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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 andwhat 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 density
ma : Matrix density
f : Fluid density
w : Water density
h : Hydrocarbon densityΦ : Formation porosity
Sxo : 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
Co
re p
oro
sity
(%
bv)
Log density (g/cc)
Apparent fluid
Density
fl
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 andwhat 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._____________________________________________________________________________________________
11
COPYRIGHT