Neutrons as a multifunctional tool for geophysicists

Transcription

1 Neutrons as a multifunctional tool for geophysicists Urszula Woźnicka Tomasz Zorski H. Niewodniczanski Institute AGH University of Science of Nuclear Physics, PAN and Technology Kraków, Poland Kraków, Poland 3rd Workshop on Neutron Measurements, Evaluations and Applications October 25-28, 2006, Borovets, Bulgaria

2 The Henryk Niewodniczanski Institute of Nuclear Physics IFJ PAN Kraków, Poland AGH University of Science and Technology Dept. of Geophysics Kraków,, Poland Our experience and achievement in nuclear geophysics

3 Professor Jan A. Czubek nuclear geophysicist Close cooperation: : IFJ & AGH NUCLEAR GEOPHYSICS Theoretical research Field and laboratory measurements Monte Carlo simulations Semi-empirical calibration method for neutron tools Sigma-a laboratory measurement method FLUKA, MCNP

4 Speach outline Borehole Borehole tools, tools, Measurements, Measurements, Comprehensive Comprehensive interpretation interpretation Spectrometric Spectrometric Neutron-Gamma Neutron-Gamma Logging LoggingTool Neutron-Neutron Neutron-Neutron Logging LoggingTool Neutron Neutron Lifetime Lifetime Logging LoggingTool Σ a a Complex Nuclear Tool CxNT

5 Borehole geophysics Well logs Electric Acoustic Nuclear Measured values Resistivity istivity,, LLD, LLS Transit interval time, DT Bulk density, RHOB ( ) + Laboratory analysis of the core sonde borehole rock Neutron porosity, NPHI Natural radioactivity, GR ( )

6 Comprehensive interpretation of well logs Input data: measurements (logs) in the borehole along the depth Output results: lithology, porosity, saturation fluids of the rock

7 Comprehensive interpretation of well logs For example: natural gamma measurement Pore space Clay minerals Sand- stone Other minerals γ = φs w γ w + V cl γ cl + V sand γ sand + V lim γ lim + V k min k γ min k Nat. γ detector

8 Spectrometric Neutron-Gamma Logging Tool Measurement method Tool calibration - Calibration Facility - Monte Carlo simulations (library problems)

9 Spectrometric Neutron-Gamma Log SNG BGO A A+ 1 A+ 1 Z X + n ZX ZX + * γ Neutron source γ from radiative capture A Z X Slown down neutron Counts rate [pulse/600 s] H (1,71-2,35 MeV) H: 2,223 MeV Si:3,539 MeV Si:4,934 MeV Si (2,67-5,03MeV) Ca (5,25-6,64MeV) Sandstone Piaskowiec Radków Limestone Wapień Józefów Sandstone Piaskowiec Mucharz Fe: 7,631MeV 7,646 MeV Fe (6,85-10MeV) Ca: 6,418MeV Number of channel

10 Calibration of the Neutron-Gamma Tool Measurement in calibration blocks of known concentration of H, Si, Ca, Fe Multiple linear regression Element Eγ [MeV] Window ΔEγ H Si 3.54, Ca Fe 7.631, C el chem = b el 0 i + = i= 4 1 el i b i I eli pom el : H, Si, Ca, Fe concentration gamma counts

11 Calibration Facility in the Well Logging Base Zielona Góra, Poland General view of Calibration Facility site during calibration measurements. The wood board covers two big pools where all calibration blocks are stored. The pool contains 18 natural rocks standards for basic neutron tool calibration (4 limestones, 4 sandstones and 1 dolomite - each of them for two hole diameters). Proprietor: Geofizyka Kraków Company & AGH University

12 Calibration Facility in the Well Logging Base Experimental Tool Calibration: Basic neutron porosity/lithology calibration, Natural gamma calibration (API, K, U, Th), Vertical response tool analysis. Artificial rock models for a determination of the Vertical Response Function for nuclear tools. The models are constructed of the specially prepared ceramic bricks and consist of the set of thick and thin layers. The dimension of the single brick is 30 x 30 x 7.5 cm. Three porosities: 16, 25 and 60% are available for these models. The models are located inside the 3 m deep concrete pool filled always by water. These models were constructed by the AGH University.

13 Monte Carlo Calibration of the Neutron-Gamma Tool Modeling of the the spectrometric neutron-gamma well logging probe, SO SN Aluminium Water pool Rock model n-gamma probe (SO-5-90-SN type) Detector (BGO) Steel Lead Am-Be soure BGO detector Hole Am-Be source Concrete base

14 Calibration of the Neutron-Gamma Tool 5 4 C-Fe-MCNP [wt.%] 3 2 R 2 = (9 punktów) Mu2 Br2 R 2 = (21 punktów) 1 0 Ra2 Ze2 BM2 Pi2 Jo2 Mo2 Li2 95% p.ufności C-Fe-chem [wt.%] Experimental calibration points Numerical calibration points

15 Cl(n,γ)Cl - gamma ray lines endf60 Cl(n,γ)Cl - gamma ray lines Eγ (MeV) Iγ (per 100 captures) Iγ (per 100 captures) Monte Carlo Calibration of the Neutron-Gamma Tool Problems with the ENDF libraries ACTIA Eγ (MeV)

16 Monte Carlo Calibration of the Neutron-Gamma Tool Problems with the ENDF libraries Al(n,γ )Al gam m a-ray lines Iγ (per 100 captures) M ev (delayed) ACTIA E γ (MeV)

17 Neutron-Neutron Logging Tool Neutron field in rock medium Calibration of the n n tool - Semi-empirical empirical method - Monte-Carlo simulation Thermal neutron absorption cross section - Laboratory measurement - Borehole neutron generator - NNTE - tool

18 Neutron-Neutron Tool Neutron detectors Neutron source e.g. AmBe Isolines of the neutron field

19 Neutron-Neutron Tool: Detector response Homogenous infinite medium: φ th ( r) = similarly: Q 4πΣ I th Borehole geometry: a = L 2 s f P L 2 d e ( L, Σ,P) m r / a L s e r r / L d L m Detector Neutron source I th = f ( L, Σ, P ) map ap ap L map Detektor = f ( GNP) L m General Neutron Parameter Źródło neutronowe

20 Calibration of the Neutron-Neutron Tool Neutron measurement Tool response GNP: General Neutron Parameter - slowing down length - diffusion length - absorption cross section (i.e.:.: integral neutron parameters) Geological parameter Porosity A B C A, B, C - Borehole diameter

21 Calibration of the Neutron-Neutron Tool Procedures Real measurements Calibration Facility Simulation measurements Monte Carlo Nuclear tool NNTE loggingl water Water block Standard rock concrete Concrete necessarily not necessarily Analytical solutions of the neutron transport phenomena in a borehole geometry

22 Calibration of the Neutron-Neutron Tool The important parameter of the rock medium indispensable for the geological interpretation of the neutron neutron tool: Thermal neutron absorption cross section of the rock matrix Σ a Laboratory measurent on on core core samples in in situ: situ: Neutron Lifetime Log Log in in situ: situ: Improved neutron-neutron tool tool NNTE

23 Calibration of the Neutron-Neutron Tool Σ a Laboratory measurement Rock sample Moderator Cadmium surrounding

24 Calibration of the Neutron-Neutron Tool using a pulsed neutron generator (Czubek s method)

25 Calibration of the Neutron-Neutron Tool Neutron lifetine logging: borehole pulsed neutron generator source:

26 Neutron-neutron neutron thermal-epithermal epithermal well logging tool NNTE Near epithermal detector źródło Am-Be Far epithermal detector Near thermal detector Prototype: AGH University and Geofizyka Kraków Company

27 Idea of the Complex Nuclear Tool CxNT During last three years we made field measurements using the NNTE, SNG and SNA methods, working as the separate experimental tools. These works confirmed that expected valuable geological information can be retrieved from this kind of measurement. It became clear that the new complex tool must be made because of the optimisation of the time service. Thin bedded, shaly sand gas formation in Carpathian Foredeep, Poland was place of experiments.

28 Cable (7 wires, 5000 m) Digital data transmission block (at least 25 channels) K, U, Th Spectral Gamma-Ray Log SGR (BGO, MeV) Σ a, porosity Σ a, porosity NNTE 3 He Far detectors (thermal/epithermal) 3 He Near detectors (thermal/epithermal) AmBe neutron source (6 18 Ci) Si, Ca, Fe Cl, S Al Spectral Neutron-Gamma SNG (BGO, MeV) Neutron Activation SNA (BGO, MeV)

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30 Comprehensive interpretation of well logs POROSITY (WATER, HYDROCARBONS) QUARTZ DEPTH [m] LIMESTONE CLAY

31 Comprehensive interpretation of well logs Each log is described by the equation which joint porosity, saturation and various mineralogical components with the tool response: Measured signal of the i-th tool n ( a V ) i = 1 m MLi = ij j,..., j= 1 Solution of the set of equations ML i : Volume fraction of the j-th component V j : Φ porosity S saturation (water, hydrocarbons ) V m mineral components (rock marix, clay )