Petroleum Geology

Petroleum geology is the study of origin, occurrence, movement,

accumulation, and exploration of hydrocarbon fuels.

OR

Petroleum geology is the study of Petroleum System in order to

explore the hydrocarbons

Petroleum System

A petroleum system encompasses a pod of active source rock and

all genetically related oil and gas accumulations. It includes all the

geologic elements and processes that are essential if an oil and gas

accumulation is to exist.

The essential elements of a petroleum system include the

following:

• Source rock

• Reservoir rock

• Seal rock/Trap

The essential processes includes the following:

• Generation

• Migration

• Accumulation

These essential elements and processes must be correctly placed in

time and space so that organic matter included in a source rock

can be converted into a petroleum accumulation.

Petroleum Geology as Field

Petroleum Geology is an integrated course and vast field, which

includes: geochemistry, structural geology, sedimentology,

mineralogy, fluid mechanics, mapping, volumetric calculations, risk

and uncertainty analysis, and a vast array of industrial technologies.

Basic Vocabulary

1. Petroleum (Rock Oil): naturally occurring complex of

Hydrocarbons widely distributed in the sedimentary rocks

2. Crude Oil: the liquid member of Petroleum

3. Natural gas: the gaseous member of petroleum

4. Asphalt, bitumen or Tar: the solid member of petroleum

5. Reservior: the rock containing petroleum

6. Trap: feature of rock that restrain petroleum from moving out

7. Pool: a single discrete accumulation of oil or gas in a single

reservior with a single trap

8. Field: several pools may lie vertically, side by side or overlap

laterally within a single area, areally continuous.

9. Sedimentary basin: a three dimention geological entity containing

a number of oil or gas fields.

10. Province (may be synonym of basin): several basin sharing clear

similarities but separated by barren or non basinal tracts.

11. District: a geographic concentration of fields within a province or

a basin.

12. Prospect: a small area within a basin, province or district which

may contain oil and gas but no yet has been proved to do so.

13. Play: a larger area within which drilling of prospect has been

established success and pointed the way for further drilling.

14. Conventional oil and gas: the oil and gas within a well discovered

and exploited by drilling boreholes, if other than conventional

would be unconventional.

15. Well: a hole which yield any fluid.

16. Exploratory or wildcat well: a well drilled in search of a new

accumulation of oil and gas.

17. Discovery: if exploratory well is successful then it is discovery.

18. Gushers: earlier well spur oil high into air by a strong flow when

drilled.

19. Completed well: if a discovery well shows promise of being

commercial it compeleted as a producting well.

20. Dry hole: if a well yeilds no recoverable oil or gas.

21. Logging: the processes of recording data of a well.

22. Exploration: the search for new sources of petroleum.

23. Reserves: the sources discovered by successful exploration

becomes reserves, which are portion of total resources that have

been shown to accessible and recoverable under current economic

and technologic condition.

24. Development: the process of recovering the reserves, by drilling

wells within a field and operating them successfully.

25. Operators: organization and individuals seeking or producing oil or

gas.

Basic Statistics

Measurement Units

Quantities of oil are expressed in barrels:

1 barrel = 42 US gallons=159 liters app

=34.9723158 UK (Imperial gallons)

1 Gallon(gal) = 3.7854118 US liter(L)/4.54609 UK (L)

1 cubic meter = 1,000 L= 6.37 barrels

1 metric ton = 6.8 to 7.6 barrels (dep. on sp. gravity, in UK,

USSR and others by weight)

Gas is expressed in millions of cubic feet:

1 MMcf ≈ 3.104 m3

Energy-wise, gas can be expressed in oil equivalents:

1 boe ≈ 6000 to 6500 cf

Some Numbers Number of oil and gas wells drilled to date: ~ 7 million

Percentage of wells in the USA: ~50%

Producing wells worldwide: ~ 1 million

Average production of oil wells in USA: 20 bbls/day

Average production of oil wells in Middle East: 7,000 bbls/day

Total number of producing fields: ~40,000

Total number of petroleum geologists: ~ 100,000

Total number of drill rigs worldwide: ~ 5,000

More Numbers

30.0 Gbo Annual World Oil Consumption 2008

4-8 Gbo Annual Oil Discovery Rates in 1990s-2000s

1050 Gbo Total World Oil Consumption 1860-2008

850 Gbo Conventional World Oil Reserves (1998)

1372 Gbo Conventional World Oil Reserves (BP, 2007)

2311 Gbo Conventional World Oil Reserves (USGS, 2000)

1900 Gbo World Reserves of Heavy Oil, Tar Sands,

and Oil Shales

Oil Companies 2007

Oil Companies BP (2007)

Historical Development

Prior to 1900

No “petroleum geology”; all oil discovered through

seepages

(Appalachian, California, Baku, Ploesti, Peru, Egypt,

Borneo...)

“Anticlinal theory” known but not used in practice

Many fields located in so-called “geomorphic traps”

(where the reservoir rock is truncated by a recent erosion

surface)

Drake well in 1859 first to discover oil (Pennsylvania)

1901-1924

“Anticlinal theory” put in practice with Spindeltop well in

Texas

Important discoveries in Lake Maracaibo (Venezuela), Masjid-

y-Suleiman (Iran), Trinidad, Borneo, Mexico, Oklahoma, San

Joaquin Valley, California (all USA)

Petroleum geology is “American”; foundation of AAPG

Bolivar Coastal field: First in homoclinal trap, first offshore,

first large field with heavy oil, launches

SOC becomes first major oil company

Automobiles! Gas stoves!

1925 - 1945

Important discoveries in La Paz (Venezuela), Kirkuk (Iraq;

carbonate reservoir!), numerous fields in Middle East (most

also carbonates)

Oil is organic, not inorganic; micropaleontology and organic

geochemistry developed as important tools

Technological breakthroughs: Rotary drilling, torsion

balance, gravimeter, reflection seismology, electrical well

logs, perforations; wells to 3000 meters depth (before: to

1000 m)

World Petroleum Congress founded

1945 - 1960

Drilling boom, discovery of major oil fields in Middle East,

USA, Western Canada, Russian platform

Drilling depths reach 6000 meters; gas became important

Important insights into hydrocarbon migration and

accumulation (e.g. by King Hubbert; Levorsen)

Sedimentology becomes important to understand reservoirs

“Log-normal distribution” of oil fields

1960 - 1980

Offshore drilling technology developed

Discovery of North Sea, Libya, Nigeria, Siberia, eastern

Mexico oil provinces

“Subtle traps” (e.g. North Dome in Qatar)

Vast improvement of seismic acquisition and processing;

becomes vital exploration tool. Further technological

improvements in drilling, construction, and logging

Since 1980

Passive margins plays discovered (Gulf of Mexico, West

Africa, Brazil). Deep to ultra-deep drilling technology

developed

Huge carbonate fields in intra-cratonic setting discovered

(Peri-Caspian oil province)

3-D and 4-D seismics provide volumetric and dynamic

picture of reservoirs; leads to seismic stratigraphy

Integration of petroleum disciplines; computerized

workflows

Half of the “easy oil” is produced

Why Petroleum Matters

We depend on energy: In the industrial world every person

uses the energy corresponding to about 200 human powers 24

hours per day

Fossil energy constitutes ―85% of our energy consumption

Fossil fuels have a high caloric value per volume

Fossil fuels are finite

The burning of fossil fuels has undesirable climatic

consequences

But: Energy companies are important for the economy