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Introduction and

Properties of

Carbonates

Hypothesis vs.

Theory

Hypothesis

A scientific explanation that fits all available data. A

hypothesis can be tested and may be altered or

rejected as new data become available.

Theory

A hypothesis or a group of related hypotheses

that has/have withstood repeated testing and

is/are generally accepted as correct. A theory can

be disproven but cannot be proven!

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R. Michael Lloyd

1930–2011

“I am practicing the

purest form of our

science.”

Petroleum Geology

According to Mike Lloyd

Hypothesis: Develop a play (make a

map).

Test Hypothesis: Drill a well.

Revise Hypothesis: Redraw the map.

Establish a Theory: Drill a productive

well.

Disprove a Theory: Drill a dry infill

well.

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Summary

Differences Between

Carbonates and

Siliciclastics

Oil Production and Proven Reserves

Carbonate

Reservoirs

Siliciclastic

Reservoirs

Middle East

P. M. Harris

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Natural Gas Production and Proven Reserves

Middle East

P. M. Harris

Carbonate

Reservoirs

Middle

East

Silicaclastic

Reservoirs

“Carbonate

sediments are

born, not made.”

Noel James, 1984

Siliciclastic

Sediment is

Allocthonous (comes from somewhere else)

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Carbonate Sediment

is Autothonous (forms close to where deposited)

Siliclastic Sediments

and Rocks are

Composed of

Chemically Stable

Minerals

Carbonate

Sediments and

Rocks are Easily

Dissolved

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Siliclastic Rocks have

Relatively Simple

Pore Systems

Carbonate Rocks

have Complex

Pore Systems

Summary

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Carbonate Minerals

Aragonite CaCO3

Metastable

2.93 gm/cc

Calcite CaCO3

Stable

2.71 gm/cc

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Magnesian

Calcite CaCO3 with 5–24

mole % MgCO3

metastable

Dolomite (Ca, Mg)CO3

stable

2.84 gm/cc

Scholle and Ulmer-Scholle, 2003

Magnesium in Carbonate Minerals

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Summary

Modes of

Precipitation

Organic Calcium

Carbonate Precipitation

Ca2+ + 2HCO3-

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Fossiliferous Limestone

Inorganic Calcium

Carbonate Precipitation

H2O + CO2 + CaCO3

Ca2+ + 2HCO3-

Factors Affecting Inorganic Precipitation

of Solid Calcium Carbonate from Seawater

Temperature

Pressure

Salinity

Increase Temperature, Lose CO2,

Precipitate Calcium Carbonate

Decrease Pressure, Lose CO2, Precipitate

Calcium Carbonate

Decrease Salinity, Decrease Competing

Cations, Precipitate Calcium Carbonate

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Ooid Sand Shoals

Joulters Cays, Bahamas

Inorganically Mediated Precipitation:

Photosynthesis

6H2O + 6CO2

C6H12O6 + 6O2

Whitings

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Summary