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Geol 415

Petroleum GeologyGeology of Petroleum: An Overview

Lecture # 1

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Petroleum Geology

Introduction

Exploration for HC

Source Rocks

HC Generation & Maturation

HC Migration

Seal or cap rocks

Traps Reservoirs

Petroleum in Saudi Arabia

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Petroleum Geology

Petroleum geology comprises those

geological disciplines which are of greatest

significance for the findingand recoveryof

oil and gas

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6.HC GENERATION AND MATURATION

7. SOURCE ROCKS

5.PRIMARY HC MIGRATION

4.SECONDARY HC MIGRATION

3.SEAL OR CAP ROCK

2.TRAP

1.RESERVOIR

Seven important factors in forming petroleum accumulation

Data

LogicalOrd

er

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Geological Map of Saudi Arabia

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Stratigraphic cross-section across the Arabian shelf

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HC Exploration: Geophysical Seismic Survey

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Wire line log correlation of Arab Formation offshore Abu Dhabi

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Evolution of Exploration Concepts & Techniques

New advances in exploration technology is remote sensing from satellite

from surface geochemical & geophysical methods, and identification of

gas micro seepsand electrical conductivity of rocks above oil

accumulation

Petroleumis attributed to two origins: inorganic and organic.

Chemists and astronomers argued for an organic originsometime

igneous, sometimes extraterrestrial, or a mixture of both

Most petroleum geologists believe that petroleum forms fromthe

diagenesis of buried organic matter, note that it is indigenous to

sedimentary rocks rather than igneous one

Chemical analytical techniquesallowed petroleum source rocksto be

studied and identify potential source, tendency to generate oil or gas

and their level of thermal maturation

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Evolution of Exploration Concepts & Techniques

Commercial oil accumulation requires five

conditions:

1. Organic rich source rocksto generate the oil and/or gas

2. The source rocks must have been heated sufficientlyto yield

petroleum

3. There must be reservoir, porous to contain the HCand

permeable to permit fluid flow

4. The reservoir must be sealed by an impermeablecap rock to prevent the upward escape of petroleum to the earths surface

5. Source, reservoir, and sealmust be arranged in such a way as to trap

the petroleum

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Qusaiba Formation: Main Organicrich Source Rock

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Sandstone & shale sequences

Source Generation Migration Trap/Seal Reservoir

shale

sandstone

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Petroleum ExplorationReservoir

Trap

Seal or Cap Rock

Secondary Migration

Primary Migration

Hydrocarbon

Generation

And Maturation

Source

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Relationship of Petroleum Geology to Science

1. Petroleum geology is the application of geology to the exploration and production of oil and gas

2. Geology itself is firmly based on chemistry, physics, and biology and involves

the application of essentially abstract concepts to observed data (Fig 3).

3. The application of chemistry to the study of rocks ( geochemistry) has many

uses in petroleum geology

4. Detailed knowledge of the mineralogical compositionof rocks is important at many levels

5. Mineralogy of reservoir enables estimates to be made of the rate at which

they may los porosity during burial

6. Mineralogy is essential for accurate interpretation of geophysical well logs

through reservoirs

7. Chemistryof pore fluids and their effect on the stability of minerals can be used to predict porosity

8. Organic chemistry used in analysis of oil and gas study of diagenesis of plant

and animals tissues in sediment and the way in which the resultant organic

compound, kerogen, generates petroleum.

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The relationship of petroleum geology to the pure sciences

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Relationship of Petroleum Geology to Science

1. The application of physics to the study of rocks(geophysics) is

very important in petroleum geology

2. Geophysics makes a major contribution to understanding of the

earth's crust (plate tectonics) to the genesis and petroleumpotential

of sedimentary basins

3. Physical concepts are required to understand folds, faults, and

diapirs, and their role in oil entrapment

4. Magnetic, gravity and seismicsurveys are powerful in finding potential petroleum traps

5. Wireline well logs are effective toolin evaluating any finds interms of

lithology, porosity and petroleumcontent of a reservoir

Relationship of Biolog to Petrole m Geolog

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Relationship of Biology to Petroleum Geology

1. Biology is applied though the study of fossil, establishing

biostratigraphic zonesand regional stratigraphical correlation

2. Study of relationship between organisms and their environments

(ecology)is also important in petroleum geology

3. Carbonate sediments and reefs in particular can only be studied

with the aid of detailed knowledge of the ecology of modern faunaand flora

4. Biochemistryis important in studying the transformation of plant and

animals tissues into kerogen during burial and the generation of oil

and gas

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18/23Ranges of some well-known index fossils of the geologic record

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Petroleum geology & Petroleum Exploration and Production

1. Petroleum geologyis only one aspects of petroleum exploration

and production

2. Petroleum explorationnow involves integrated teams of people

3. The teams posses a wide range of professional skills(Fig 1.4)

4. These skills include political & social skills expertise which

involved in acquisition of prospective acreage

5. Geophysical surveyingis involved in preparing the initial data

on which leasing and, later, drilling recommendations are base

6. Geological conceptsare applied to the interpretation of the

geophysical dataone they have been acquired and processed

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Fig 1.4. Petroleum geology is part of a continuum of displine employed in exploration &

production of oil & gas. Geophysics now extends beyond the beginning of production.

Repeated seismic surveys can monitor the migration of fluid interfaces within fieldsduring their productive lifetime (4 D seismic)

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Petroleum geology & Petroleum Exploration and Production

7.Once an oil well has been drilled, the engineering aspects ofthe discovery need appraisal

8.Petroleum engineering is concerned with establishing the

reservesof a field, the distribution of petroleum within the

reservoir, and the most effective way of producingit

9. Petroleum geology lies within a continuum of disciplines,

beginning with geophysics and ending with petroleum

engineering

10. These disciplines overlap both in time and subject matter

(Fig 1.5)

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Fig 1.5 Flow chart showing how petroleum geology is only one aspect of

petroleum exploration & production, and how these enterprises themselves

are part of a continuum of events subjected to various constraints andexpedited by many disciplines

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Petroleum geology & Petroleum Exploration and Production

10. Underlying this sequence of events (Fig 1.5) is the control

of economics

11. Every stage from leasing to drilling, to productionand

enhanced recoveryis monitored by accountants and

economist.

12. Activities in petroleum exploration and production

accelerates and decelerates when oil prices increase or

decrease.