Density LogDensity Log

Dr. Ir. Dr. Ir. DedyDedy KristantoKristanto, , M.ScM.Sc

FAMILY OF NUCLEAR TOOLSFAMILY OF NUCLEAR TOOLS

Density ToolsGR Tools Neutron Tools

GasOil

GR Neutrons

Natural GR Emitted GREmitted

Neutrons

ShalinessCorrelation

PorosityDensity

LithologyPorosity

Particle

Source

Application

NATURAL RADIOACTIVITYNATURAL RADIOACTIVITY

Spontaneous emission of α, β and γ particles from the nucleus of a atom

DENSITY LOGDENSITY LOG

• Uses radioactive source to generate gamma rays

• Gamma ray collides with electrons in formation, losing energy

• Detector measures reduced intensity of gamma rays

• Response of density tools is a function of the formation’s electron density

• Electron density is a measure of bulk density

DENSITY LOGDENSITY LOG

Bulk density, ρb, is dependent upon:– Rock lithology– Formation porosity– Density and saturation of fluids in pore

space

DENSITY PRINCIPLEDENSITY PRINCIPLEDetect GR’s from the source which have been

scattered back by the formation

FormationHydraulic

sonde

Caliperarm

Skid

Detectors

Gamma rayemitting source

Gamma rays

Low DensityWindows

CesiumSource

Stabilizer

TungstenBore Liner

Far Detector

Near Detector

TungstenShield

DENSITY PRINCIPLEDENSITY PRINCIPLE

• GR’s emitted into formation from source

• Detectors used to measure returning GR

• Energy level of returning GR measured

– High energy GR relate to - Density

– Low energy GR relate to - Lithology

EXAMPLE DENSITY LOGEXAMPLE DENSITY LOGGRAPI0 200

CALIXIN6 16

CALIYIN6 16

RHOBG/C32 3

DRHOG/C3-0.25 0.25

4100

4200

Caliper

Density correction

Gamma ray Density

DENSITY MEASUREMENTSDENSITY MEASUREMENTS

Pe

ρb ∆ρ• Uses– Porosity– Lithology

• Curves– Bulk density

(ρb and ∆ρ)– Pe

BUT WHY TWO DETECTORS?BUT WHY TWO DETECTORS?

• If the tool is to read the density correctly, all gamma rays must travel through the formation

• This is difficult due to mudcake and borehole mud

• To avoid mud, the detectors are pad mounted and press against the borehole wall.

• However, the mud cake is still present and therefore there are two detectors to compensate for it’s effect.

COMPENSATED TWO DETECTORCOMPENSATED TWO DETECTOR

Formation (ρb)

Long spacing detector

Short spacing detector

Mud cake(ρmc + hmc)

Source

Formation (ρb)

Long spacing detector

Long spacing detector

Short spacing detector

Short spacing detector

Mud cake(ρmc + hmc)

SourceSource

Source : 662 KeV Cs-137 gamma ray source.

Two detectors : Short spaced and the long spaced.

Source and detectors are pad mounted to give contact with the borehole wall.

Sandstone

ShaleCoal

Shale

Limestone

Shale

NPHI (v/v) 00.6Density (gr/cc) 2.71.7NPHI (v/v) 00.6 NPHI (v/v) 00.6

Density (gr/cc) 2.71.7 Density (gr/cc) 2.71.7

DENSITY LOG RESPONSE DENSITY LOG RESPONSE APPLICATIONSAPPLICATIONS

To determine bulk density and fluids densityCoal

NPHI (v/v) 00.6Density (gr/cc) 2.71.7NPHI (v/v) 00.6 NPHI (v/v) 00.6

Density (gr/cc) 2.71.7 Density (gr/cc) 2.71.7

Water

Gas Oil

BULK DENSITY INTERPRETATIONBULK DENSITY INTERPRETATION

• The bulk density (in gm/cc) is the weighted sum of the matrix and fluid densities

φρρφρ −−= )1( ma flb

• Typical values• Matrix density 2.65 SS; 2.71 LS; 2.87 Dol• Fluid density

• 0.9 - 1 OBM and fresh WBM• 1.1 - 1.2 salty WBM

BULK DENSITY LOGBULK DENSITY LOGGRC

0 150SPCMV-160 40ACAL

6 16

ILDC0.2 200

SNC0.2 200

MLLCF0.2 200

RHOC1.95 2.95

CNLLC0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900Bulk Density

Log

RHOC1.95 2.95

POROSITY FROM DENSITY LOGPOROSITY FROM DENSITY LOG

• Porosity equation

fma

bmaρ−ρρ−ρ

=φ

( )xohxomff S1S −ρ+ρ=ρ• The fluid density equation

BULK DENSITY INTERPRETATIONBULK DENSITY INTERPRETATION

ρρρρ

φ−

−=

ma fl

ma bD

• Charts– POR-5 (S)– POR-10 (H)

• Rearranging the equation gives porosity

BULK DENSITY INTERPRETATIONBULK DENSITY INTERPRETATION• The ∆ρ curve is “measurement quality”• Poor pad contact gives ∆ρ > 0.05• Often correlates with caliper

∆ρ

-0.25 0 +0.25

CAL

FACTORS AFFECTINGFACTORS AFFECTINGDENSITY LOG RESPONSEDENSITY LOG RESPONSE

• Borehole and mud filtrate effects– ρmf can be measured– Sxo can be calculated from shallow resistivity

logging tool• Shales and clays

– Vsh and ρsh can be obtained from log readings in shale zones

• Hydrocarbons– In oil zones, ρhc = ρo which can be measured from

fluid samples– In gas zones, ρhc = ρg which can be measured or

calculated using gas properties

PHOTOELECTRIC INTERPRETATIONPHOTOELECTRIC INTERPRETATION

• The Pe value (in barns/electron) is the weighted sum of the matrix and fluid capture cross sections

flma

flflmama

ee

eeeee

PPP

φρρφ

φρρφ

+−

+−=

)1(

)1(

• Typical Values• Matrix Pe: 1.8 SS; 5.1 LS; 3.1 DOL• Matrix ρePe: 4.8 SS; 13.8 LS; 9 DOL• Fluid ρePe:

• 0.1 - 0.4 OBM and fresh WBM• 0.4 - 1 salty WBM

PHOTOELECTRIC INTERPRETATIONPHOTOELECTRIC INTERPRETATION

•• The logging curve is The logging curve is PePe•• The product The product ρρeePePe = U, capture cross= U, capture cross--section/ccsection/cc

flma UUU φφ +−= )1(

• This looks like the density equation• We don’t solve for φ because Ufl << Uma

TYPICAL FORMATIONSTYPICAL FORMATIONS

Sandstone

Limestone

Dolomite

PEFRHOB

0 1032

2.65

2.87

2.715.1

3.1

1.8

TYPICAL VALUESTYPICAL VALUES

WIRELINE TOOL HISTORYWIRELINE TOOL HISTORY

Three-Detector Lithology Density (TLD)

Powered Gamma Tool (PGT)

Nal(TI)Scintillation DetectorGeiger-Muller DetecterGamma Ray Source

Nal(TI) Scintillation DetectorNal(TI) Scintillation DetectorGamma Ray Source

Nal(TI) Scintillation DetectorNal(TI) Scintillation DetectorGSO(Ce) Scintillation DetectorGamma Ray Source

Litho Density Tool (LGT)

Flex Joint

FlexJoint

DENSITY SUMMARYDENSITY SUMMARY

• Very reliable tool• Shallow depth of investigation - 10 to

15 cm• Wireline tool caliper reads dh - hmc• Logging While Drilling (LWD) version

has sonic caliper