02 - Density

Question 1

Definition

density

Answer 1

rho = m / V

in kg / m³

Question 2

bulk density

Answer 2

rho_r

mean density of considered rock volume incl. pores

-> whole rock

Question 3

density of any individual component i

Answer 3

rho_i

-> mineral like quartz

Question 4

mean density of solid matrix material

Answer 4

rho_ma

density of matrix without pore fluid

Question 5

mean density of pore (fracture) fluid

Answer 5

rho_fl

density of fluid e.g. water

Question 6

bulk density

Answer 6

of composite material:

rho_r = sum(rho_i*V_i)

Question 7

porous rock

pore space fraction

Answer 7

rho = (1 - phi) * rho_ma + phi * rho_fl

phi = total porosity

Question 8

density measurement

with ..

for..

by ..

mechanism?

Answer 8

with pycnometer

for true volume of solid material

by employing Archimedes’ principle

using gas (helium) -> penetrates the finest pores
maximum accuracy -> 0.2 nm in diameter

Question 9

He-Pycnometry

Answer 9

1. step
   fill sample chamber while 2. Volume is closed
   -> p1, Vcell, Vsample
   -> n,R,T constant
2. step
   open 2. Volume and close 3. Volume
   -> Vadd, p2
   -> rest known

Question 10

ideal gas equation

Answer 10

n * R * T = p * V

Question 11

Density of pore fluids

controlled by .. (3)

Answer 11

• chemical composition (+soluble components)
• temperature (v with ^density)
• pressure (^ with ^density)

Question 12

API

Answer 12

American Petroleum Institute oil gravity number

for crude oils

API = 141.5 / rho_oil - 131.5

Question 13

temperature density relation

Answer 13

If T increase

the density decrease

Question 14

Density log

measures ..

device

principle

sketch slide 9

Answer 14

measures electron density of formation

device: contact tool emitting gamma rays

gamma rays collide with formation electrons and scatter
detetor count returning gamma rays
indicator for bulk density

Question 15

Density log

detectors (2)

Answer 15

long spacing detector:

• > less exact
• > more formation information

short spacing detector:

• > more precise
• > infos of mudcake etc.

Question 16

Density log

typical logging sondes

Answer 16

use Cesium-137 source

066MeV gamma rays

-> compton scattering

Question 17

Density log

critical points

Answer 17

electron density correlates strongly but not perfect with bulk density

gama ray cannot penetrate far into formation
-> small volume

Question 18

Compensated density log

Answer 18

corrected effect of mud and mudcake

-> two or more detectors at different spacing from source

Question 19

Compensated density log

short spacing means?

Answer 19

the shorter the spacing the shallower the depth of investigation

Question 20

Dual energy CT scanning

Answer 20

scanned twice at two energy levels

Question 21

Dual energy CT scanning

at > 100 kV

Answer 21

x-rays interact with matter

mainly compton scattering

amount of cs is sensitive to electron density bulk density
–> dark red = high density

Question 22

Dual energy CT scanning

at < 100 kV

Answer 22

mainly photoelectric absorption

sensitive to effective bulk atomic number
–> dark red = high number & blue low number

Question 23

Photoelectric absorption

Answer 23

emmision of electrons

Question 24

Dual-energy CT scanning

example slide 11

Answer 24

bulk density
–> dark red = high density

bulk atomic number
–> dark red = high number & blue low number