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Scintillators for Geophysical Exploration

Markus Berheide and Brad RoscoeSchlumberger-Doll Research

Cambridge, MA

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Talk Outline

• What does an oil well look like?

• What is the well environment?

• What type of measurements are we interested in

• Performance requirements for scintillators

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Surface Seismic

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Drilling

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Logging While Drilling

(LWD)

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Sample Log

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Open-Hole Logging

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Logging Truck

(Land)

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Open-Hole

Logging Tools

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Cementing

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Perforating

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Cased-Hole Logging

or

Reservoir Monitoring

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Measurement Environment

Max

Temperature (oC)

Shock & Vibration

(g’s)

Tool Diameter (in).

Logging While Drilling 150 - 200 1000’s 4-8 but hole in center

Open-Hole Logging 150 - 200 100’s 3.6 – 4.5

Cased-Hole 150 - 200 100’s 1.7-2.4”

Surface Applications 85 N/A N/A

LWD

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Formation Description

φ1 − φ

Matrix Oil

Water

1=Sw+ So+ Sg

Sw

Gas Sg

So

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Measurement Issues

• Source and sensor both in borehole

• Usually want to measure Formation

• Need to make measurement with 1-3 seconds of data

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What do we want?

• Single Well– Formation Evaluation

• Porosity• Presence of hydrocarbons • Fluid identification• Permeability• Lithology

– Production Monitoring• Oil flow rate• Water flow rate• Gas flow rate

– Misc• Cement integrity• Corrosion• Depth• Etc…

• Reservoir– Size– Orientation– Connectivity– Etc…

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Desirable Scintillator Characteristics(Application Dependent)

• High Density, High Z• Good Resolution (all Energies)• High Countrate Capability• Reasonable Size• Non-Hydroscopic • Light Output (350 – 450 nm)• Rugged• Good High Temperature Performance

– Resolution– Wavelength– Decay Time

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τ

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Scintillators Used in the Industry

• NaI

• BGO

• GSO

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Gamma-Ray Measurement

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γγγγ−−−−γγγγ Density

Formation density

Mudcake density

Mud density

(Mudcake thickness or standoff)

Density radial profile

hmc

Source

BS

SS

LS

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Gamma-Ray Spectroscopy

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RSTHardware

RSTHardware

Schlumberger

NearDetector

Shielding

FarDetector

1-11/16 in RST-A

2-1/2 inRST-B

NeutronGenerator** **

Tool OperationTool Operation

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Sigma Modes

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Inelastic-Capture

Mode

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MethodMethod

Schlumberger

C/O SaturationC/O SaturationC/O Yields MethodC/O Yields Method

1 2 3 4 5 6 7 8Energy [MeV]

Oxygen

Silicon

Calcium

Iron

Carbon

RST-B Far Detector Inelastic Standards

ToolBackground

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Importance of Scintillator Characteristics for

Different Logging Applications

High Temperature

Application High

Density, High Z

Good Resolution

Good Resolution

(High Energy)

High Countrate Capability 350-

450 nm Resolution Decay Time

Stability

Natural Gamma Ray High Medium Low Low High Medium Low

Density Measurement High Medium Low Medium High Medium Medium

Gamma-Ray Spectroscopy High High High High High High High

Sigma Medium Medium Low High High Medium High

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Summary

• Match Scintillator Performance to Application

• Always a Trade-Off

• High Temperature Performance Important– Light output

– Decay time

– Resolution

• Ruggedness and Packaging Important

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Nuclear Well LoggingSchlumberger-Doll Research