Changes

[[file:difficult-lithologies_fig2.png|thumb|300px|{{figure number|2}}UMAA determination chart. © Schlumberger Educational Services, 1989.]]

[[file:difficult-lithologies_fig2.png|thumb|300px|{{figure number|2}}UMAA determination chart. © Schlumberger Educational Services, 1989.]]

The MID or ''m''atrix ''id''entification crossplot uses the apparent volumetric cross section (UMAA) and the apparent matrix grain density (RHOMAA) to identify minerals. UMAA represents the projection of the volumetric photoelectric absorption index, U (the product of Pe and electronic density), to the value at zero porosity. RHOMAA results from a mathematical projection of the bulk density of an interval to its value at zero porosity. These projections to zero porosity effectively eliminate variance due to porosity, resulting in a variance mainly due to lithology.

The MID or ''m''atrix ''id''entification crossplot uses the apparent volumetric [[cross section]] (UMAA) and the apparent matrix grain density (RHOMAA) to identify minerals. UMAA represents the projection of the volumetric photoelectric absorption index, U (the product of Pe and electronic density), to the value at zero porosity. RHOMAA results from a mathematical projection of the bulk density of an interval to its value at zero porosity. These projections to zero porosity effectively eliminate variance due to porosity, resulting in a variance mainly due to lithology.

This method requires that an estimate of total porosity be determined first. Typically, this can be done from a density-neutron crossplot (see [[Standard interpretation]]). Using this porosity, an apparent matrix density is determined from the following equation:

This method requires that an estimate of total porosity be determined first. Typically, this can be done from a density-neutron crossplot (see [[Standard interpretation]]). Using this porosity, an apparent matrix density is determined from the following equation: