Can accelerator-based radiation sources replace the chemical

Report
Richard Odom
O-GeoSolutions
CAARI 2010
Theme: Radiation-based measurements are an
important tool in oilfield development, but it
would be desirable to use accelerators rather
than Radio-isotope sources.
 Security,
terrorism and RDD’s
 Stewardship
 Personnel
and liability
Safety and Exposure
Predominate Applications:
Formation Density
Source: 2Ci Cesium
Neutron porosity
Source: 20Ci AmBe
From Ellis
Logging background: N-D synergy
Water-filled limestone
Water-filled sandstone
Water-filled Shale
Gas-filled sandstone
Logging background: NeutronDensity plus resistivity
Neutron Generator (enabled)
Measurements
 Thermal
Neutron Lifetime (Sigma)
 Inelastic
gamma spectroscopy for
Carbon and Oxygen
 Prompt-neutron
 Cased-hole
logging for U235
pulsed-neutron density
Accelerator Time line







1960’s Lab development of neutron generators
1970’s commercialization Pulsed-neutron
1980’s commercialization of neutron-induced
spectroscopy systems (Carbon/Oxygen)
1980’s development and field trials of LINAC
density tool by Schlumberger
1990’s accelerator-based Neutron Porosity
1990’s Cased-hole pulsed-neutron density
1990’s development of LWD pulsed-neutron
density
So what will it take to replace the
radio-isotope sources?

Equivalent measurements within environment and
economic constraints

Existing Neutron-Density are simple systems!

Existing analysis paradigms have deep roots

Neutron porosity is easier than density

Impetus
 Value added
 Regulatory
Marketing Study of LWD features
#4
Desirable
Feature
A New Integrated LWD Platform Brings Next-Generation Formation
Evaluation Services, Weller et al. SPWLA 2005
Value added
Neutron generator replaces AmBe
source for neutron porosity.
 Neutron generator and gamma
detectors for pulsed-neutron density


But, in the end, focused density image
was needed. The Cesium source is still
used for imaging and density.
Example: Cased-hole PN density
Gamma Rays are
Compton scattered in
transit to a long-spaced
detector
Gamma Rays are
created from inelastic
scattering proximal to
the neutron generator
Two formations with same density,
but different Hydrogen content
Improvements in a through-casing pulsed-neutron density log,
Odom et al. 2001, SPE 71742
Inverse
methods
Deterministic
model for two
gamma
detectors and a
fast-neutron
detector
2-Group
diffusion theory
model
Inverse
methods
Empirical Methods
Inputs:
Pulsed-neutron
measurements
Outputs:
Density Porosity
Neutron Porosity
Value-added: Deeper penetration
allows density measurement in casedwellbores

Typical correlation:
~3 p.u.

Cased-hole Uncertainty
 Hole-size
 Cement quality
 eccentricity

Where’s the value?
 Moving the rig
 Lowered liability
 Open-hole accuracy
So what will it take to replace the
radio-isotope sources?

Equivalent measurements within environment and
economic constraints

Existing Neutron-Density are simple systems!

Existing analysis paradigms have deep roots

Neutron porosity is easier than density

Impetus
 Value added
 Regulatory
Constraints: Power Consumption
These systems operate on very long
extension cords or batteries
 Optimal:
15 watts
 Useable:
30 watts
 Borderline:
100 watts
 No
Bueno: >200 watts
Constraints: Size
Constrained by wellbore size and use in
logging stack
 Optimal:
1.75-inch O.D., 15-foot length
 Useable:
2.75-inch O.D., 20-foot length
 Borderline:
4-inch O.D., 25-foot length
 No
Bueno: >5-inch O.D., >30-foot length
Constraints: Operating Temperature
Wells are Hot!
 Optimal:
175 C
 Useable:
150 C
 Borderline:
125 C
 No
Bueno: < 100 C
Constraints: MTBF or servicing
Ask BP, Failure is not an option
 Optimal:
2000 operating hours
 Useable:
500 operating hours
 Borderline:
200 operating hours
 No
<100 operating hours
Bueno:
Constraints: Sample Time
Time is Money!
 Optimal:
4 seconds
 Useable:
8 seconds
 Borderline:
16 seconds
 No
Bueno: < 20 seconds
Constraints: System Cost
Typical cost Neutron-Density with sources: $150K
 Optimal:
$150K
 Useable:
$200K
 Borderline:
$250K
 No
>$300K
Bueno:
Conclusions: Can it be done?

Technical
 There are systems and techniques that could
supplant need for radio-isotope logging
Regulatory: it’s a Wild-Card
 Finding Added Value? Research!!


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

More radiation per watt
Improved ion sources
Improved targets
High voltage efficiency
Rugged and Tough solutions
Next generation Algorithms and Models
Thank You!

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