PETE311_06A_Class04_(Maggard)

PETE311_06A_Class04_(Maggard) - POROSITY DETERMINATION FROM...

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POROSITY DETERMINATION FROM LOGS Most slides in this section are modified primarily from NExT PERF Short Course Notes , 1999. However, many of the NExT slides appears to have been obtained from other primary sources that are not cited. Some slides have a notes section.
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Well Log SP Resistivity OPENHOLE LOG EVALUATION
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Oil sand Gamma ray Resisitivity Porosity Increasing radioactivity Increasing resistivity Increasing porosity Shale Shale POROSITY DETERMINATION BY LOGGING
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POROSITY LOG TYPES 3 Main Log Types • Bulk density • Sonic (acoustic) • Compensated neutron These logs do not measures porosity directly. To accurately calculate porosity, the analyst must know: • Formation lithology • Fluid in pores of sampled reservoir volume
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DENSITY LOGS • Uses radioactive source to generate gamma rays • Gamma ray collides with electrons in formation, losing energy • Detector measures intensity of back- scattered gamma rays, which is related to electron density of the formation • Electron density is a measure of bulk density
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DENSITY LOGS • Bulk density, ρ b , is dependent upon: – Lithology –Poros ity – Density and saturation of fluids in pores • Saturation is fraction of pore volume occupied by a particular fluid (intensive)
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GR API 0 200 CALIX IN 61 6 CALIY IN 6 RHOB G/C3 23 DRHO G/C3 -0.25 0.25 4100 4200 DENSITY LOG Caliper Density correction Gamma ray Density
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Formation ( ρ b ) Long spacing detector Short spacing detector Mud cake ( ρ mc + h mc ) Source
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BULK DENSITY ( ) φ ρ + φ ρ = ρ f ma b 1 Matrix Fluids in flushed zone •Measures electron density of a formation •Strong function of formation bulk density •Matrix bulk density varies with lithology Sandstone 2.65 g/cc Limestone 2.71 g/cc Dolomite 2.87 g/cc
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POROSITY FROM DENSITY LOG Porosity equation ( ) xo h xo mf f S 1 S ρ + ρ = ρ f ma b ma ρ ρ ρ ρ = φ Fluid density equation We usually assume the fluid density ( ρ f ) is between 1.0 and 1.1. If gas is present, the actual ρ f will be < 1.0 and the calculated porosity will be too high. ρ mf is the mud filtrate density, g/cc ρ h is the hydrocarbon density, g/cc S xo is the saturation of the flush/zone, decimal
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DENSITY LOGS Working equation (hydrocarbon zone) ( ) () ma sh sh sh hc xo mf xo b V 1 V S 1 S ρ φ + ρ + ρ φ + ρ φ = ρ ρ b = Recorded parameter (bulk volume) φ S xo ρ mf = Mud filtrate component φ (1 - S xo ) ρ hc = Hydrocarbon component V sh ρ sh = Shale component 1 - φ -V sh = Matrix component
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DENSITY LOGS • If minimal shale, V sh 0 • If ρ hc ≈ρ mf f , then ρ b = φρ f -(1- φ ) ρ ma f ma b ma d ρ ρ ρ ρ = φ = φ φ d = Porosity from density log, fraction ρ ma = Density of formation matrix, g/cm 3 ρ b = Bulk density from log measurement, g/cm 3 ρ f = Density of fluid in rock pores, g/cm 3 ρ hc = Density of hydrocarbons in rock pores, g/cm 3 ρ mf = Density of mud filtrate, g/cm 3 ρ sh = Density of shale, g/cm 3 V sh = Volume of shale, fraction S xo = Mud filtrate saturation in zone invaded by mud filtrate, fraction
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GRC 0 150 SPC MV -160 40 ACAL 61 6 ILDC 0.2 200 SNC 0.2 200 MLLCF 0.2 200 RHOC 1.95 2.95 CNLLC 0.45 -0.15 DT
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This note was uploaded on 12/03/2009 for the course PETE 311 taught by Professor Staff during the Spring '08 term at Texas A&M.

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PETE311_06A_Class04_(Maggard) - POROSITY DETERMINATION FROM...

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