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!! More radiation per watt Improved ion sources Improved targets High voltage efficiency Rugged and Tough solutions Next generation Algorithms and Models Thank You!