formation evaluation pete 321 · apparent neutron porosity (lspu) • similar layout to...
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FORMATION EVALUATION
PETE 321
Summer 2010
CROSSPLOTS(Porosity and Lithology)
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TWO-MEASUREMENT POROSITY CROSSPLOTS
• Two measurements determine two unknowns– Formations with one lithology
• Lithology• Porosity
– Formations of two known constituents• Can determine a more accurate value of porosity• Can determine the percentage of each mineral
– Complex lithologies• Can determine a more accurate value of porosity• Cannot determine percentage mineral makeup
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COMMON POROSITY CROSSPLOTS
• Neutron-density
• Sonic-neutron
• Sonic-density
• All have complicating effects– Shaliness– Hydrocarbons (gas)– Fractures
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NEUTRON-DENSITY CROSSPLOTS
• Most frequently used
• Developed for clean, liquid-saturatedformations
• Boreholes filled with water or water-based muds
• Several charts, depending on tools– CP-1’s Schlumberger– CNT-K-1’s and DSN-II-1’s Halliburton
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• Axes– Neutron limestone– Density
• NE-SW Lith. Lines– Sandstone– Limestone– Dolomite
NEUTRON DENSITY
CROSSPLOT
• NW-SE Por. Lines– Connect equal por pts– Nearly parallel
φ = 20
SulfurSalt
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
Trona
PolyhaliteLangbeiniteBul
k de
nsity
(Mm
g/m
3or
g/c
c)
403020100Apparent neutron porosity (lspu)
φ = 10
φ = 30
22%
2.45
A
B
C
% Ls = BC / AC% Dol = AB / AC
Matrix may be:• Ls and dolomite• Ss and dolomite
~2.83
-
SulfurSalt
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
Trona
PolyhaliteLangbeiniteBul
k de
nsity
(Mg/
m3
or g
/cc)
403020100Apparent neutron porosity (lspu)
CHART BASED on...– POR-12/13 Neutron
– POR-10 Density
-
SulfurSalt
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
Trona
PolyhaliteLangbeiniteBul
k de
nsity
(Mg/
m3
or g
/cc)
403020100Apparent neutron porosity (lspu)
• Parallel lith. lines– Constant separation– Distinct position
• Log presentation(next)
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• Parallel lith. lines– Constant separation– Distinct position– Log presentation
• Limestone scaling– Neutron 45 to -15 lspu– Density 1.95 to 2.95 g/cc– LS ρ and φ values overlie
in Ls
• Other scalings possible
|2.7
0|DENSITY-NEUTRON
PRESENTATION
φ=12 ss ρb =2.45; φn = 9
φ=30 ss ρb =2.15; φn = 27
φ=12 dol ρb =2.67; φn = 15
φ=30 dol ρb =2.33; φn = 33
φ=12 ls
ρb ~2.53φ=30 ls ρb ~2.23
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EXAMPLE LOG - WELL “X”• 90-260ft Zone D
– OWC @ 150ft– Pe = 1.8 - 2: SS– Den-Neut
• LS compatible• Ntrn to rt of Den• SS lithology• Large sep. above
150 ft
• Shales– Pe = 2.5 - 3– Neutron left of
Density
B
C
D
OWC
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OTHER EFFECTS
• ShalesSulfur
Salt
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
Trona
PolyhaliteLangbeiniteBul
k de
nsity
(Mg/
m3
or g
/cc)
403020100Apparent neutron porosity (lspu)
• Gas
• Fractures– No effect, both
logs respond tototal porosity
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EXAMPLE LOG - DN PLOT, WELL “X”
Shale Effect
Borehole effects and calcite stringers cause outliers
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WELL “X”DN PLOT(EXCEL)
Density-Neutron Response
1.9
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3-5 0 5 10 15 20 25 30 35 40 45
Neutron Porosity, limestone
Bul
k de
nsity
, g/c
c
Qtz Calcite DolomiteGR < 30 & ILD < 1 GR > 80 GR < 30 & ILD > 1
Shale plots like dol; use GR to differentiate
Oil
Water
Values do not all fallon Ss line owing to:
• Borehole effects
• Carbonate cements
• Shaliness
• HC vs water
• Statistical fluctuations of tools
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GAS EFFECT - 1WELL “A”
• Zone (depth)– A: 0 - 20– B: 20 - 45– C: 45 - 335– D: 335 - 350
• A– Low GR– Den = 2.95 (high)– Neut por. = -2
• B, D – high GR• C
– D-N litho scaling– GWC @ 290 ft.– D-N near overlay
below
A
B
C
D
LS Calibration
GasEffect
0
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GAS EFFECT - 2
WELL “A”
AB
D
C
A
D Shale
C
B Marl
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DENSITY-NEUTRON - OTHER COMMENTS
• Density log may be displayed as porosity
– Density-Neutron overlay for water- filled lithology
– Curve order as with g/cc scaling
• Shale/Gas effects
– Across litho lines: Lithology most affected
– Along porosity lines: Porosity least affected
• Response lines change with tool type
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COMMON POROSITY CROSSPLOTS
• Neutron-density
• Sonic-neutron
• Sonic-density
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SONIC-NEUTRON CROSSPLOTS
• Developed for clean, liquid-saturated formations
• Boreholes filled with water or water-base muds
-
t,So
nic
tran
sit t
ime
(μs/
ft)
110
100
90
80
70
60
50
40403020100
Syivite
Trona
Time average
Field observation
Apparent neutron porosity (lspu)
• Similar layout to density-neutron
• Two lines - two porosity models– Wylie time average– Raymer-Hunt-Gard.
• Charts– CP-2’s (S)– CNT-K-2’s (H)
SONIC-NEUTRON PLOTS - 1
-
110
100
90
80
70
60
50
40403020100
Syivite
Trona
t,So
nic
tran
sit t
ime
(μs/
ft)
Time averageField observation
Apparent neutron porosity (lspu)
• Shale - NE region
SONIC-NEUTRON PLOTS - 2
• Fracs - South
• Gas - NW
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WELL “X,” SN PLOT W/ GR
Sonic-Neutron (CNL), Fresh Mud
40
50
60
70
80
90
100
110
120
-5 0 5 10 15 20 25 30 35 40
Neutron, apparent LS pu
Soni
c sl
owne
ss, m
s/ft
Quartz Calcite Dolomite GR < 30 GR > 80
• Shaliness• Optimistic
porosity• Lithology OK
• HC effect slight
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COMMON POROSITY CROSSPLOTS
• Neutron-density
• Sonic-neutron
• Sonic-density• Poor porosity resolution• Useful for some evaporites
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SONIC-DENSITY CROSSPLOTS
• Poor lithology and porosity
• Multiple lines– WTA
– RHG
• Useful for– Evaporites– Vsh
Density-Sonic ResponseField Lines Only
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
340 60 80 100
Sonic DT
Den
sity
Qtz Calcite Dolomite
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WELL “X,”DENSITY-SONIC
• Clean points cover all lines
• Shale point distinct
Density-Sonic Response
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
40 60 80 100
Sonic DT
Den
sity
Qtz Calcite Dolomite GR < 30 GR > 90
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MID PLOTS - 2 LOGS
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DENSITY-SONIC
Vsh
• Locate 100%shaleand cleanformation
• Grid to give Vsh
Density-Sonic Response
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
40 60 80 100
Sonic DT
Den
sity
Qtz Calcite Dolomite GR < 30 GR > 90
Vsh = 1
Vsh = 0What is shale content of
formation comprisedof 2 minerals?
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MID PLOTSPRINCIPLES
• Lith. lines– 3 of many poss.– Each line diff. lith.
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
Bul
k de
nsity
(Mg/
m3
or g
/cc)
403020100Apparent neutron porosity (lspu)
• Line definition– Use endpoint loc’n– Value of ρb for φ = 0– Called ρmaa
ρmaa= 2.68
ρb= 2.30, φn = 21
• ExampleLogs show ρb= 2.30, φn = 21
ρmaa = 2.68
1. DETERMINE APPARENT MATRIX DENSITY
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MID PLOTSPRINCIPLES
• Lithology Lines– Similar to D-N
• Line Definition– Use endpoint loc’n– Value of Δt for φ = 0– Called Δtmaa
• ExampleLogs show Δt = 78, φn = 21
Δtmaa = 53
110
100
90
80
70
60
50
40403020100
Syivite
Tronat,
Soni
c tr
ansi
t tim
e (μ
s/ft)
Field observation
Apparent neutron porosity (lspu)
Δt = 78, φn = 21
Δtmaa= 53
2. DETERMINE APPARENT MATRIX TRANSIT TIME
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THREE - MEASUREMENT CROSSPLOTS
• For lithology determination only• Used when 3 porosity logs available• Three types
– Density-Neutron-Sonic (M-N plot)– Density-Neutron-Sonic (MID plot)– Density-Neutron-Pe (Umaa -- ρmaa plot)
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MID PLOTS PRINCIPLES
• 3 Lithology Points
Results– 50% quartz– 50% calcite
• Exampleρmaa = 2.68Δtmaa = 53 Quartz
Dolomite
Calcite
Δtmaa
Ρ maa
3. DETERMINE LITHOLOGY
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Calculating Δtmaa and ρmaa• At each depth: Δt, ρb, and φn• 1. Obtain φDN and φSN from crossplots• 2. ρmaa = (ρb − φDNρfl)/(1 - φDN)• 3. Δtmaa = Δt − (φSNΔt)/0.7
– 0.7 factor may vary somewhat
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SUMMARY• 3 types of porosity logs
• Density, Neutron, Sonic
• These logs respond differently to matrix, fluids and pore types
• Use for 2-log crossplots
• Crossplots allow determination of porosity and proportions of 2 minerals, if mineralogy is known
• Neutron – density is most commonly used crossplot
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SUMMARY
• 3-Log Crossplots– Lithology only– Several versions
• MID plot• MN plot• Umaa -- ρmaa plot
FORMATION EVALUATION��PETE 321TWO-MEASUREMENT POROSITY CROSSPLOTSCOMMON POROSITY CROSSPLOTSNEUTRON-DENSITY CROSSPLOTSNEUTRON DENSITY CROSSPLOTSlide Number 6Slide Number 7Slide Number 8EXAMPLE LOG - WELL “X”OTHER EFFECTSEXAMPLE LOG - DN PLOT, WELL “X”WELL “X”�DN PLOT�(EXCEL)GAS EFFECT - 1�WELL “A”GAS EFFECT - 2�WELL “A”DENSITY-NEUTRON - OTHER COMMENTSCOMMON POROSITY CROSSPLOTSSONIC-NEUTRON CROSSPLOTSSlide Number 18Slide Number 19WELL “X,” SN PLOT W/ GRCOMMON POROSITY CROSSPLOTSSONIC-DENSITY CROSSPLOTSWELL “X,” �DENSITY-SONICSlide Number 24DENSITY-�SONIC�VshMID PLOTS�PRINCIPLESMID PLOTS�PRINCIPLESTHREE - MEASUREMENT CROSSPLOTSMID PLOTS PRINCIPLES�Calculating Dtmaa and rmaa Slide Number 31SUMMARY
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