TTP Neutron NT Rev3

7/24/2019 TTP Neutron NT Rev3

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Internal Use Only

Dual Spaced Neutron Tool

(DSNT)



Internal Use Only

Learning Objectives• Understand and identify the applications of the dual spaced neutron tool

• Understand and explain the basic physics involved in the measurements of the dual spaced

neutron tool

• Understand the theory of neutron emitters and neutron detectors

• Identify the units of measurement used for the dual spaced neutron tool and explain how each

is determined

• Identify the depth of investigation and vertical resolution of the DSNT

• Identify the wellbore environments the DSNT will function properly in

• Understand the wellbore parameters which interfere with DSNT quality (require corrections)• Understand the DSNT response versus borehole and formation environment

• Understand the relationship between SS/LS count ratio to lithology and porosity

• Understand the difference between the effect of gas versus the effect of incorrect matrix value

• Identify the master calibration standard, the transfer standard for shop calibrations, and what is

utilized for field calibrations• Understand the difference between slowing down cross section and capture cross section and

their effect on neutron count rates



Internal Use Only

Dual Spaced Neutron – overview

• Applications – Measure porosity

– Help identify lithology (together with the SDLT)

– Indicate Gas (together with the SDLT)

– Quantify shale volume

• Technique

– Neutron bombardment; resulting Neutrons scattered by the

formation & counted at detectors



Internal Use Only

• Output – Neutron porosity ( n) – %

• Design – Am241Be 18.5 Curie (4.6MeV)

– Depth of investigation 6” – Vertical resolution 24”

– Correction charts

• Operating environment

– WBM – OBM

– Cased hole

Dual Spaced Neutron – overview



Internal Use Only

• Emitted Neutrons travel through theformation & collide with nuclei ofatoms in the bulk material

• Neutrons are scattered & lose some

energy• Some Neutrons may lose enough

energy to be absorbed

Dual Spaced Neutron – physics



Internal Use Only

• Dual helium-3

gas

proportional

detectors



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• Thermal neutron (<0.1 eV) population –material dependent – Slowing down cross-section (elastic

scattering cross-section)

– Absorption or capture cross-section



Element Slowing Down X-sectionCollisions to Reach

0.025 eV (thermal)

HydrogenBoron

Carbon

Nitrogen

Oxygen

Sodium

Magnesium

Aluminum

Silicon

Chlorine

Potassium

Calcium

Iron

Cadmium

20.03.0

4.8

10.0

4.1

3.5

3.6

1.5

1.7

10.0

1.5

9.5

11.0

5.3

18105

115

130

150

215

227

251

261

329

362

371

514

1028



ElementThermal Neutron

Capture Cross Section

Hydrogen

Boron

Carbon

Nitrogen

Oxygen

Sodium

Magnesium

Aluminum

Silicon

Chlorine

Potassium

Calcium

IronCadmium

0.33

758.86

0.0035

0.075

0.0002

0.4

0.0625

0.232

0.1638

33.338

2.152

0.455

2.5147000.0




• Hydrogen – High scattering cross-section

– Present in formation fluids

– Function of porosity

– Also present in rock minerals… C, O, Na,Mg, Al, Si, K, Ca, Fe



• Varying porosity





• Varying lithology

Zero Porosity Formations



• DSNT has dual detectors – why?

• Porosity is a function of Calibrated Ratio –

SS/LS

• Porosity is related to count rate through…

Ф = a0 + a1Rc + a2Rc2 + a3Rc

3 …+ anRcn





• Count rate is a function of

– Borehole salinity, size, temperature – Pressure

– Detector stand-off

– Mud weight

– Mudcake thickness




• Standoff – Any separation between formation and detector

– Minimized with a bowspring decentralizer



Dual Spaced Neutron – calibration

• University of Houston

• The logging company

designates a standard tool

to measure count rates

• Fresh water filled formations




Calibration forces the tool tomeasure the same ratio as the

standard tool in the HWT

Transfer standard

Calibration ensures Accurate values of Φ

All* neutron tools measure

the same response in the

same formation and under

the same borehole conditions

* both internal and

competitors!




SS/LS Ratio determined at theshop

Serves as a wellsite

verification

Ensures tool response is thesame before and after logging



R i


http://slidepdf.com/reader/full/ttp-neutron-nt-rev3 20/20I t l U O l

Review• Understand and identify the applications of the dual spaced neutron tool

• Understand and explain the basic physics involved in the measurements of the dual spaced

neutron tool

• Understand the theory of neutron emitters and neutron detectors• Identify the units of measurement used for the dual spaced neutron tool and explain how each

is determined

• Identify the depth of investigation and vertical resolution of the DSNT

• Identify the wellbore environments the DSNT will function properly in

• Understand the wellbore parameters which interfere with DSNT quality (require corrections)• Understand the DSNT response versus borehole and formation environment

• Understand the relationship between SS/LS count ratio to lithology and porosity

• Understand the difference between the effect of gas versus the effect of incorrect matrix value

• Identify the master calibration standard, the transfer standard for shop calibrations, and what is

utilized for field calibrations• Understand the difference between slowing down cross section and capture cross section and

their effect on neutron count rates

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TTP Neutron NT Rev3

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