Changes

In samples having a porosity greater than 30%, sidewall core porosity is 1 to 2% lower than conventional analysis porosity. This results from slight compaction that occurs during coring. Medium and low porosity percussion sidewall samples, especially from highly cemented rocks, display porosity that is much too high due to fracturing and grain shattering. The deviation between measured porosity and true porosity becomes greater as the actual porosity decreases. Uncertainty caused by systematic variation in sidewall core porosity relative to plug analysis values can be minimized by development of correlations between sidewall core and conventional core values.<ref name=pt05r38 /> (For more on porosity, see [[Porosity]].)

In samples having a porosity greater than 30%, sidewall core porosity is 1 to 2% lower than conventional analysis porosity. This results from slight compaction that occurs during coring. Medium and low porosity percussion sidewall samples, especially from highly cemented rocks, display porosity that is much too high due to fracturing and grain shattering. The deviation between measured porosity and true porosity becomes greater as the actual porosity decreases. Uncertainty caused by systematic variation in sidewall core porosity relative to plug analysis values can be minimized by development of correlations between sidewall core and conventional core values.<ref name=pt05r38 /> (For more on porosity, see [[Porosity]].)

==[[Permeability]]==

==Permeability==

 

[[file:overview-of-routine-core-analysis_fig3.png|thumb|300px|{{figure number|3}}Data compiled from 5300 sidewall core samples indicate that sidewall cores from low permeability formations have an indicated permeability greater than that determined from conventional core analysis. Sidewall cores from formations with more than 20 md permeability consistently have a measured permeability that is lower than that from conventional analysis. (After <ref name=pt05r38 />; data from <ref name=pt05r82 />.)]]

Whole core samples may contain vugs and fractures that are excluded from core analysis plugs and thus often yield higher permeabilities. To offset this effect, especially in fractured samples, whole core permeability is measured in two horizontal directions. One measurement (reported as ''k'' or ''k''_max) is made parallel to the major fracture planes and reflects the influence of the fractures as flow pathways. The second measurement is made perpendicular to the first. This value, reported as ''k''₉₀, reflects matrix permeability and is close to conventional core analysis permeability.<ref name=pt05r82 />

Whole core samples may contain vugs and fractures that are excluded from core analysis plugs and thus often yield higher permeabilities. To offset this effect, especially in fractured samples, whole core permeability is measured in two horizontal directions. One measurement (reported as ''k'' or ''k''_max) is made parallel to the major fracture planes and reflects the influence of the fractures as flow pathways. The second measurement is made perpendicular to the first. This value, reported as ''k''₉₀, reflects matrix permeability and is close to conventional core analysis permeability.<ref name=pt05r82 />