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  • Density Log

    POROSITY LOGGING CORE

    LEARNING OBJECTIVES

    By the end of this lesson, you will be able to:

    Describe the logging tool configuration in the borehole and thebasic physics of the Density Log and Litho-Density Logs

    Discuss the units and the scale used for Density log data Explain how Density log data are used to calculate porosity and

    what are the required “inputs”

    Describe the effect of free gas saturation on the bulk density(rb) log and the impact on calculated porosity if 100% liquid isassumed

    Discuss how the correction curve and caliper curve are usedtogether to quality check bulk density log data

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  • POROSITY FROM DENSITY AS SINGLE SENSOR

    Several applications

    Porosity estimation

    Lithology estimation

    Prediction of hydrocarbon density

    Input to synthetic seismograms (density x velocity)

    Formation mechanical properties and rock physics

    TYPICAL DENSITY TOOL CONFIGURATION

    Formation Density Compensated (FDC)

    Density Tool responds to electron density of the formation in front of the tool.

    Density Log response; combination of matrix density and density of fluids in the invaded zone in their relative proportions. For simplicity, we have considered ρw = ρmf.

    Density Log

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  • TYPICAL DENSITY TOOL CONFIGURATION

    The Density Log measures bulk density of formations in open-hole (g/cc).

    In a known lithology, the bulk density is used to determine formation porosity.

    Also an important reference for detecting light hydrocarbons.

    The Density Log has earned its reputation as the most reliable and useful porosity log.

    GAMMA RAY INTERACTIONS

    Cesium 137 Emission

    Limit of GR detection

    PEF

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  • LOGGING TOOLS AVAILABLE

    Wireline Density Measurements LDT = Litho-Density Tool, Schlumberger ZDEN = Litho-Density Tool, Baker Atlas SDLT = Litho-Density Tool, Halliburton MPD = Litho-Density Tool, Weatherford

    LWD Density Measurements ALD = Litho-Density, Sperry (Halliburton) ADN & CDN = Litho-Density, Anadrill (Schlumberger) MDL = Litho-Density, Baker-Huges Inteq AZD = Litho-Density, Weatherford

    DENSITY CORRECTION BY SPINE AND RIBS

    (mm)(6.35) (12.7) (19.05)

    (6.35) (12.7) (19.05)(mm)

    Density Log

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  • LOG OF CORRECTED BULK DENSITY

    (1198.26 kg/m3)

    (0.1524 m) (0.4064 m) .

    VS. CALIPER CURVES

    (0.1524 m) (0.4064 m)

    (454 kg)

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  • VS. CALIPER CURVES

    A. This hole wasdrilled with an8-½ inch (18 mm)drill bit.

    (0.1524 m) (0.4064 m)

    (454 kg)

    VS. CALIPER CURVES

    Good qualitative indication of log quality

    Should be ~ 0 in smooth borehole

    Barite mud exception

    Can be good fractureindicator as well

    (0.1524 m) (0.4064 m)

    (454 kg)

    Density Log

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  • DENSITY TOOL RESPONSE EQUATION

    b = Φ [Sxow + (1-Sxo)h] + (1 - Φ)ma

    b : Formation bulk densityma : Matrix densityf : Fluid densityw : Water densityh : Hydrocarbon densityΦ : Formation porositySxo : Invaded zone water saturation

    Rearrange to calculate porosity, Phi

    Quartz 2.65 g/cc

    Calcite 2.71 g/cc

    Dolomite 2.87 g/cc

    ma b

    ma f

    - = -

    DENSITY VALUES IN FORMATION EVALUATION (G/CC)

    Reservoir matrix

    Quartz (sandstone) 2.65

    Calcite (limestone) 2.71

    Dolomite 2.87

    Pore fluids

    Fresh water 1.00

    Salt water (200 g/l (200 kg/m3)) 1.13

    Fresh water with 30% residual oil 0.90 – 0.94

    Fresh water with 30% residual gas 0.73 – 0.74

    Other minerals

    Halite (rock salt) 2.03

    Anhydrite 2.98

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  • CORE POROSITY CALIBRATION

    Cor

    e po

    rosi

    ty (%

    bv)

    Log density (g/cc)

    Apparent fluid

    Densityfl

    Core matrix density

    ma

    DENSITY LOG RESPONSE CHART

    Porosity = 25%

    Density Log

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  • Remember:Sand (quartz rich)Limestone (calcite rich)

    PEF (OR PE) CURVE

    “Essentially” porosity independent

    Typical values• Sand = 1.8• Limestone = 5.1• Dolomite = 3.1• Salt = 4.7• Anhydrite = 5.1

    Original density log was developed in the 1960s

    Measured bulk density

    Called Formation DensityCompensated Log (FDC)

    Photoelectric Factor Curve(PEF) was later developed

    Density log was renamed Litho-Density Tool (LDT)

    Single curve lithologyindicator

    LITHO-DENSITY TOOLS: PEF (OR PE) CURVE

    Photoelectric Factor (PEF) Incident low energy gamma ray absorbed by electron and

    electron ejected from the atom PEF = (Z/A)exp 3.6 Where: Z = atomic no.

    A = atomic weight

    Measures different part of decay spectrum

    Can be highly affected by barite muds

    Single curve lithology indicator

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  • PE VS. POROSITY: LITHO-DENSITY TOOLS

    Chart Use:

    Read PEF

    Read Bulk Density

    Determine Porosity %

    Porosity = 20%

    SUMMARY: DENSITY AS SINGLE SENSOR

    Source for porosity and lithology information

    Litho-density (PEF) provides additional lithology information

    Pad contact tool Rugose hole implications Barite mud implications Fracture identification implications

    Can be combined with other porosity devices to define lithology,porosity, shale content

    Depth of investigation shallow (< 50 cms)

    Vertical resolution ~ 20 cms

    Density Log

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  • LEARNING OBJECTIVES

    Describe the logging tool configuration in the borehole and thebasic physics of the Density Log and Litho-Density Logs

    Discuss the units and the scale used for Density log data Explain how Density log data are used to calculate porosity and

    what are the required “inputs”

    Describe the effect of free gas saturation on the bulk density (rb)log and the impact on the calculated porosity if 100% liquid isassumed

    Discuss how the correction curve and caliper curve are usedtogether to quality check bulk density log data

    ═════════════════════════════════════════════════════════════════════════Porosity Logging Core

    © PetroSkills, LLC., 2016. All rights reserved._____________________________________________________________________________________________

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