CAN ACCELERATOR-BASED RADIATION SOURCES REPLACE

THE CHEMICAL-BASED SOURCES COMMONLY USED IN GEOPHYSICAL EXPLORATION?

Richard OdomO-GeoSolutionsCAARI 2010

Theme:

Security, terrorism and RDD’s

Stewardship and liability

Personnel Safety and Exposure

Radiation-based measurements are an important tool in oilfield development, but it would be desirable to use accelerators rather than Radio-isotope sources.

WELL LOGGING WITH RADIO-ISOTOPES

Predominate Applications: Formation Density Neutron porosity

Source: 2Ci Cesium Source: 20Ci AmBeFrom Ellis

Logging background: N-D synergy

Water-filled limestone

Water-filled sandstone

Water-filled Shale

Gas-filled sandstone

Logging background: Neutron-Density plus resistivity

Neutron Generator (enabled) Measurements

Thermal Neutron Lifetime (Sigma) Inelastic gamma spectroscopy for

Carbon and Oxygen

Prompt-neutron logging for U235

Cased-hole 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

ImpetusValue added

Regulatory

Marketing Study of LWD features

#4DesirableFeature

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 created from inelastic scattering proximal to the neutron generator

Gamma Rays are Compton scattered in transit to a long-spaced detector

Two formations with same density, but different Hydrogen content

Target

Detector

Improvements in a through-casing pulsed-neutron density log, Odom et al. 2001, SPE 71742

Inverse methods

2-Group diffusion theory model

Deterministic model for two gamma detectors and a fast-neutron detector

Inverse methods

Inputs:Pulsed-neutron measurements

Outputs:Density Porosity

Neutron Porosity

Empirical Methods

Value-added: Deeper penetration allows density measurement in cased-wellbores

Typical correlation:~3 p.u.

Cased-hole UncertaintyHole-sizeCement qualityeccentricity

Where’s the value?Moving the rigLowered liabilityOpen-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

ImpetusValue added

Regulatory

Constraints: Power Consumption

Optimal: 15 watts

Useable: 30 watts

Borderline: 100 watts

No Bueno: >200 watts

These systems operate on very long extension cords or batteries

Constraints: Size

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

Constrained by wellbore size and use in logging stack

Constraints: Operating Temperature

Optimal: 175 C

Useable: 150 C

Borderline: 125 C

No Bueno: < 100 C

Wells are Hot!

Constraints: MTBF or servicing

Optimal: 2000 operating hours

Useable: 500 operating hours

Borderline: 200 operating hours

No Bueno: <100 operating hours

Ask BP, Failure is not an option

Constraints: Sample Time

Optimal: 4 seconds

Useable: 8 seconds

Borderline: 16 seconds

No Bueno: < 20 seconds

Time is Money!

Constraints: System Cost

Optimal: $150K

Useable: $200K

Borderline: $250K

No Bueno: >$300K

Typical cost Neutron-Density with sources: $150K

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!!

More radiation per wattImproved ion sourcesImproved targetsHigh voltage efficiencyRugged and Tough solutionsNext generation Algorithms and Models

Thank You!