1. 1. 1
2. 2. Presentation on Neutron Log2Zubair Kamboh
3. 3. Contents3 Log Neutron log Hydrogen Index Tools Log format Log Presentation Calibration Log characteristics Applications The Neutron-Density Combination Conclusion References
4. 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. 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. 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. 7. 7The slowing of fast neutrons with time by elastic collision withformation nuclei (After Dr. Paul Glover.)
8. 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. 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. 10. 10TOOLS
11. 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. 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. 13. LogPresentation13
14. 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. 15. 15Graph for deriving the true porosity from Schlumberger CNL tool values fordefined sandstone, limestone, and dolomite matrices (fromSchlumberger,1972)
16. 16. Log characteristicsDepth of Investigation:15-25 cmVaries with HI and therefore porosityVertical Resolution:60cm with SNP40cm with CNL16
17. 17. ApplicationsQuantitativeQualitative17
18. 18. QUANTITAVE USEPorosity calculation:Log10=N+Bwhere= porosity, B= constantsN=neutron tool reading18
19. 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. 20. The Hydrocarbon gas effect in the neutron log. (CNLSchlumberger, M H Rider, 1986,.)20
21. 21. QUANTITAVE USEThe Shale Effect on neutron porosity:Increases the hydrogen index of the formationOverestimation of Neutron porosity due to boundwater21
22. 22. QUALITATIVE USELithology identification:ShaleSandEvaporitesCoalVolcanic and Intrusive rock22
23. 23. The neutron logshows porosities ofdifferent lithologies.(after Rider, 1986).23
24. 24. The neutron logresponse tomixtures of shalesand sandstones.(After Dr. PaulGlover.)24
25. 25. Neutron log responseto evaporites (afterRider, 1997).25
26. 26. The Neutron-DensityCombinationClean FormationsNo separation for pure limestonesSmall negative separation for clean sandstones.Moderate positive separation for pure dolomites26
27. 27. 27The density-neutron cross-plot. (M H Rider,1986,.)
28. 28. 28The density-neutroncombination idealizedresponses.
29. 29. 29Distinctive evaporites on a density-neutron log.(M H Rider,1986,.)
30. 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. 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