Properties of Carbonates

8/12/2019 Properties of Carbonates

1/35

QAB2033CarbonateSedimentology&Stratigraphy/Dr.BernardPierson

Carbonate

Sedimentology

& StratigraphyQAB2033

2. Properties of Carbonates


2/35

QAB20

33CarbonateSedimentology&Stratigraphy/Dr.BernardPierson

Introduction

Carbonate Oil & Gas Reservoirs

Carbonate Petroleum Basins in the World

Carbonate Platforms Carbonate Reservoirs at Outcrop

Carbonate Minerals

Carbonate Properties & Characteristics Factors Controlling Carbonate Production

& Deposition


3/35

QAB20


Oil Reservoirs in the World:

Production plus Proven Reserves

53% 47%

Middle East

Carbonates Clastics

Compiled by P.M. Harris


4/35

QAB20


33%67%

Middle East

Carbonates Clastics

Compiled by P.M. Harris

Gas Reservoirs in the World:

Production plus Proven Reserves


5/35

QAB20


Petroleum Basins with a high production

from Carbonate Reservoirs

USA : - Michigan Basin (Silurian)

West Texas (Permian)

East Texas and Gulf of Mexico (Jurassic and Cretaceous)

USSR : Timan-Pechora Basin (Devonian) Caspian (Devonian)

Canada : Western Alberta Basin (Devonian)

Italy & Sicily (Triassic and Jurassic)

Arabian gulf (Mesozoic)

Mexico (Cretaceous) Europe: North Sea (Cretaceous)

North Africa (Eocene)

Indonesia, Malaysia (Miocene)


6/35


7/35QAB20


Carbonate Platforms

Atoll in The Maldives

0 m 500


8/35QAB20


Carbonate Platforms

Atoll in French Polynesia


9/35


10/35QAB20

33CarbonateSedimentology&Stratigra

phy/Dr.BernardPierson

Present-Day Carbonate Deposits

Exuma Islands, Bahamas


11/35QAB20




Island and beach in the Maldives


12/35

QAB20



Present-Day Carbonate Platforms

Carbonate platforms in East Sabah


13/35

QAB20




Beach on Sibuan Island, Sabah, Malaysia


14/35

QAB20



Shelf Edge

G1

Miocene Carbonate Platforms

of Central Luconia, Sarawak


15/35

QAB20



Carbonate Reservoirs Exposed

at Outcrops

Cretaceous limestone sequenceexposed at Wadi Miaidin, Oman

Jurassic limestone sequence

exposed near Quriyat, OmanCarbonate reservoirs in the Arabian Gulf area

are mainly Jurassic and Cretaceous


16/35

QAB20



The Cretaceous carbonate sequence exposed at Wadi Miaidin, Oman

Contains some of the most prolific reservoirs on the Arabian Peninsula.

Carbonate Reservoirs Exposed

at Outcrops


17/35

QAB20



Carbonate Reservoirs at Outcrop

or in the Subsurface

Lower Cretaceous Rudist limestone,

Wadi Miaidin, Oman

Lower Cretaceous rudist limestone,

Subsurface (1,800 m), Abu Dhabi


18/35

QAB2033CarbonateSedimentology&Stratigra


A few Initial Remarks

on Carbonate Reservoirs

Carbonate Reservoirs are usually complexand difficult to predict.

Exposed limestones commonly look tight

and have misled many geologists inbelieving that they could not be goodreservoirs for petroleum.

Why are limestones, even those made ofthe same components, so different atoutcrop or in the subsurface? Diagenesis.


19/35



Usually boring at outcrop on first inspection....challenge todescribe. Black, grey, white or yellow

Usually lacking in sedimentary structures

Bedding may be absent or false

Under the microscope....... bigger challenge to describe Monomineralic

Numerous different grains

Some difficult to identify..................many impossible !

Complex diagenetic fabrics. Terminology...even bigger challenge to describe

Several classification schemes

Different environments of deposition each with its own terminology

Specialist techniques each with its own terminology

Are carbonates difficult ?


20/35



Carbonate Minerals

3 main minerals: CALCITE: CaCO3, rhombohedral, colorless to

white. High-Mg and Low-Mg varieties. Reacts

to acid (HCl). Chemically stable.

ARAGONITE: CaCO3, orthorhombic, brown to

colorless. Reacts to acid (HCl). Chemically

metastable DOLOMITE: CaMg(CO3)2, rhombohedral,

white to yellow. Does not react to HCl.

Chemically stable.


21/35



Calcite

1 cm1 cm

5 mm


22/35



Aragonite

1 cm

1 mm


23/35



Dolomite


24/35


Carbonate Properties

Carbonates are soluble in cold water.

Solubility decreases with increasingtemperature and salinity.

Aragonite is more soluble than calcite.

Carbonate (CO3--), bicarbonate (HCO3

-),and calcium (Ca++) ions are very abundant

in seawater. These ions are used to make carbonate

sediments components.


25/35


Characteristics of Carbonates

Carbonate sediments are created in-situ,either by carbonate-producing organismsor by chemical precipitation

Carbonate systems depend, for a largepart on tropical eco-systems

Most carbonates are produced in warm,

tropical marine waters Most carbonates are produced in shallow

marine waters


26/35


Factors Controlling

Carbonate Formation

Temperature: Tolerance of carbonate-producing

organisms to seawater temperature (23-26

C for corals)

Salinity: Tolerance level close to 36

Light: Prerequisite for life; Photosynthesis of

algae and microbial forms of life

Wind: Transport of nutrients

Water energy: circulation, tidal currents

Turbidity level: fine clastics detrimental


27/35

QAB2


Carbonate-Producing Organisms

vs. Latitude

Sea water

temperature is

determined by

latitude: warmbetween equator

and tropics,

cooling down athigher latitudes.


28/35

QAB2


40

20

20

40

0

Reefs

Shelf carbonateQAd2398c

30

30

Arabian Gulf

South China Sea

Pacific

AtollsAustralia

BahamaPlatforms

Carribbean

Distribution of Present-Day

Carbonates

Wilson (1975)


29/35

QAB2


Tolerances of Reef-Building Corals

20 25 30 35 40 45 5010

20

30

40

50

EXTREME LIMITS (Porites only)

ARABIAN GULF

ATLANTIC

&

INDO-PACIFIC

OPTIMUM

Kinsman, 1964SALINITY ()

TEMPERATUR

E(C)


30/35

QAB2


Carbonate Production vs. Light

Surface level

Light saturatedzone10-30m

Baseof photic

zone

60-80m


31/35

QAB2


Carbonate Production with Depth

Ahermatypic corals down to1000 m along with planktonic

foraminifera

Rates of production lower than intropical settings; variation with

depth not known

Sediment production from organisms

such asred algae (photophilic), bryozoa,

barnacles and ahermatypiccorals (non-photophilic)

Primarily Low-Mg andHigh-Mg Calcite

Primarily Low-Mg andHigh-Mg Calcite

Cool water

carbonate factory

Sediment productionSediment production Depth in m

500

400

300

200

100

??

Photic zone compressed in turbid water

Decrease in water temperaturecauses replacement of tropicalbiota by non-tropical biota

Sediment below base of photiczone composed primarily ofplanktonic organisms

Primarily Low-Mg and High-Mg Calcite

Primarily Aragonite

Warm water

carbonate factory

Base of phot ic zone

AfterJ

ones&

Desrochers,

1992


32/35

QAB2


Carbonate solubility with depth

The depth at which the rate

of carbonate (calcite)

sedimentation equals the

rate of carbonate dissolution

is called Calcite

Compensation Depth or

CCD

The Lysocline is the depth

at which the rate ofdissolution of carbonates

increases dramatically.

1

6

5

4

3

2

0

Depth(Km)

Increasing rate of dissolution

Pacific Ocean

dissolution

Sediment supply

lysocline

CCD


33/35

QAB2

033CarbonateSedimentology&Stratigr

aphy/Dr.BernardPierson

CCD and ACD

CCD is determined by temperature, pressure,dissolved CO2 gas content.

CCD is at about 5,000 m in Atlantic Ocean and

4,200 to 4,500 m in the Pacific Ocean, becauseof differences in dissolved CO2contents.

ACD (aragonite Compensation Depth) is at lessthan 4,200 m in the Atlantic Ocean.

Below the CCD, calcitic particles dissolve fasterthan they accumulate. Abyssal plains deeperthan 5,000 m are covered with clay and othersilica particles with no calcareous fossils.


34/35

QAB2



Wind Controls Carbonate Growth

Reef

Back-reef

Reef Apron

Lagoon

Photo by Yann Arthus-Bertrand

F t C t lli


35/35

B2



Factors Controlling

Carbonate Deposition

Water Energy: Currents, Tidal range, etc.

Atmospheric Conditions: winds, storms,..

Water Depth: Wave base, submarinecurrents

Submarine topography

Basin morphology Relative sea level fluctuations

Properties of Carbonates

Documents

Transcript of Properties of Carbonates