an underground salt dome.Salt is impermeable and traps the oil.

Formation of Oil & Gas in a reservoir: https://www.youtube.com/watch?v=_PDOD_FEnNk

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etinPage 20Summary – Hydrocarbon geology

Immediate application of what you learnt so far:

SOM Searching for oil in the east side of the building!!! Metin took this photo in Spring 2012

Rocks Oil Formation Oil Migration Traps and Reservoirs

You may now watch Petroleum Origins www.youtube.com/watch?v=OWysYg_0I-M,www.youtube.com/watch?v=f6XWLN6GnGk and https://www.youtube.com/watch?v=9VbU0gdRHTc.

Based on - Nontechnical Guide to Petroleum Geology, Exploration, Drilling and Production. By N. J. Hyne.- Elements of Petroleum Geology. Chapter 5 of Generation and Migration of Petroleum. By R. C. Selley.- Petroleum and Reserves. Chapter 11 of Basic Petroleum Geology by P. Link. - Hydrocarbon Reserves. Chapter 3 of Oil, Gas Exploration and Production by Institut Francais du Petrole.- A. Çakmak. 2009. Analysis of Nonlinear Darcy-Forchheimer Flows in Porous Media. PhD Thesis. Dept. of Mathematics,

Texas Tech University - Private communication in 2015 with Arun Kharghoria, PhD in Petroleum Engineering.

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etinPage 21Sedimentation Process:

Weathering and Transportation

Igneous Rock: GraniteLooks glossy because of minerals

Continental MovementsEarthquakes

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etinPage 22

Case Studies: East Texas Fields and Offshore Fields

Based on - Atlas of Salt Domes in the East Texas Basin. 1984. M.P.A. Jackson and S.J. Seni. Published by Bureau of

Economic Geology.

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etinPage 23Case Study: East Texas Oil Fields

East Texas oil field is 72 km long and 8 km wide,a rectangle about 35-40 kms east of Tyler,

or a rectangle about 190 kms away from Dallas on Interstate Highway 20.

100 million years ago, shallow seas covered East Texas1. Woodbine sandstone was deposited as a horizontal

layer. Woodbine is the location; Sandstone is formation type; Similarly, Austin Chalk.

2. Other sediments covered the woodbine sandstone.3. Sabine uplift exposed the woodbine sandstone.4. Erosion removed the exposed woodbine sandstone.5. Seas deposited Austin Chalk (a limestone) and other

sediments.6. Oil migrated northeast from Eagle Ford source rock.7. Migration stopped by, cap rock, Austin Chalk.

The area was explored in the 1900s, no oil found and production companies moved to newly discovered fields in West Texas.Columbus M. Joiner acquired leases on the land, which then was used as cotton farms. He discovered oil but had financial challenges.Joiner passes the rights to Haroldson L. Hunt (originally from Illionis) in Adolphus Hotel, Dallas; see huntoil.com.Sandstone

SandstoneShale

LimestoneLimestone

Limestone

Interstate 20

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etinPage 24Mount Sylvan Salt Dome in East Texas

Source: D.H. Wood and A.B. Giles. 1982. Hydrocarbon Accumulation Patterns in the East Texas Salt Dome Province. Published by Bureau of Economic Geology.

Kaufman Co. Wills Point,Van Zandt Co.

Tyler,Smith Co.

Henderson,Rusk Co.

Texas Highway 64Prairie Creek

Mount Sylvan Dome has a circular peak to 1 km north of the Highway 64 bridge over Prairie Creek in west-central Smith county. To be specific 32o23’09” North and 95o26’55” West.The peak and base are on north-south axis and between State Highway 64 and County Road 724. The base is about 1 km north of peak.

Depth to Salt dome is about 170 metresDepth of Cap Rock 18-34 metres

Depth of Salt dome is about 6,000 m.

Southeast

Many well samples toextrapolate boundariesoff anticlines/synclines

Anticline (Syncline) is a concave (convex) shaped fold.

Faults indicate vertical platemovement.

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etinPage 25Mount Sylvan Wells in East Texas

Source: M.P.A. Jackson and S.J. Seni. 1984. Atlas of Salt Domes in the East Texas Basin. Published by Bureau of Economic Geology.

Salt

Cap Rock

SandstoneLimestone

Southeast

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etinPage 26Atlas of Salt Domes in East Texas

Source: M.P.A. Jackson and S.J. Seni. 1984. Atlas of Salt Domes inthe East Texas Basin. Published by Bureau of Economic Geology.

Mou

ntSy

lvan

Dallas

Shreveport

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etinPage 27Rocks of Alberta

Mt. Athabasca

ShreveportCascade Mountain

Cascade MountainMt. Bryce

Root of Athabasca river

Mt. Bryce

MetinMetin

This side has lighter shade Possibly interior before cracking

Side and top view of the rock piece

Side view of the rock piece

Columbia Glacier

Non-smooth sides: Violent cracking possibly by icing

Is this volcanic or sedimentary rock? Is this sandstone, shale or limestone?

Hard, firm, dense, darkLimestone used in old buildings

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etinPage 28

OffshoreContinental Shelf and Submarine Canyon

Continental Shelf: Flat shallow underwater platform that surrounds continents.

Geological structures (sedimentary rocks, faults, traps) and formation of the oil under the water is the same as they are or on land.

Geological structures extend from beach to the continental shelf. Continental shelf is shallow and extends tens of kilometers into the sea.

Slope 0.01

Coastline ContinentalSlope

Continental Shelf

SteeperSlope~0.03

Shelfdepthof 140 metres

Submarine Canyon: Canyon starting in continental shelf & extending towards the sea bottom. They often occur at river deltas.

Submarine canyons are made up by erosion of the sediments in the canyon. Sediments are deposited along the deep sea fan. Submarine canyons can contain reservoirs.

Hudson River Submarine Canyon Mississippi River Submarine Canyon

Jan 2015, Noble energy’s exploration well in Madison prospect in Block 479 turns out to have non-commercial amounts of hydrocarbons. The well has a depth of 5138 metres, is owned 60% by Noble Energy and 40% by Stone Energy.

Generic Submarine Canyon

LuciusOilfieldJan 2015, Eni starts production at Lucius oilfield in water

depth of about 2160 metres. Eni plans 5 more wells in the field, jointly owned with Freeport-McMoRan O & G.

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etinPage 29

Examples of Offshore Fields Gulf, North Sea, Eastern Mediterranean

Subsea Completions

Frigg Gas Field

Largest Offshore Field

Developing Fields

NorthSea

FieldsNorway

Scotland

Gulf of Mexico Shelf edgecontains most of the wells.

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etinPage 30

Concessions in Angola

Block 6Petrobras 40%Sonangol 20%Inter oil 10%Falcon oil 10%Initial oil 10%

Sonangol, state oil firm, grants rights in Angola. Each block is about 5000 km2. Block 6 is licensed for $305,000. Taxes: Petroleum Production Tax, Petroleum

Income Tax, Transaction Tax, Surface Fee. As an example of nepotism, Angolan President

Jose E. dos Santos appointed, June 3 2016, his daughter as head of Sonangol.