Module 8-Density Logs

Question 1

How does the formation density log work?

Answer 1

bombards the formation with GR and measures electron density and porosity

Question 2

What are the two separate density values used to calculate porosity?

Answer 2

RHOb and RHOma

Question 3

What is RHOb?

Answer 3

the density of the entire formation(solid rock and fluid filled porosity parts) as measured by the logging tool.

Question 4

What is RHOma?

Answer 4

density of the solid framework of the rock without any porosity

Question 5

What does a litho-density tool measure?

Answer 5

Bulk density and the photo-electric effect (PE) and from it can determine lithology of a formation.

Question 6

What is the density log tool composed of?

Answer 6

a medium-energy GR source (cobalt 60, caesium 137, or an accelerator based source)

Question 7

How many GR detectors provide a measurement in a density log?

Answer 7

2

Question 8

What happens when the emitted GR collide with electrons?

Answer 8

They lose their energy and the scattered GR then returns to detectors in 2 energy ranges.

Question 9

What are the 2 energy ranges that the scattered GR return to detectors after collision and what do they relate to?

Answer 9

High energy GR- relate to Density

Low energy GR- relate to Lithology

Question 10

The returning higher energy range GR is affected by?

Answer 10

Compton scattering which is proportional to the electron density of the formation.

Question 11

The bulk density is related to?

Answer 11

Porosity

Question 12

The returning lower range GR is affected by?

Answer 12

by the photo electric effect

Question 13

What is the lower range GR strongly dependent on?

Answer 13

Lithology and very little on porosity

Question 14

An automatic mud cake compensation correction curve is often included as a quality control curve. What value must it not exceed to be considered reliable?

Answer 14

+ or - 0.15

Question 15

What are 4 applications of density logs?

Answer 15

Calculation of porosity
Lithology
Gas indication
Clay content

Question 16

Bulk densities of Sandstone, Limestone and Dolomite

Answer 16

Sandstone 2.65g/cc
Limestone 2.7g/cc
Dolomite 2.8 g/cc

Question 17

RHOmf?

Answer 17

density of the mud filtrate

Question 18

RHOh?

Answer 18

density of the hydrocarbon

Question 19

Sxo?

Answer 19

saturation of the flush zone

Question 20

Usual assumption of values for RHOf?

Answer 20

1 to 1.1

Will be less than 1 if gas is present

Question 21

What are the 2 types of density log tools?

Answer 21

Litho-density tools

FDC tools

Question 22

What is Pe log depth of investigation?

Answer 22

50-60cm. Defined by the distance between the long-spacing detector from the short spacing detector.

Question 23

Pe log application?

Answer 23

Determine lithology

Question 24

how are Pe logs better than GR to determine lithology

Answer 24

Pe can distinguish between clean sandstone and clean limestone

Question 25

What are the 10 factors affecting density logs?

Answer 25

1. Drilling mud
2. Borehole Shape
3. Presence of very thin bed
4. Presence of volcanic ash layer
5. Gas effect
6. Shale effect
7. Oil effect
8. Fractures effect
9. Over pressure effect
10. Unconformity effect