Porosity Quality & Carbonate vs. Siliciclastic Porosity

Excellent porosity quality

>20% pores

Good porosity quality

10-20% pores

Poor porosity quality

<5% pores

Carbonate (Primary porosity)

Primary porosity often ranges from 40-70%.

Siliciclastic (Primary porosity)

Primary porosity often ranges from 25-40%.

Carbonate (Ultimate porosity)

Ultimate porosity often approaches 0.

Siliciclastic (Ultimate porosity)

Commonly half or more of primary porosity.

Carbonate (Pore type)

Primary porosity is commonly interparticle but can have intraparticle pores.

Siliciclastic (Pore type)

Almost completely interparticle.

Carbonate (Pore origin)

Highly variable due to continuous, post-depositional alteration of the rock.

Siliciclastic (Pore origin)

Almost completely remnant of primary porosity.

Carbonate (Pore size)

Pore diamter and throat size commonly show little or no relation to sediment article size or sorting.

Siliciclastic (Pore size)

Closely related to sediment particle size and sorting.

Carbonate (Pore shape)

Varies according to intensity of diagenetic alteration.

Siliciclastic (Pore shape)

Strongly dependent on particle shape

Carbonate (Pore uniformity)

Uniformity of pore size, shape, and distribution ranges from uniform to highly heterogeneous, even with a particular rock type.

Siliciclastic (Pore uniformity)

Commonly uniform within a homogenous body.

Carbonate (Fractures)

Great importance in reservoir properties.

Siliciclastic (Fractures)

Generally, not of major importance.

Carbonate (Visual porosity)

Estimates range from fairly reliable to poor.`

Siliclastic (Visual porosity)

Estimates are usually fairly reliable.

Carbonate (Porosity/Permeability)

Relationship depends on pore types.

Siliciclastic (Porosity/Permeability)

Relatively consistent and depends on particle size and sorting.