Neutron log

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Neutron log

  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. LOGContinuous 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 LogA 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, ø = 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 IndexHydrogen 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 FormatScale is arithmeticPlotted across Track 2 and 3Scale is 45(left)-15 Porosity UnitsShowed in Dashed LineGenerally 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 HoustonThree 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 cmVaries with HI and therefore porosityVertical Resolution:60cm with SNP40cm with CNL16
  17. 17. ApplicationsQuantitativeQualitative17
  18. 18. QUANTITAVE USEPorosity calculation:Log10ø=αN+BwhereØ= porosityα, B= constantsN=neutron tool reading18
  19. 19. QUANTITAVE USEHydrocarbon effects on neutron porosity:Liquid hydrocarbon (oil) does not affect the toolresponseHydrocarbon 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 formationOverestimation of Neutron porosity due to boundwater21
  22. 22. QUALITATIVE USELithology identification:ShaleSandEvaporitesCoalVolcanic 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 FormationsNo separation for pure limestonesSmall 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. ConclusionThe neutron-density combination is best lithologyindicator for most formationsShales and shaliness and evaporites can be identifiedClean 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

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