Chapter 15. pdf

15.11.4
Distinctive Lithologies
Certain minerals have unusual combinations
of density and neutron porosity. These
unusual combinations can be used to identify
them on a combination log. Examples are
given in Fig. 15.16.
Coals are a good example of a distinctive
combination of density and neutron porosity
values. They have unusually low densities
combined with unusually high apparent
neutron porosity values associated with their
hydrogen content.
15.11.5
 
Evaporites
Remember from the section about the
formation density tool that evaporites can
often be recognized because their often pure
nature leads to well constrained density
values. Evaporites have apparent neutron
porosity values which are either very high or
very low. The combination of well
constrained density values and very high or
very low apparent neutron porosity values is
a characteristic and diagnostic combination
for evaporites (Fig. 15.17).
Fig 15.16
Distinctive minerals on a density-neutron log.
sand
sh
sand
log
sh
V
Ω
−
Ω
Ω
−
Ω
=

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Petrophysics MSc Course Notes The Neutron Log
Dr. Paul Glover Page 171
Fig 15.17
Distinctive evaporites on a density-neutron log.

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Document Outline

• 15.1 Introduction
• 15.2 Theory
• 15.2.1 Neutron Emission
• 15.2.2 Neutron Scattering
• 15.2.3 Neutron Absorption
• 15.2.4 Hydrogen Index
• 15.3 Tool Operation
• 15.3.1 Gamma Ray/Neutron Tool (GNT)
• 15.3.2 Sidewall Neutron Porosity Tool (SNP)
• 15.3.3 Compensated Neutron Log (CNL)
• 15.4 Log Presentation
• 15.5 Calibration
• 15.5.1 The GNT Tool
• 15.5.2 The SNP and CNL Tools
• 15.6 Depth of Investigation
• 15.7 Vertical Resolution
• 15.8 Borehole Quality
• 15.9 Mud Type
• 15.10 Uses of the Neutron Log
• 15.10.1 Determination of Porosity
• 15.10.2 Determination of Lithology
• 15.11 Lithological Identification using the Neutron-Density Combination
• 15.11.1 Compatible Scales and the Density-Neutron Cross-plot
• 15.11.2 Clean Formations
• 15.11.3 Shaly Formations
• 15.11.4 Distinctive Lithologies
• 15.11.5 Evaporites