USC_Class_Section_7_GR_3pp_ppt

USC_Class_Section_7_GR_3pp_ppt - PTE-461 Formation...

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1 Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 7: Gamma Ray Slide No.: 1 PTE-461 Formation Evaluation Fall Semester, 2007 Section 7 Natural (Passive) Gamma Ray Logs Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 7: Gamma Ray Slide No.: 2 What Do Gamma Ray Logs Measure? • Natural gamma radiation from the materials in and surrounding a borehole • A passive measurement • Natural ± -ray sources are Potassium ( 40 K), Uranium ( 238 U), and Thorium ( 232 Th) • Because clay minerals contain K, ± -ray logs are used (almost exclusively) to estimate shale volumes, in reservoir rocks Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 7: Gamma Ray Slide No.: 3 Background •F i r s t ± -ray logs run by Humble (reported: 1939), using ionization chamber to measure natural radioactivity in well bore • Uranium Boom, following WW-II sparked ± -ray measurements ± -ray emission found to correlate to geology
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2 Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 7: Gamma Ray Slide No.: 4 Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 7: Gamma Ray Slide No.: 5 Detailed K-U-Th Spectra 40 K has only one decay, to 40 Ar 238 U and 232 Th decay series involve many daughter products, with half-lives ranging from seconds to billions of years • Not all decays in 238 U and 232 Th series involve ± -ray emission Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com PTE-461: Fal 2007 Section 7: Gamma Ray Slide No.: 6 Why Run Passive ± -Ray Logs • Shales contain more naturally radioactive minerals than clean, non-arkosic (feldspathic), ion-glauconitic, non- monazite, non-zircon rich sands, limestones, and non-potash evaporites – Shales have high potassium content and collect uranium and thorium salts ± -ray logs often used as shale indicator ± -ray logs can be used for well-to-well correlation (even in cased wells) ± -ray logs used to estimate relative amounts of clay minerals in formations (with assumed petrophysical model) ± -ray logs can be used to provide rough estimates of effective porosity and permeability (with assumed petrophysical model) – This requires a petrophysical model and MUCH faith
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3 Donald G. Hil , Ph.D., R.Gp, R. G., R.P.G., L.P.Gp. Dgh@hil petro.com
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This note was uploaded on 02/27/2008 for the course PTE 461 taught by Professor Donhill during the Fall '07 term at USC.

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USC_Class_Section_7_GR_3pp_ppt - PTE-461 Formation...

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