petrophysics - west virginia universitypages.geo.wvu.edu/~tcarr/petroleum/lecture...
TRANSCRIPT
Tim Carr - West Virginia University
Modified from SPWLA Website
PETROPHYSICS
PETROPHYSICS
GEOLOGY
DRILLING RESERVOIR
ENGINEERING
GEOPHYSICS
2
Electrical
Acoustic or Sonic
Nuclear
Geometry Hole Diameter – Rugosity
Direction – Inclination
Temperature
Pressure
3
Porosity - Φ
Permeability - K, Krel
Lithology/Mineralogy
Fluid & Gas Saturations - Sw, Sg, So
Resistivity/Electrical Properties
Sonic Properties (e.g., Strength)
Bed Contacts & Thickness
Fractures (Size, Frequency, Direction)
In-situ Stress 4
“True” Rt Formation Resistivity
Fluid Saturation Sw from Archie Equation from Archie Equation
Determination of Hydrocarbon-Bearing vs. Water-Bearing Zones
Geopressure Detection
Diameter of Invasion
Porosity
Correlation
Source Rocks/Gas Shale
5
Original Log
Various Types Electrode Logs
Laterologs
Focused Electrodes
Induction
Ohms Law E = Ir
6
Pechelbronn,
Alsace, France
September 5, 1927
SPWLA
7
∆𝐸 = 𝐼𝑟
Potential difference (volts) is equal to the current (amps) times the resistance (ohms)
8
Units – ohm-meter2/meter ohm-meter or ohm-m
Conductivity is Reciprocal of Resistivity – C=1/R 9
Resistivity of Water - Rw
Resistivity of Water and Formation
Resistivity of Water, Hydrocarbons,
and Formation
Resistivity of Formation
Incr
easi
ng R
esis
tivit
y
10
11
Normal Resistivity Tool
12
Induction (Conductivity) Tool
13
14
15
16
17
Log Presentation and Scales
18
Resistivity logs :
spherically-
focused (SFL),
medium
induction (ILM),
and deep
induction (ILD)
from
KGS Jones #1
19
20
21
High deep resistivity means:
Hydrocarbons
Tight streaks (low porosity)
Low deep resistivity means:
Shale
Wet sand
Separation between resistivities means:
The formation fluid is different from the drilling fluid
The formation is permeable to the drilling fluid
Deep, Medium, and Shallow refers to how far into the formation the resistivity is reading (4 ft, 2 ft, few in)
ILD (deep)
MSFL
SFL
Formation Fluid
different from
Drilling Fluid
Formation Fluid
similar to
Drilling Fluid
We will assume that this well was drilled with an water-based mud
Gamma Ray
Caliper
ILD (deep)
MSFL
SFL RHOB)
NPHI
• Using the Gamma Ray log, define a shale base line
• Deflections far to the left are sands
• Intermediate deflections to the left are silts
ILD (deep)
MSFL
SFL RHOB)
NPHI
Gamma Ray
Caliper
Sandstone
Sandstone
Sandstone
Siltstone
Shale
Siltstone
Shale
ILD (deep)
MSFL
SFL RHOB)
NPHI
Gamma Ray
Caliper
Sandstone
Sandstone
Sandstone
Siltstone
Shale
Siltstone
Shale
• Where is the neutron porosity to the right of the density porosity?
• This indicates where gas is in the sand pores
Gas
ILD (deep)
MSFL
SFL RHOB)
NPHI
Gas
Water?
Water?
Gamma Ray
Caliper
Sandstone
Sandstone
Sandstone
Siltstone
Shale
Siltstone
Shale
• Where do the resistivity logs give different values?
• This indicates where the fluids in the rocks differ from the drilling fluid
• In this case, it confirms the gas zone
Formation
Fluid
different
from
Drilling
Fluid
Water?
Water?
Formation Fluid
similar to
Drilling Fluid
F m=a
=o
R
R
wR
R Swo
t
I == n1
Sw=
am
*
wRt
1/n
( R )27
The keystone of log analysis for the solution of water saturation
of potential oil and gas zones (Archie, 1942)
The relationship of the resistivity of a water saturated rock (Ro) to its formation water resistivity (Rw) to the fractional porosity.
The ratio of the observed formation resistivity (Rt)
to its expected resistivity (Ro) if it was completely
saturated with water, to the fractional water saturation (Sw).
Archie, G. E.: "The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics", Petroleum Transactions of the AIME 146 (1942).
28
F = 1/ m
This is the first Archie equation,
where ‘m’ is known as the ‘cementation exponent’
Archie termed the ratio of Ro/Rw as the “formation
factor” which is denoted by F.
29
A
L
ro Rw
core plug
30
Archie (1942) observed the range in value of m in sandstones:
1.3 unconsolidated sandstones
1.4 - 1.5 very slightly cemented
1.6 - 1.7 slightly cemented
1.8 - 1.9 moderately cemented
2.0 - 2.2 highly cemented
Guyod gave the name “cementation exponent” to m, but noted that the pore geometry controls on m were more complex and went beyond simple cementation
31
0 1
Ro
Resistivity (Rt)
The ‘resistivity index’ (I) is defined as the ratio Rt/Ro
I = 1/Sw
Water saturation (Sw)
n
32
For water-wet rocks, n takes a value of about 2
For oil-wet rocks, n could be 9 or higher
33
Sw = [ (a / Øm)*(Rw / Rt) ](1/n)
Sw: water saturation
Ø: porosity
Rw: formation water resistivity - Rw=0.1
Rt: observed bulk resistivity
a: a constant (often taken to be 1)
m: cementation factor (varies around 1.8 to 2.2)
n: saturation exponent (generally 2)
34
35
Rt % Sw Sh
A 39 24 0.18 0.82
B 31 10 0.45 0.55
C 36 20 0.22 0.78
D 30 20 0.25 0.75
E 19 22 0.28 0.72
F 9 18 0.49 0.51
G 2 19 1.00 0.00
H 1.5 23 0.97 0.03
I 4.0 12 1.07 -0.07
J 7 10 0.95 0.05
Sw =
Rw
Rt.
1.8
Rw = 0.10 ohm-m
1/2
m = 1.8 n = 2.0
36
Well logs give us detailed information at the location of the borehole
If there are several wells in an area, we can correlate stratigraphic units between them
The correlation is based on ‘characteristics’ of the well log responses – like a fingerprint
Often we select a datum – a correlation horizon that is registered to a common depth (flattened)
There are two main ‘philosophies’ used in well log correlation:
Correlate based on lithologic units - Lithostratigraphy
Correlate based on assume time lines – Chronostratigraphy
Which is Better? A matter of heated debate!!
Well 5
Well 4
Well 3
Well 2
Well 1
We will look at the sediments deposited above a regional unconformity
regional
unconformity
Well 5
SP for
lithology
Resistivity for
time-correlation
Resistivity Markers
Base Map
Sh
ale
Ba
se
line
On one copy of the well log cross-section, identify the sand sitting above the regional unconformity (SP deflection to the left)
Correlate the logs based on lithology
Use the resistivity markers (A, B, C, …) to correlate time-equivalent horizons (hint: markers G and H do not extend all the way to Well 1)
QUESTION: Is the lithostratigraphic correlation and the chronostratigraphic correlation different?
40
Exercise Part 1 Based on the Log on Slide 35 and the Archie
Results of Slide 36, where would you complete the well (perforate). Give a depth range?
Exercise Part 2 Undertake the well correlation exercise
Slides 38-39
Logs are Important for Evaluating the Subsurface History – Schlumberger Brothers (1927)
Borehole Environment - Resolution
Reservoir Evaluation
Geosteering
Correlation Lithostratigraphic
Chronostratigraphic
Geologic Interpretation Lithology
Facies
Sequence Stratigraphy
41
42
Assignments
Reading for this week Ch. 7, pp. 307- 356, Selley
Complete the Log Exercises by Wednesday (3/18)
Archie
Correlation
Discuss Current Energy Events Read Today in Energy for Friday (3/13) at
http://www.eia.gov/
Be Prepared to Discuss in Class - Monday
Discussion Leader – Ethan Flanigan