02 - Density Flashcards
Definition
density
rho = m / V
in kg / m³
bulk density
rho_r
mean density of considered rock volume incl. pores
-> whole rock
density of any individual component i
rho_i
-> mineral like quartz
mean density of solid matrix material
rho_ma
density of matrix without pore fluid
mean density of pore (fracture) fluid
rho_fl
density of fluid e.g. water
bulk density
of composite material:
rho_r = sum(rho_i*V_i)
porous rock
pore space fraction
rho = (1 - phi) * rho_ma + phi * rho_fl
phi = total porosity
density measurement
with ..
for..
by ..
mechanism?
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
He-Pycnometry
- step
fill sample chamber while 2. Volume is closed
-> p1, Vcell, Vsample
-> n,R,T constant - step
open 2. Volume and close 3. Volume
-> Vadd, p2
-> rest known
ideal gas equation
n * R * T = p * V
Density of pore fluids
controlled by .. (3)
- chemical composition (+soluble components)
- temperature (v with ^density)
- pressure (^ with ^density)
API
American Petroleum Institute oil gravity number
for crude oils
API = 141.5 / rho_oil - 131.5
temperature density relation
If T increase
the density decrease
Density log
measures ..
device
principle
sketch slide 9
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
Density log
detectors (2)
long spacing detector:
- > less exact
- > more formation information
short spacing detector:
- > more precise
- > infos of mudcake etc.
Density log
typical logging sondes
use Cesium-137 source
066MeV gamma rays
-> compton scattering
Density log
critical points
electron density correlates strongly but not perfect with bulk density
gama ray cannot penetrate far into formation
-> small volume
Compensated density log
corrected effect of mud and mudcake
-> two or more detectors at different spacing from source
Compensated density log
short spacing means?
the shorter the spacing the shallower the depth of investigation
Dual energy CT scanning
scanned twice at two energy levels
Dual energy CT scanning
at > 100 kV
x-rays interact with matter
mainly compton scattering
amount of cs is sensitive to electron density bulk density
–> dark red = high density
Dual energy CT scanning
at < 100 kV
mainly photoelectric absorption
sensitive to effective bulk atomic number
–> dark red = high number & blue low number
Photoelectric absorption
emmision of electrons
Dual-energy CT scanning
example slide 11
bulk density
–> dark red = high density
bulk atomic number
–> dark red = high number & blue low number
