01b- QL Interpretation
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Transcript of 01b- QL Interpretation
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Copyrght 2003, NExT 1
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Quick-Look Log Interpretation
E. Standen
NExT Training
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B a s a l Q u a r tz N o . 10 6 / 2 8 / 2 0 0 2 1 0 : 0 2 : 0 6 A M
D E P T H
F T
1 : 5 0 0
G R ( G A P I)0 . 1 5 0 .
C A L I ( IN )6 . 1 6 .
S P (M V )- 2 0 0 . 0 .
IL D ( O H M M )0 . 2 2 0 0 0 .
IL M ( O H M M )0 . 2 2 0 0 0 .
S F L ( O H M M )0 . 2 2 0 0 0 .
P H ID ( V / V )0 . 4 5 - 0 . 1 5
P H IN S S ( V / V )0 . 4 5 - 0 . 1 5
5 4 0 0
5 5 0 0
5 6 0 0
Basal Quartz Example Valley Fill SequenceRmf = 2.6 @ 60F, BHT = 130F
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Rock Matrix, Porosity & Fluids
Rt = Rw
Ro = F Rwwhere
F = a /m
Rt = Ro Rt = F Rw / Sw2
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Archies Equation
n
t
m
w
wR
RaS
Watersaturation,
fractionw
S
Resistivity of
formation water,
-mwR
Resistivity of
uninvaded
formation, -m
tR
Porosity,
fraction
Empirical constant
(usually near unity)
a
Saturation
exponent
(also usually
near 2)
nCementation
exponent
(usually near 2)m
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Resistivity & Lithology - Saturation
Low Resistivity is a water-wet formation.
Wet Sands/Carbonates
Shale
High Resistivity is a formation with no
water. Low Porosity no water
Hydrocarbon present low volume of water (Swirr)
Or, VERY FRESH water
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Clean
Low Resistivity => Water-Wet
High Resistivity => HC
Hydrocarbon Identification from Resistivity and SP.
or Tight?
(check)
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Quick-look HC Identification
& Flow Unit Analysis Highlight the deep resistivity log.
Highlight Sonic or Density log as Porosity. Both Sonic and Density read higher in Gas
In a porous, wet zone (ie. Low Resistivity and
High Porosity) overlay the porosity on the deep
resistivity log, keeping the logs parallel and on
depth.
Hydrocarbon is indicated where separation occurs
high resistivity and high porosity.
If you change the relative position of the porosity
and resistivity curves it implies a change in Rw.
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Trace Density or
overlay on a light
table.
Gamma Ray Neutron Density Porosity Log
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Overlay
Logs Here
Since we are dealing with log-compatible overlay scales, the density curve
on the resistivity scale now defines Ro, the wet resistivity of the formation.
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Water Wet
HC
hc
hc?
hc?
Water
Water Wet
HC
HC
5400
5500
5600
1
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Sw Calculations
Get Rw from the SP or Rwa in a 100% wet zone.
Compute Sw from Deep Resistivity and Density or
Sonic porosity.
Or
Compute Sw from Deep Resistivity and the average of
Neutron and Density porosity total).
Do not mix porosities in your computations.
If shale resistivity is much lower than Rt in the
hydrocarbon zone, be aware that no correction for the
shale effect on Rt has been made and you should
consider a shaly-sand interpretation model. An alternative to individual computations is to plot
porosity and resistivity on a Picket Plot.
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Rwa Method
Rwa is the apparent water resistivity
assuming all zones are 100% wet.
If Sw = 100% then: Rwa = **2 x Rt
If the zone is 100% wet then Rwa will go to
a minimum value. If hydrocarbon is present then Rwa > Rw.
(Rwa will be less than Rw in low porosity zones!)
In hydrocarbon zones Sw = Rw/Rwa
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Rwa Computation for BQ ExampleUsing Rild and PhiD (density porosity)
Basal Quartz No.106/26/2002 5:09:08 PM
DEPTH
FT
1:500
GR(GAPI)0. 150.
CALI (IN)6. 16.
SP(MV)-200. 0.
ILD(OHMM)0.2 2000.
ILM(OHMM)0.2 2000.
SFL (OHMM)0.2 2000.
Rwa (ohmm)0.002 20.
PHID(V/V)0.45 -0.15
PHINSS (V/V)0.45 -0.15
5400
Rwa = .025 ohmmNote that where PhiD goes to zero
Rwa goes lower than Rw.
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Pickett Plot ILD vs PhiDBasal Quartz No.1
ILD / PHIDInterval : 5340. : 5608.
0.01
0.02
0.03
0.040.050.060.070.080.090.1
0.2
0.3
0.40.50.60.70.80.91.
PH
ID
0.01 0.1 1. 10. 100. 1000.ILD
0.
30.
60.
90.
120.
150.GR
446 points plotted out of 537Well Depths
Basal Quartz No.1 5340.F - 5608.F
M=2
Rw = 0.025 ohmm
Water zonesHydrocarbon
Zones plot above
Sw=100% line.
Sw=100%
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Simple Shaley-Sand Model
Irreducible
water
Bound water
Clean Sand Matrix (Quartz) HC
total = effective
In a clean sand the irreducible water volume is a function
of the surface area of the sand grains and therefore, the
grain size.
Clean Sand Matrix (Quartz)
effective
Clay +
Silt
totalIn a shaley-sand the addition of silt + clay usually decreaseseffective porosity due to poorer sorting and increases the
irreducible water volume with the finer grain size. In
addition, there is clay bound water that is non-effective
porosity that adds conductivity to the formation.
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Quick-Look Shaley-Sand Analysis
Sw = 1/ T**2 x Rw/Rt
total = (PhiN + PhiD)/2
effective = total x (1 Vsh)
In a clean formation PhiN = PhiD and Phi-Total is Phie.
In a shaley formation PhiN + PhiD / 2 usually increases slightlyas shale volume increases (Shale total porosity is usually higher
than the total porosity of a clean sand until significant
compaction occurs).
As shale increases Rt will decrease so the net effect on the
saturation computation is minimal as shale volume increases.
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Archies Equation
n
t
m
w
w
R
RaS
As Shale (clay) volume increases What is the effect on Sw?
Up to about 20% Vshale not much effect will be seen on Sw as long
as the porosity input is Total Porosity, not Effective porosity.
Total
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What is the volume of water in the formation?
Answer: Sw x = BVW
Assume basic Archie: Sw**2 = (1/**2) * Rw/Rt
Sw**2 x **2 = Rw/Rt
orSw*= Rw/Rt
Rt is on a logarithmic scale - it is inversely
proportional to BVW.
low Rt = high BVW and high Rt = low BVW.
As long as BVW is changing with porosity you
are not in the zone of irreducible water saturation.
Bulk Volume Water
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Assume ILD = Rt, then BVW is proportional to 1/Rt
Clean zone
Low
Resistivity
High Resistivity
Lowest BVW
Low BVW
High BVW
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= 19%Sw=100%
Sw=100% = 18%
= 19%
= 19%
= 6 to 15%
= 12%
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depth Phi Rt Sw BVW
5350 0.12 15 0.372678 447
5374 0.09 25 0.3849 346
5378 0.13 27 0.25641 333
5382 0.06 22 0.615457 369
5392 0.12 28 0.272772 327
5396 0.18 14 0.257172 463
5408 0.19 7 0.344555 655
5420 0.16 1.1 1.032154 1651
5428 0.15 1.5 0.942809 1414
5436 0.19 0.8 1.019206 1936
BVW as Cap. Pressure
0
500
1000
1500
2000
2500
5350
5378
5396
5420
depth
BVW
BVW
Water free production
Ellerslie Example BVW Computation
We could plot Sw vs. depth as well, but saturation varies more
with changes in porosity. BVW goes to a minimum when all
rock types reach Swirr and is therefore, an easier number to
use for determining water-free production.
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BVW related to Cap. Pressure
Sw
1000
Pressure
OrDepth
Swirr
Swirr x Porosity = BVW at
irreducible saturation
conditions. This means that
when BVW approaches a
low constant value for a
formation it will produce
water free above that point.
Above the Swirr point,
changes in BVW will
reflect changes in pore size
(grain size) or a change in
HC fluid content.
Remember that Swirr is
unique for each rock unit.SwirrLow BVW Hi BVW
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CapillaryPressure
from Log
Data
B a s a l Q u a r tz N o . 10 2 / 2 5 / 2 0 0 3 3 : 2 2 : 0 7 P M
D E P T H
F T
1 : 5 0 0
S W ( D e c )0 . 1 .
P H iT ( v / v )0 . 2 5 0 .
P H IE ( D e c )0 . 2 5 0 .
B V W ( D e c )0 . 2 5 0 .
V W C L ( De c )0 . 1 .
P H IE ( D e c )1 . 0 .
V S IL T ( D e c )0 . 1 .
5 4 0 0
5 5 0 0
5 6 0 0
1
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BVW Plot with Permeability K4Buckles Plot
K= {70* e**2[(1-Swi)/Swi]}**2
Rock unit 1
Rock unit 2
Water zone
Transition zone
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BVW Rules of Thumb
eg. For: Sw=20% & =30%, BVW=600
For water free production in clean zones
Carbonates: Oil : BVW= 150 to 400
Gas: BVW= 50 to 300
Course-grained Sands: Oil : BVW = 300 to 600
Gas : BVW = 150 to 300
Very fine-grained Sands Oil : BVW = 800 to 1200
Gas : BVW = 600 to 900
Note: This will depend on the position in the HCcolumn. Higher up gives a lower BVW.
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For our Sand Example
BVWirr ranges from 460 to 330.
Since we expect light oil & gas production
from the zone we can estimate that the rock
should be a coarse-grained sand.
Zones of higher BVW above the oil-watercontact would indicate finer grain-size rock
units.
Log saturations should match core capillary
pressure data for any given rock type.