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Porosity and

Permeability

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Porosity

The void spaces between grains

Can be primary or secondary

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Porosity

Porosity (%) =! volume of voids x 100! ! Total volume of rockHowever, not all porosity is effective

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Permeability

Links between pore spacesthat provide conduits forfluid flow

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Permeability

The value of permeability is governed byDarcys law

Q = K (P1-P2) AuL

Q = rate of flow

K = permeability(P1-P2) = pressure drop across sampleA = cross sectional areaL = length of sampleu = viscosity of fluid

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Permeability

The value of permeability(K) depends upon:

Number of conduits

between pores Size of conduits How straight they are

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Porosity Types

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Porosity Types

Interparticle porosity

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Porosity Types

Interparticle porosity

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Porosity Types

Intercrystalline porosity(dolomitic)

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Porosity Types

Intraparticle porosity

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Porosity Types

Moldic porosity

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Porosity Types

Vuggy porosity

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Porosity Types

Vuggy porosity

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Porosity Types

Fenestral porosity

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Porosity Types

Fracture porosityand permeability

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Porosity Types

Fracture porosityand permeability

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Porosity Types

Can have several different types ofporosity and permeability within one rock

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Porosity Types

Can have several different types of porositywithin one rock

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Porosity/Permeability and

Rock Texture

/

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Porosity/Permeability and RockTexture

In detrital rocks, porosityand permeability are afunction of rock texture,

including:

Grain shape (roundnessand sphericity)

Grain size

Sorting

Fabric (packing and grain

orientation)

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain shape

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain packing

cubic packing gives higher porosity & permeability vsrhombohedral packing

rhombohedral packing enhanced by compaction

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain size

Theoretically, should be no change in porositywith grain size, but practically porosity can

either increase or decrease with grain size

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain size

remains constant with

decreasing grain size

K increases with grain

size due to increasingsize of pore throats

/ b d R k

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Porosity/Permeability and RockTexture

& K and grain sorting

Porosity increases with

improved sorting

K increases with improved

sorting

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain sorting

Porosity increases with

improved sorting

K increases with improved

sorting

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain orientationvaries on three scales:Microscopic--the scale ofpores and pore throats

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain orientationvaries on three scales:Microscopic--the scale ofpores and pore throats

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain orientationvaries on three scales:

Mesoscopic--scale ofsedimentary structuresand beds

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain orientationvaries on three scales:

Mesoscopic--scale ofsedimentary structuresand beds

P it /P bilit d R k

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Porosity/Permeability and RockTexture

& K and grain orientationvaries on three scales:

Mapscale--scale of depositionalenvironment

R l ti hi b t it &

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Relationship between porosity &permeability

The textural controlof porosity andpermeability resultsin a relationshipbetween the two.

However, thatrelationship is notexact

R l ti hi b t it &

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Relationship between porosity &permeability

R l ti hi b t it &

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Relationship between porosity &permeability