Ø Ratio of the volume of space to the total volume of a rock.
Ø Porosity of a rock is a measure of its ability to hold a fluid.
Ø Porosity is expressed as a percentage of the total rock which is taken up by pore space.
Total porosity
Ø the ratio of the entire pore space in a rock to its bulk volume.
Effective porosity
Ø percent of bulk volume occupied by interconnected pores spaces.
Ø A total porosity less the fraction of the pore space occupied by shale or clay
Ø In very clean sands, total porosity is equal to effective porosity.
Primary porosity
Ø porosity of the rock that formed at the time of its deposition.
Ø primary porosity of a sediment or rock consists of the spaces between the grains.
Ø Primary porosity decrease due compaction and packing of grains.
Ø Intergranular pores of clastics or carbonates.
Ø Primary porosity is less than one percent in crystalline rocks like granite.
more than 55% in some soils.
Secondary porosity
Ø develops after deposition of the rock.
Ø Vugular spaces in carbonate rocks created by the chemical process of leaching.
Ø fracture spaces formed due to stress distortion in reservoirs rocks.
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Photo from [http://cmex.ihmc.us/cmex/data/catalog/ModernGroundwater/PorosityVoids.html] |
Sent in by Ekwe Umahi Makolia, TalkOil9ja.