TTP Density NT Rev2

7/24/2019 TTP Density NT Rev2

http://slidepdf.com/reader/full/ttp-density-nt-rev2 1/23

Internal Use Only

Density Theory

(Spectral Density Tool, Fluid Density

Tool)

SDLT



Internal Use Only

Learning Objectives• Understand and identify the applications of the spectral density tool

• Understand and explain the basic physics involved in the measurements of the spectral density

tool including various gamma energies and their corresponding interaction with matter

• Understand the theory of gamma emitting sources, detectors and PM tubes (including voltage

stabilization for temperature), and the use of windows for energy level measurements.

• Identify the output by the spectral density tool and explain how each is determined

• Identify the depth of investigation and vertical resolution of the SDLT

• Identify the wellbore environments the spectral density tool will function properly in

• Understand the wellbore parameters which interfere with spectral density tool quality (requirecorrections)

• Understand the spectral density tool response versus borehole and formation environment

• Identify the matrix density and Pe values for Sandstone, Limestone, Dolomite, Shale

• Understand the parameters and calculate density porosity from a bulk density measurement

• Understand the difference between the effect of gas versus the effect of incorrect matrix densityvalue

• Identify the master calibration standard, the transfer standard for shop calibrations, and what is

utilized for field calibrations



Internal Use Only

Spectral Density – overview

• Applications – Measure density & infer porosity

– Help identify lithology (together with the DSNT)

– Indicate Gas (together with the DSNT)

– Quantify shale volume (some instances)• Technique

– Gamma bombardment; resulting Gamma rays scattered by the

formation & counted at detectors



Internal Use Only

• Output

– Bulk density ( b) – gm/cc

– Density porosity ( D) – %

– Density correction – gm/cc

– photoelectric factor (Pe)

– Caliper – inches




Internal Use Only

• Design

– Cs137 – 1.5Curie (0.662 MeV)

– Depth of investigation ( b) 1.5”, (Pe) 0.5”

– Vertical resolution ( b) 18”, (Pe) 19” – Correction charts

• Operating environment

– WBM – OBM

– Air/Foam drilled




Internal Use Only

• Emitted Gamma rays travel through the

formation & collide with electrons in the bulk

material

• Gamma rays are scattered & lose some

energy (Compton Scattering)

– Primarily collisions with outer shell electrons which are lithology INDEPENDENT

• Ultimately (< 100-keV), some gammas may

lose enough energy to be absorbed – Primarily collisions with inner shell electrons which are lithology DEPENDENT

• Scattering & absorption result in a wide

range of gamma energy levels at the tool’sdetectors

Formation

Spectral Density – physics


http://slidepdf.com/reader/full/ttp-density-nt-rev2 7/23Internal Use Only

• Just like the GTET…

• Except - Two detectors: short-spaced (which is more sensitive to standoff interactions)

and long-spaced (which is more sensitive to formation interactions)


Photo-Multiplier Tube

High

Voltage

High

Voltage

Scintillation

Crystal

Scintillation

Crystal

Optical

Grease

Optical

Grease

Photo-Sensitive

Cathode

Photo-Sensitive

Cathode

Dynodes Collection

Anode

SDLT gain stabilizer source (Cs-137)









• Only W1 – W4 are used to processb

and Pe

• Remaining count rates used to compensate for shifts in spectrum

caused by temperature variations




For each window, count-rate is related to electron density by…

LnC = a1 + a2ρe + a3ρe2 + a4ρe

3 + a5L + a6x4 + a7x5

Bulk density is related to electron density by…b = 1.0704 e – 0.1883

Porosity is related to Bulk density by…


ma – b)

ma – fl)D =



• Density of the actual formation rock• Commonly assumed matrix densities ( ma)

Sandstone: 2.65 gm/cc

Limestone: 2.71 gm/cc

Dolomite: 2.87 gm/cc

• Represent pure lithology at zero-porosity




• Density formation fluid occupying the pore space*

• Commonly assumed fluid densities ( fl)

Fresh water-based: 1.0 gm/ccSalt water-based: 1.1 gm/cc

*Represents the fluid present within pores of the volume of

investigation




• Remember - Gamma ray absorption is related toelements present in the rock so…

• Photoelectric factor (Pe) can be used to help identify

rock type, even in complex lithology




• Compositionally pure formations have characteristic values of Pe

PeMATERIAL

1.81

5.08

3.142.5 – 3.5

5.05

4.65

~ 0.2

266.82

Sandstone

Limestone

DolomiteShales

Anhydrite

Halite

Coal

Barite




• Count rate is a function of…

formation density

L formation lithology

mc mudcake densityLmc mudcake lithology

tmc mudcake thickness

tmc

Lmc L

mc

Formation

M u d c a k e




• Detectors may not be in direct contact with formation




• Stand-off causes differences between computed bulk density and true

formation density

• Real-time correction is applied to compensate for stand-off

• Corrections…

DRHO (old) density correction

CORP - correction plus

contrast between the density of the formation and the density of the mud

• CORM - correction minuscontrast between the Pe of the formation and the Pe of the mud




• Caliper Measurement

utilizing the pad and backuparm.

• Calculate AHV & BHV

• Permeability Indicator

– Caliper readings less than

bit size may indicate a

permeable zone.

Spectral Density – Caliper



Spectral Density – calibration

Calibration forces the tool to measure

the same density as the standard tool

in the same material (aluminum and

magnesium)

Transfer standard

Calibration ensures

Accurate values of ρb

All* density tools measure the

same response in the same

formation and under the same

borehole conditions

* both internal and competitors!

Al = 2.698 gm/cc

Mg = 1.783 gm/cc



Spectral Density – response

• Fluid and lithology effects

Actual

Ф = 25%

In all cases

Fluid Density Tool



Fluid Density Tool• Used in Production Logging to determine the density of fluid in the casing wellbore

Review



Review• Understand and identify the applications of the spectral density tool

• Understand and explain the basic physics involved in the measurements of the spectral density

tool including various gamma energies and their corresponding interaction with matter

• Understand the theory of gamma emitting sources, detectors and PM tubes (including voltagestabilization for temperature), and the use of windows for energy level measurements.

• Identify the output by the spectral density tool and explain how each is determined

• Identify the depth of investigation and vertical resolution of the SDLT

• Identify the wellbore environments the spectral density tool will function properly in

• Understand the wellbore parameters which interfere with spectral density tool quality (requirecorrections)

• Understand the spectral density tool response versus borehole and formation environment

• Identify the matrix density and Pe values for Sandstone, Limestone, Dolomite, Shale

• Understand the parameters and calculate density porosity from a bulk density measurement

• Understand the difference between the effect of gas versus the effect of incorrect matrix densityvalue

• Identify the master calibration standard, the transfer standard for shop calibrations, and what is

utilized for field calibrations

Documents

TTP Density NT Rev2