Five Types of Reservoir Fluids

Objectives Upon completion of this module the student should be able to: 1.

List the five types of reservoir fluids.

2.

Explain the difference between reservoir oils and reservoir gases.

3.

Explain the defining difference between black oils and volatile oils.

4.

Explain how to distinguish between black oils and volatile oils using initial production data, laboratory data, or production history.

5.

Explain how to distinguish between volatile oils and retrograde gas condensates using initial production data, laboratory data, or production history.

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Objectives Upon completion of this module the student should be able to: 6.

Locate the initial position of black oil, volatile oil and retrograde in a phase diagram. Show the shapes of liquid drop out curve vs pressure at pressures below the saturation pressure.

7.

Discuss wet gases, their occurrence in nature, the usefulness of the concept of wet gas in engineering calculations, and the identification of a wet gas using field data.

8.

Discuss the unique feature of dry gases.

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Reservoir Fluid Classification Reservoir Fluids are Classified by their Behavior During Depressurization at Reservoir Temperature and Subsequent Production •

Dry Gas – No Phase change in Reservoir or Separator

•

Wet Gas – No Phase Change in Reservoir but Liquids Form in the Separator

•

Retrograde Gas – Exhibits a Retrograde Dew Point in the Reservoir

•

Black Oil - Exhibits a Bubble Point in the Reservoir

•

Volatile Oil – Not Well Defined. It is a High Shrinkage Oil that Exhibits a Bubble Point but has a Formation Volume Factor of 2 or Greater.

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Phase Diagram of a Black Oil

Stock Tank

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Phase Diagram of a Volatile Oil

Stock Tank

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Phase Diagram of a Retrograde Gas

Retrograde

Stock Tank

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Phase Diagram of a Wet Gas

Stock Tank

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Phase Diagram of a Dry Gas

Stock Tank

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Three Gases - What Are the Differences? • Dry gas - gas at surface is same as gas in reservoir • Wet gas - recombined surface gas and condensate represents gas in reservoir • Retrograde gas - recombined surface gas and condensate represents the gas in the reservoir But not the total reservoir fluid (retrograde condensate stays in reservoir)

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The Five Reservoir Fluids

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Liq % Curve of Black Oil, Volatile Oil and Retrograde Condensate Bubble Point

Liquid %

Black Oil Volatile Oil

Retrograde Condensate Dew Point

Pressure 11 CH LAT James Jose

Phase Diagrams of Near Critical Fluids Estimated critical point

Pressure

Bubblepoint line

0% 5% 10% 15%

100 90 80 70 60

15%

50 40 35 30 25 20 15 10 5

10%

5%

Temperature 12 CH LAT James Jose

Dewpoint line

Liquid % Curve of Near Critical Fluid Bubble Point

Liquid %

Volatile Oil

Retrograde Condensate

Dew Point

Pressure 13 CH LAT James Jose

McCain’s Generalizations for Fluid Types Black oil

Volatile Oil

Retrograde Gas

Wet Gas

Dry Gas

Initial producing GOR, scf/STB

3,200

>15,000*

100,000*

Initial stock-tank liquid gravity, o API

40

>40

up to 70

No liquid

Color of stocktank liquid

Dark

Colored

Lightly colored

Water white

No liquid

Bubble point

Bubble point

Dew Point

No phase change

No phase change

Heptane-plus, mole %

> 20

20 – 12.5