3. Contents3 Log Neutron log Hydrogen Index Tools Log format
Log Presentation Calibration Log characteristics Applications The
Neutron-Density Combination Conclusion References
4. LOGContinuous record as function of depth Of observationmade
on the rock and fluids of the geological sectionexposed in a well
bore.Graphically plotted to scale on narrow paper strip4
5. Neutron LogA reaction between radioactive elements emits
fastneutrons, which collide with the nuclei of otheratoms, most
importantly hydrogen nuclei. Detectorscount the slowed neutrons
deflected back to the tool. Anapparent neutron porosity can be
obtained based on thehydrogen index.5
6. 6The fast neutron slowing efficiency of hydrogen, silicon
and oxygen atomsas a function of neutron energy for a clean
sandstone, = 0.15 (After Dr.Paul Glover.)
7. 7The slowing of fast neutrons with time by elastic collision
withformation nuclei (After Dr. Paul Glover.)
8. Hydrogen IndexHydrogen Index of a material is defined as the
partialconcentration of hydrogen per unit volume relative
towater.It is an indication of richness of hydrogen in
theformation.8
9. ToolsThere are three main types of neutron tool, which
are:The Gamma Ray/Neutron Tool (GNT)The Sidewall Neutron Porosity
Tool (SNP)The Compensated Neutron Log (CNL)9
10. 10TOOLS
11. Log FormatScale is arithmeticPlotted across Track 2 and
3Scale is 45(left)-15 Porosity UnitsShowed in Dashed LineGenerally
combined with density, caliper and gammaray tools11
12. Log PresentationThe scale at the top of the log shows
(negative) -15%porosity on the right, 0% about 1/4 of the way over,
and45% porosity on the left. Sandstones have an absolutemaximum of
about 28% porosity. Shale porosity ismuch higher, but because the
grain size of shale is sosmall, oil or gas trapped in shale cannot
usually beremoved by drilling for it, so shale porosity is
generallynot important.12
13. LogPresentation13
14. CalibrationAPI Neutron Calibration Pit at the University of
HoustonThree blocks of carbonate with accurately knownporosities
that are filled with fresh water.19% porosity Indiana limestone,
API value of 1000 APIneutron units.The response of the tool is then
checked in 1.9%Carthage Marble, 26 % Austin limestone, and
100%fresh water.14
15. 15Graph for deriving the true porosity from Schlumberger
CNL tool values fordefined sandstone, limestone, and dolomite
matrices (fromSchlumberger,1972)
16. Log characteristicsDepth of Investigation:15-25 cmVaries
with HI and therefore porosityVertical Resolution:60cm with SNP40cm
with CNL16
19. QUANTITAVE USEHydrocarbon effects on neutron
porosity:Liquid hydrocarbon (oil) does not affect the
toolresponseHydrocarbon gas has a much lower hydrocarbonindex
resulting from its low density, hence gives rise tounderestimations
of neutron porosity19
20. The Hydrocarbon gas effect in the neutron log.
(CNLSchlumberger, M H Rider, 1986,.)20
21. QUANTITAVE USEThe Shale Effect on neutron
porosity:Increases the hydrogen index of the
formationOverestimation of Neutron porosity due to
boundwater21
22. QUALITATIVE USELithology
identification:ShaleSandEvaporitesCoalVolcanic and Intrusive
rock22
23. The neutron logshows porosities ofdifferent
lithologies.(after Rider, 1986).23
24. The neutron logresponse tomixtures of shalesand
sandstones.(After Dr. PaulGlover.)24
26. The Neutron-DensityCombinationClean FormationsNo separation
for pure limestonesSmall negative separation for clean
sandstones.Moderate positive separation for pure dolomites26
27. 27The density-neutron cross-plot. (M H Rider,1986,.)
29. 29Distinctive evaporites on a density-neutron log.(M H
Rider,1986,.)
30. ConclusionThe neutron-density combination is best
lithologyindicator for most formationsShales and shaliness and
evaporites can be identifiedClean formations and even matrix type
can besuggested30
31. ReferencesEngler.T.W.(2011). Neutron Logs-Lecture Notes
ForPET.370.Glover. P. The Neutron Log- Petrophysicist MSc
CourseNotes .pp.152-171.Rider.M.H. (1986, 1987).The
GeochemicalInterpretation Of Well
Logs.pp.106-118.Serra.O.(1984).Fundamentals of
well-logInterpretation.p.135.http://ipims.com/data/fe11/G4426.asp?UserID=&Code=3002531