Changes

===Spatial resolution===

===Spatial resolution===

The spatial resolution of core information must be considered relative to that of the formation itself and to the vertical resolution and depth of investigation of the logging responses to be used in the analysis. Core has physical dimensions that can be discretely measured. Should the formation possess attributes that exceed these dimensions, precise prediction of those attributes cannot be expected. An example would be porosity obtained from 1-in-diameter core plugs taken from a conglomeratic reservoir, where the clast size can exceed [[length::6 in.]] or more. Any attempt to determine an average porosity from conventional core analysis would need to consider the sampling problem. In this case, it may be more appropriate to use information contained in the log responses for obtaining a true measure of porosity.

The spatial resolution of core information must be considered relative to that of the formation itself and to the vertical resolution and depth of investigation of the logging responses to be used in the analysis. Core has physical dimensions that can be discretely measured. Should the formation possess attributes that exceed these dimensions, precise prediction of those attributes cannot be expected. An example would be [[porosity]] obtained from 1-in-diameter core plugs taken from a conglomeratic reservoir, where the clast size can exceed [[length::6 in.]] or more. Any attempt to determine an average porosity from conventional core analysis would need to consider the sampling problem. In this case, it may be more appropriate to use information contained in the log responses for obtaining a true measure of porosity.

If one considers the zone of investigation of the formation density tool in an 8-in. borehole ([[:file:core-log-transformations-and-porosity-permeability-relationships_fig3.png|Figure 3]]), the volume of rock ''seen'' by the tool encompasses roughly one quadrant, with a nominal penetration depth of [[length::4 in.]] and a thickness of [[length::24 in.]] This equates to more than 900 in.³ of material measured. When this is compared to a 1-in. core plug [[length::3 in.]] long, the log measures almost 400 times the volume measured by the plug.

If one considers the zone of investigation of the formation density tool in an 8-in. borehole ([[:file:core-log-transformations-and-porosity-permeability-relationships_fig3.png|Figure 3]]), the volume of rock ''seen'' by the tool encompasses roughly one quadrant, with a nominal penetration depth of [[length::4 in.]] and a thickness of [[length::24 in.]] This equates to more than 900 in.³ of material measured. When this is compared to a 1-in. core plug [[length::3 in.]] long, the log measures almost 400 times the volume measured by the plug.