Upload
devananda-narah
View
246
Download
0
Embed Size (px)
Citation preview
8/13/2019 Pete 663 Lect Pass Sp
1/47
PASSIVE MEASUREMENTS - SP
FORMATION EVALUATION
PETE 663
Summer 2010
Dr. David Schechter
8/13/2019 Pete 663 Lect Pass Sp
2/47
-HEADING
Well location
Depth references
W
ell depth
Date of log
Casing shoe depth
Bit size
Mud data
Type
Properties
Resistivities
Max. Temperature
8/13/2019 Pete 663 Lect Pass Sp
3/47
DRILLING DISTURBS
FORMATION Drilling and rock crushing Damage zone
Mud systems and invasion Oil based mud
Small conductivity mud
Shallow invasion Thin cake
Water based mud
Moderate to very conductivemud
Shallow to deep invasion Thin to thick cake
Mudcake
Invading filtrate
Damaged zone
8/13/2019 Pete 663 Lect Pass Sp
4/47
MUD FILTRATE INVASION
Modif ied from J. Jensen, PETE 321 Lecture Notes
WellboreMud
(Rm)
Mud Cake(Rmc)
Uninvaded
Zone
(Rt)
InvadedZone (Rxo)
UninvadedZone
(Rt)
8/13/2019 Pete 663 Lect Pass Sp
5/47
Borehole
Rm : Borehole mud resistivity
Rmc : Mudcake resistivity
Invaded zone
Rmf : Mud filtrate resistivity
Rxo : Invaded zone resistivity
Sxo : Invaded zone water saturation
Uninvaded zone
Rw : Interstitial water resistivityRt : Uninvaded zone resistivity
Sw : Uninvaded zone water saturation
COMMON TERMINOLOGY
8/13/2019 Pete 663 Lect Pass Sp
6/47
PASSIVE MEASUREMENTS
Caliper
Spontaneous Potential Gamma Ray
Natural Spectral
8/13/2019 Pete 663 Lect Pass Sp
7/47
CALIPERS
Uses Hole volume Mudcake (permeability)
Tool corrections Crude lithology indicator
Properties
Two, three, or four arms Linked or independent
Calipers may disagree(limitations)
Non-circular hole Deviated wells
Two-arm caliper
actual
apparent
Three-arm caliper
actual
apparent
arm
arm
8/13/2019 Pete 663 Lect Pass Sp
8/47
8/13/2019 Pete 663 Lect Pass Sp
9/47
SP DEFINITION
SP is a natural occurring electrical potential
relative to a surface potential measured in the
borehole mud
Potentials are created by chemically induced
electric current
The potential of the surface reference must
remain constant
8/13/2019 Pete 663 Lect Pass Sp
10/47
USES OF SP
1. Determine values of formation water
resistivity
2. Identify permeable zones
3. Qualitative indication of shale
content
4. Define bed boundaries
5. Well-to-well correlation
8/13/2019 Pete 663 Lect Pass Sp
11/47
SPONTANEOUS POTENTIAL (SP)
Uses Correlation
Lithology Shaliness indicator Depositional environment
indicator
Properties Measures formation voltage
Passive measurement
Ransom, PFE
++++
----+
+++
-12mV
+59mV
-71mV
POROUS,
PERMEABLE
BED
SHALE
SHALE
8/13/2019 Pete 663 Lect Pass Sp
12/47
8/13/2019 Pete 663 Lect Pass Sp
13/47
One electrode
Insulators on
either side
Surface ground
electrode at a
stable potential
THE SP TOOL
SHALE
SHALE
SAND
8/13/2019 Pete 663 Lect Pass Sp
14/47
SP PRINCIPLES
Must have water-based mud
Mud--formation watersalinity difference causes
battery effect
Battery effect components
Electrochemical
Liquid Junction Potential, Ej
In permeable region
Anions more mobile than cations
Membrane Effect, Em Shale acts as membrane
Repels anions / passes cations
Electrokinetic (Streaming)
Usually minor, disregarded
Electrochemical Effect
Membrane effect
SAND
SHALE
Flushed
Zone
Less SaltyWater
Virgin
Zone
SaltyWater
Membrane effect
VirginZone
+
++++
8/13/2019 Pete 663 Lect Pass Sp
15/47
8/13/2019 Pete 663 Lect Pass Sp
16/47
LIQUID JUNCTION POTENTIAL
A liquid junction potential
develops when aconcentrated salt solution
(formation water ) is in
direct contact with adiluted salt solution (fresh
mud filtrate)
The net effect of morepositive ions in formation
water and more negative
ions in mud filtrate createspotential difference.
8/13/2019 Pete 663 Lect Pass Sp
17/47
MEMBRANE POTENTIAL, Em
Created when a
shale is introduced
between aconcentrated salt
solution(formation
water) and adiluted salt solution
(fresh mud filtrate)
8/13/2019 Pete 663 Lect Pass Sp
18/47
8/13/2019 Pete 663 Lect Pass Sp
19/47
TYPICAL SP RESPONSES
BASED ON THE
DIFFERENCE BETWEEN
Rw and Rmf.
5. Rmf Rw - Amplitude negative but
not large
1. Rmf >> Rw - Amplitude large andnegative
REVERSE
D
SP
NORMALSP
1
2
3
4
5
(+)
(-)
8/13/2019 Pete 663 Lect Pass Sp
20/47
STATIC SP (SSP)
If it were possible to prevent SP currents from
flowing and measure the potential of mud thiswould provide a value for the SSP
Conditions where the SSP is recorded directly:
1. Thick zones
2. Clean (no shale) zones
3. Only water bearing zones
4. Permeable zones
8/13/2019 Pete 663 Lect Pass Sp
21/47
SELECTING A 100% WATER SATURATED ZONE
Low resistivitysuggesting a
water bearing
formation
Low GR response and high SP deflection
8/13/2019 Pete 663 Lect Pass Sp
22/47
8/13/2019 Pete 663 Lect Pass Sp
23/47
PSEUDO- STATIC SP (PSP)
Presence of shale in the formation will
reduce the static SP Shale lattice will slow the migration of
chlorine ions and assist the flow of sodium
ions, decreasing Ej
This reduces SSP to a pseudo-static value,
PSP
The volume of shale can be calculated:
Vsh = 1- (PSP)/(SSP)
8/13/2019 Pete 663 Lect Pass Sp
24/47
EXAMPLE PROBLEM
8/13/2019 Pete 663 Lect Pass Sp
25/47
SP RESPONSE
IN THINBEDS
8/13/2019 Pete 663 Lect Pass Sp
26/47
USING THE SP EQUATION FOR
Rw DETERMIMATION - CLASSICAL METHOD
1. Determine formation temperature
2. Find Rmf at formation temperature
3. Convert Rmf at formation temperature to Rmfe value
4. Compute Rmfe / Rwe ratio from the SP
5. Compute the Rwe
6. Convert Rwe at formation temperature to Rw
8/13/2019 Pete 663 Lect Pass Sp
27/47
B
8/13/2019 Pete 663 Lect Pass Sp
28/47
THE SP EQUATION - 1
Define Essp = (Esp)max
We assume:
From electrochemical theory:
where Tf = formation temp, deg F
aw = formation water activity
amf = mud filtrate activity
Essp = max SP deflection, mV
)/(log)460(133.0 10 mfwfssp aaTE +=
)( mlssp EEE +
-20mV+
- 80 mV
- 60 mV
Shale
Clean
Sand
-20 mV
Shaly
Sand
Sandy
Shale
Shale
Essp
Shale
Baseline
B
THE SP EQUATION 2C
8/13/2019 Pete 663 Lect Pass Sp
29/47
THE SP EQUATION - 2
Difficult to measure activit ies Substitute resistivities for activit ies
For small salinities, a = 1/R For fresh mud f iltrate, assume
Rmfe = Rmf or
Rmfe = 0.85Rmf (Schlumberger)
For high salinities
Correction needed
Use Chart SP-2 (Schlumberger)
Use Chart SP-3 (Halliburton)
)/(log)273(24.0)/(log)460(133.0
10
10
wemfefssp
wemfefssp
RRTERRTE
+=
+=
Rw or Rmf
Rwe
or
Rmfe
C
EXAMPLED
8/13/2019 Pete 663 Lect Pass Sp
30/47
EXAMPLE
Determine Rmf @Tf (Arps Eq.) 5.6(11+21.5)/(33+21.5) = 3.3 m
Apply SP equation -50 = -0.24(33+273)log(3.3/Rwe)
Rwe = 0.68
Chart SP-2 gives Rw = 1.3 ohm-m(See next page)
D
10mV
-||+
Rmf = 5.6 m @ 11 CTf = 33 C
Determine Essp Shale base line
Maximum deflection line
Calculate deflection -50mV
Rarely knownUsually use charts, instead
F
8/13/2019 Pete 663 Lect Pass Sp
31/47
Rw or Rmf
Rw
e
orR
mfe
Rwe=0.68
Rw = 1.3
F
8/13/2019 Pete 663 Lect Pass Sp
32/47
PROBLEMThe SP deflection is 60 mV across a thick, water-
bearing, clean zone. The value of Rmf at that
temperature of 100 F is 0.5 ohm-m.Determine Rw at the same temperature (100 F)
Rw from SP: Classical MethodFirst, we determine the Rmfe (effective Rmf), since
the resistivity is not an accurate determination of
the ion activity that produces the SP.
Rw ESTIMATION FROM Rwe
8/13/2019 Pete 663 Lect Pass Sp
33/47
Rw ESTIMATION FROM Rwe
Rmfe = 0.45 ohm-mat 100 F.
Figure 9-13 in themanual.
1. Determine Rmfe
0.5,100F
0.45 ohm-m
Rmf, 0.5 ohm-m
R ESTIMATION FROM SSP
8/13/2019 Pete 663 Lect Pass Sp
34/47
2.
Determine
Rwe fromRmfe
Figure 9-14
of your
manual
Rmfe/Rwe = 7. Therefore,Rwe=0.45 ohm-m/7=0.064 ohm-m at 100 F
Rw ESTIMATION FROM SSP
60, 1007
SSP
8/13/2019 Pete 663 Lect Pass Sp
35/47
(Rwe=0.064 ohm-m at 100F)
3. Finally, determine Rw
Using Figure 9-13 of
your text again, wedetermine Rw=0.10
ohm-m at 100 F
Here, Rw
8/13/2019 Pete 663 Lect Pass Sp
36/47
THE SILVA-BASSIOUNI METHOD
Figure 9-
16 of your
text.
Rw ESTIMATION FROM Rwe
8/13/2019 Pete 663 Lect Pass Sp
37/47
For the same
problem as
before, ieRmf=0.5 ohmm
at 100 F,
determine Rw ifthe SP deflection
is 60 mV.
We see Rw=0.1
ohm-m, as shown
with the classical
method.
Figure 9-16 of
your text
145 mV 60 mV = 85mV
8/13/2019 Pete 663 Lect Pass Sp
38/47
8/13/2019 Pete 663 Lect Pass Sp
39/47
8/13/2019 Pete 663 Lect Pass Sp
40/47
ZONATION
8/13/2019 Pete 663 Lect Pass Sp
41/47
ZONATION
Zonation - Defines intervals of similar properties Purpose Well-to-well correlation Evaluation of specific intervals
Criteria Lithology Fluids Porosity and permeabili ty
Begin with coarse zonation Typically Well-to-well correlation 20 - 100 ft Detail evaluation 10 ft thick or more
Easy l ithologies first, e.g., shales Refine More subtle lithology changes Fluids in porous, perm intervals
Depends on measurements available
PASSIVE LOG CORRELATION
8/13/2019 Pete 663 Lect Pass Sp
42/47
PASSIVE LOG CORRELATION
GR, SP, and CAL Often correlate Different
measurements
Different reasons
Correlation helps
GR instead of SP inoil base mud
Easier detection ofshales Facilitates zonation
8/13/2019 Pete 663 Lect Pass Sp
43/47
SUMMARY
Drilling process affects formationAlters rock near wellbore
Invasion Passive logs respond to borehole,formation, and fluids
Caliper Simple measurement Care needed when interpreting and
comparing caliper
SP
Needs water based mud Estimates Rw
8/13/2019 Pete 663 Lect Pass Sp
44/47
8/13/2019 Pete 663 Lect Pass Sp
45/47
MEMBRANE POTENTIAL
8/13/2019 Pete 663 Lect Pass Sp
46/47
8/13/2019 Pete 663 Lect Pass Sp
47/47
LIQUID JUNCTION EFFECTS