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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 [email protected] 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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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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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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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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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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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.