01b- QL Interpretation

7/31/2019 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.

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01b- QL Interpretation