13 porosity

continued on next page

201

Por

GeneralPorosity—Wireline, LWD

Sonic ToolPorosity Evaluation—Open Hole

PurposeThis chart is used to convert sonic log slowness time (∆t) values into those for porosity (φ).

DescriptionThere are two sets of curves on the chart. The blue set for matrixvelocity (vma) employs a weighted-average transform. The red set is based on the empirical observation of lithology (see Reference20). For both, the saturating fluid is assumed to be water with a velocity (vf) of 5,300 ft/s (1,615 m/s).

Enter the chart with the slowness time from the sonic log on the x-axis. Move vertically to intersect the appropriate matrix velocityor lithology curve and read the porosity value on the y-axis. For rockmixtures such as limy sandstones or cherty dolomites, intermediatematrix lines may be interpolated.

To use the weighted-average transform for an unconsolidated sand,a lack-of-compaction correction (Bcp) must be made. Enter the chartwith the slowness time and intersect the appropriate compactioncorrection line to read the porosity on the y-axis. If the compactioncorrection is not known, it can be determined by working backwardfrom a nearby clean water sand for which the porosity is known.

Example: Consolidated FormationGiven: ∆t = 76 µs/ft in a consolidated formation with

vma = 18,000 ft/s.

Find: Porosity and the formation lithology (sandstone,dolomite, or limestone).

Answer: 15% porosity and consolidated sandstone.

Example: Unconsolidated FormationGiven: Unconsolidated formation with ∆t = 100 µs/ft in

a nearby water sand with a porosity of 28%.

Find: Porosity of the formation for ∆t = 110 µs/ft.

Answer: Enter the chart with 100 µs/ft on the x-axis and movevertically upward to intersect 28-p.u. porosity. Thisintersection point indicates the correction factor curveof 1.2. Use the 1.2 correction value to find the porosity forthe other slowness time. The porosity of an unconsoli-dated formation with ∆t = 110 µs/ft is 34 p.u.

Lithology vma (ft/s) ∆tma (µs/ft) vma (m/s) ∆tma (µs/m)

Sandstone 18,000–19,500 55.5–51.3 5,486–5,944 182–168Limestone 21,000–23,000 47.6–43.5 6,400–7,010 156–143Dolomite 23,000–26,000 43.5–38.5 7,010–7,925 143–126

Porosity—Wireline, LWD

Sonic ToolPorosity Evaluation—Open Hole Por-1

(customary, former Por-3)

30 40 50 60 70 80 90 100 110 120 130

Interval transit time, ∆t (µs/ft)

vf = 5,300 ft/s50

40

30

20

10

0

50

40

30

20

10

0

Porosity, φ (p.u.)

Porosity, φ (p.u.)

Time averageField observation

1.1

1.2

1.3

1.4

1.5

1.6

Dolomite

26,00

021

,000

18,00

0

vma(ft/s)

Bcp

23,00

019

,500

Calcite(lim

estone)

Quartzsandstone

202

Por

© Schlumberger

Por

203


Sonic ToolPorosity Evaluation—Open Hole Por-2

(metric, former Por-3m)

100 150 200 250 300 350 400

Interval transit time, ∆t (µs/m)

vf = 1,615 m/s50

40

30

20

10

0

50

40

30

20

10

0

Porosity, φ (p.u.)

Porosity, φ (p.u.)

1.1

1.2

1.3

1.4

1.5

1.6

Dolomite

8,000

6,400

5,500

5,950

vma(m/s)

Bcp


7,000

Calcite

Quartzsandstone

Dolomite

Calci

teQua

rtzsa

ndsto

ne

Cemen

ted qu

artz

sand

stone

PurposeThis chart is used similarly to Chart Por-1 with metric units.

© Schlumberger

204

Por

Por-3(former Por-5)

Density ToolPorosity Determination—Open Hole

PurposeThis chart is used to convert grain density (g/cm3) to density porosity.

DescriptionValues of log-derived bulk density (ρb) corrected for borehole size,matrix density of the formation (ρma), and fluid density (ρf) are usedto determine the density porosity (φD) of the logged formation. Theρf is the density of the fluid saturating the rock immediately sur-rounding the borehole—usually mud filtrate.

Enter the borehole-corrected value of ρb on the x-axis and movevertically to intersect the appropriate matrix density curve. From theintersection point move horizontally to the fluid density line. Followthe porosity trend line to the porosity scale to read the formation

porosity as determined by the density tool. This porosity in combina-tion with CNL* Compensated Neutron Log, sonic, or both values ofporosity can help determine the rock type of the formation.

ExampleGiven: ρb = 2.31 g/cm3 (log reading corrected for borehole

effect), ρma = 2.71 g/cm3 (calcite mineral), and ρf = 1.1 g/cm3 (salt mud).

Find: Density porosity.

Answer: φD = 25 p.u.

2.8 2.6 2.4 2.2 2.02.31

1.0 0.9 0.8

1.1

1.2

Porosity, φ (p.u.)

Bulk density, ρb (g/cm3)

ρ ma= 2.8

7 (dolomite)

ρ ma= 2.7

1 (calci

te)

ρ ma= 2.6

5 (quar

tzsa

ndsto

ne)

ρ ma= 2.8

3ρ ma

= 2.68

ρma – ρb

ρma – ρfφ =

ρf (g/cm3)

40

30

20

10

0


*Mark of Schlumberger© Schlumberger


205

Por

PurposeThis chart is used for the apparent limestone porosity recorded by theAPS Accelerator Porosity Sonde or sidewall neutron porosity (SNP)tool to provide the equivalent porosity in sandstone or dolomite for-mations. It can also be used to obtain the apparent limestone poros-ity (used for the various crossplot porosity charts) for a log recordedin sandstone or dolomite porosity units.

DescriptionEnter the x-axis with the corrected near-to-array apparent limestoneporosity (APLC) or near-to-far apparent limestone porosity (FPLC)and move vertically to the appropriate lithology curve. Then read theequivalent porosity on the y-axis. For APS porosity recorded in sand-stone or dolomite porosity units enter that value on the y-axis andmove horizontally to the recorded lithology curve. Then read theapparent limestone neutron porosity for that point on the x-axis.

The APLC is the epithermal short-spacing apparent limestoneneutron porosity from the near-to-array detectors. The log is auto-matically corrected for standoff during acquisition. Because it isepithermal this measurement does not need environmental correc-tions for temperature or chlorine effect. However, corrections formud weight and actual borehole size should be applied (see ChartNeu-10). The short spacing means that the effect of density andtherefore the lithology on this curve is minimal.

The FPLC is the epithermal long-spacing apparent limestone neu-tron porosity acquired from the near-to-far detectors. Because it isepithermal this measurement does not need environmental correc-tions for temperature or chlorine effect. However, corrections formud weight and actual borehole size should be applied (see ChartNeu-10). The long spacing means that the density and thereforelithology effect on this curve is pronounced, as seen on Charts Por-13and Por-14.

The HPLC curve is the high-resolution version of the APLC curve.The same corrections apply.

Example: Equivalent PorosityGiven: APLC = 25 p.u. and FPLC = 25 p.u.

Find: Porosity for sandstone and for dolomite.

Answer: Sandstone porosity from APLC = 28.5 p.u. and sandstoneporosity from FPLC = 30 p.u.

Dolomite porosity = 24 and 20 p.u., respectively.

Example: Apparent PorosityGiven: Clean sandstone porosity = 20 p.u.

Find: Apparent limestone neutron porosity.

Answer: Enter the y-axis at 20 p.u. and move horizontally to the quartz sandstone matrix curves. Move verticallyfrom the points of intersection to the x-axis and readthe apparent limestone neutron porosity values. APLC = 16.8 p.u. and FPLC = 14.5 p.u.

APS* Near-to-Array (APLC) and Near-to-Far (FPLC) LogsEpithermal Neutron Porosity Equivalence—Open Hole

Resolution Short Spacing Long Spacing

Normal APLCFPLCEpithermal neutron porosity (ENPI)†

Enhanced HPLCHFLCHNPI†

† Not formation-salinity corrected.

Porosity—Wireline

206

Por

Porosity—Wireline

APS* Near-to-Array (APLC) and Near-to-Far (FPLC) LogsEpithermal Neutron Porosity Equivalence—Open Hole Por-4

(former Por-13a)

40

30

20

10

0 0 10 20 30 40

Apparent limestone neutron porosity, φSNPcor (p.u.) Apparent limestone neutron porosity, φAPScor (p.u.)

True porosity for indicated

matrix material, φ (p.u.)

Calcite(lim

estone)

Dolomite

APLCFPLCSNP

Quartzsa

ndstone


Thermal Neutron ToolPorosity Equivalence—Open Hole

207

Por

GeneralPorosity—Wireline

PurposeThis chart is used to convert CNL* Compensated Neutron Log porositycurves (TNPH or NPHI) from one lithology to another. It can also beused to obtain the apparent limestone porosity (used for the variouscrossplot porosity charts) from a log recorded in sandstone or dolomiteporosity units.

DescriptionTo determine the porosity of either quartz sandstone or dolomiteenter the chart with the either the TNPH or NPHI corrected apparent limestone neutron porosity (φCNLcor) on the x-axis. Movevertically to intersect the appropriate curve and read the porosity for quartz sandstone or dolomite on the y-axis. The chart has a built-in salinity correction for TNPH values.

ExampleGiven: Quartz sandstone formation, TNPH = 18 p.u. (apparent

limestone neutron porosity), and formation salinity =250,000 ppm.

Find: Porosity in sandstone.

Answer: From the TNPH porosity reading of 18 p.u. on the x-axis,project a vertical line to intersect the quartz sandstonedashed red curve. From the y-axis, the porosity of thesandstone is 24 p.u.

40

30

20

10

0 0 10 20 30 40

Apparent limestone neutron porosity, φCNLcor (p.u.)

True porosityfor indicated

matrix material,φ (p.u.)

Quartz

sand

stone

Calcite(lim

estone)

Dolomite

Formation salinity

TNPH

NPHI

0 ppm

250,000 ppm

NPHI Thermal neutron porosity (ratio method)NPOR Neutron porosity (environmentally corrected and

enhanced vertical resolution processed)TNPH Thermal neutron porosity (environmentally corrected)

Por-5(former Por-13b)


208

Por

PurposeThis chart is used similarly to Chart Por-5 to convert 21⁄2-in. compen-sated neutron tool (CNT) porosity values (TNPH) from one lithologyto another. Fresh formation water is assumed.

Porosity—Wireline

Thermal Neutron Tool—CNT-D and CNT-S 21⁄2-in. ToolsPorosity Equivalence—Open Hole

40

30

20

10

0 –10 0 10 20 30 40

Sands

tone

DolomiteLim

estone

Apparent limestone neutron porosity (p.u.)



Por-6

© Schlumberger

209

Por

GeneralPorosity—LWD

adnVISION475* 4.75-in. Azimuthal Density Neutron ToolPorosity Equivalence—Open Hole Por-7

PurposeThis chart is used to determine the porosity of sandstone, limestone,or dolomite from the corrected apparent limestone porosity measuredwith the adnVISION475 4.75-in. tool.

DescriptionEnter the chart on the x-axis with the corrected apparent limestoneporosity from Chart Neu-31 to intersect the curve for the appropriateformation material. Read the porosity on the y-axis.

–5 0 5 10 15 20 25 30 35 40

40

35

30

25

20

15

10

5

0

Corrected apparent limestone neutron porosity, φADNcor (p.u.)



Quartz sandstone

Calcite (lim

estone)

Dolomite


210

Por

PurposeChart Por-8 is used similarly to Chart Por-7 for determining porosity from the corrected apparent limestone porosity from the adnVISION675 6.75-in. tool.

Porosity—LWD


–5 0 5 10 15 20 25 30 35 40

40

35

30

25

20

15

10

5

0


True porosity for indicated

matrix material, φ (p.u.)

Quartz sandstone

Calcite (lim

estone)

Dolomite


211

Por

PurposeChart Por-9 is used similarly to Chart Por-7 for determining porosity from the corrected apparent limestone porosity from the adnVISION825 8.25-in. tool.

Porosity—LWD


–5 0 5 10 15 20 25 30 35 40

40

35

30

25

20

15

10

5

0


True porosity (p.u.)

Sandstone

Limestone

Dolomite


212

Por

Porosity—Wireline

CNL* Compensated Neutron Log and Litho-Density* Tool (fresh water in invaded zone)Porosity and Lithology—Open Hole

PurposeThis chart is used with the bulk density and apparent limestoneporosity from the CNL Compensated Neutron Log and Litho-Densitytools, respectively, to approximate the lithology and determine thecrossplot porosity.

DescriptionEnter the chart with the environmentally corrected apparent neu-tron limestone porosity on the x-axis and bulk density on the y-axis.The intersection of the two values describes the crossplot porosityand lithology.

If the point is on a lithology curve, that indicates that the forma-tion is primarily that lithology. If the point is between the lithologycurves, then the formation is a mixture of those lithologies. The posi-tion of the point in relation to the two lithology curves as composi-tion endpoints indicates the mineral percentages of the formation.

The porosity for a point between lithology curves is determinedby scaling the crossplot porosity by connecting similar numbers onthe two lithology curves (e.g., 20 on the quartz sandstone curve to 20 on the limestone curve). The scale line closest to the point repre-sents the crossplot porosity.

Chart Por-12 is used for the same purpose as this chart for salt-water-invaded zones.

ExampleGiven: Corrected apparent neutron limestone porosity =

16.5 p.u. and bulk density = 2.38 g/cm3.

Find: Crossplot porosity and lithology.

Answer: Crossplot porosity = 18 p.u. The lithology is approxi-mately 40% quartz and 60% limestone.

213

Por


CNL* Compensated Neutron Log and Litho-Density* Tool (fresh water in invaded zone)Porosity and Lithology—Open Hole

Por-11(former CP-1e)

0 10 20 30 40Corrected apparent limestone neutron porosity, φCNLcor (p.u.)

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Bulkdensity,

ρb (g/cm3)

Densityporosity,φD (p.u.)

(ρma = 2.71 g/cm3,ρf = 1.0 g/cm3)

45

40

35

30

25

20

15

10

5

0

–5

–10

–15Anhydrite

SulfurSalt

ApproximategascorrectionPorosity

Calcite (lim

estone)

0

5

10

15

20

25

30

35

40

45

Quartz sandstone

0

5

10

15

20

25

30

35

40

Dolomite

0

5

10

15

20

25

30

35

Liquid-Filled Borehole (ρf = 1.000 g/cm3 and Cf = 0 ppm)


214

Por


PurposeThis chart is used similarly to Chart Por-11 with CNL CompensatedNeutron Log and Litho-Density values to approximate the lithologyand determine the crossplot porosity in the saltwater-invaded zone.

ExampleGiven: Corrected apparent neutron limestone porosity =

16.5 p.u. and bulk density = 2.38 g/cm3.


Answer: Crossplot porosity = 20 p.u. The lithology is approxi-mately 55% quartz and 45% limestone.

CNL* Compensated Neutron Log and Litho-Density* Tool (salt water in invaded zone)Porosity and Lithology—Open Hole

Por-12(former CP-11)

0 10 20 30 40

Corrected apparent limestone neutron porosity, φCNLcor (p.u.)

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Bulkdensity,

ρb (g/cm3)

Densityporosity,φD (p.u.)

(ρma = 2.71 g/cm3,ρf = 1.19 g/cm3)

45

40

35

30

25

20

15

10

5

0

–5

–10

–15

Liquid-filled borehole (ρf = 1.190 g/cm3 and Cf = 250,000 ppm)

0

5

10

15

20

25

30

35

40

45

0

5

10

15

20

25

30

35

0

5

10

15

20

25

30

35

40

45

Approximategascorrection

Porosity

Quartz sandstone

Calcite (limestone)

SulfurSalt

Dolomite

Anhydrite


215

Por


APS* and Litho-Density* ToolsPorosity and Lithology—Open Hole Por-13

(former CP-1g)

PurposeThis chart is used to determine the lithology and porosity from theLitho-Density bulk density and APS Accelerator Porosity Sonde porositylog curves (APLC or FPLC). This chart applies to boreholes filledwith freshwater drilling fluid; Chart Por-14 is used for saltwater fluids.

DescriptionEnter either the APLC or FPLC porosity on the x-axis and the bulkdensity on the y-axis. Use the blue matrix curves for APLC porosityvalues and the red curves for FPLC porosity values. Anhydrite plotson separate curves. The gas correction direction is indicated for for-mations containing gas. Move parallel to the blue correction line ifthe APLC porosity is used or to the red correction line if the FPLCporosity is used.

ExampleGiven: APLC porosity = 8 p.u. and bulk density = 2.2 g/cm3.

Find: Approximate quartz sandstone porosity.

Answer: Enter at 8 p.u. on the x-axis and 2.2 g/cm3 on the y-axisto find the intersection point is in the gas-in-formationcorrection region. Because the APLC porosity value wasused, move parallel to the blue gas correction line untilthe blue quartz sandstone curve is intersected at approx-imately 19 p.u.

Liquid-Filled Borehole (ρf = 1.000 g/cm3 and Cf = 0 ppm)

Bulk density,ρb (g/cm3)

Corrected APS apparent limestone neutron porosity, φAPScor (p.u.)

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0 0 10 20 30 40

APLCFPLC

Anhydrite

DolomiteCalcite (lim

estone)

Quartz sandstone

Porosity


0

5

5

10

10

15

15

20

20

25

25

35

3530

30

40

40

45

0

5

40

35

30

25

20

15

10

0

35

30

25

20

15 15

10

5

0

0

10

20

30

35

40

5

25


216

Por


PurposeThis chart is used similarly to Chart Por-13 to determine the lithologyand porosity from Litho-Density* bulk density and APS* porosity logcurves (APLC or FPLC) in saltwater boreholes.

ExampleGiven: APLC porosity = 8 p.u. and bulk density = 2.2 g/cm3.

Find: Approximate quartz sandstone porosity.

Answer: Enter 8 p.u. on the x-axis and 2.2 g/cm3 on the y-axis tofind the intersection point is in the gas-in-formation cor-rection region. Because the APLC porosity value wasused, move parallel to the blue gas correction line untilthe blue quartz sandstone curve is intersected at approx-imately 20 p.u.

APS* and Litho-Density* Tools (saltwater formation)Porosity and Lithology—Open Hole Por-14

(former CP-1h)

Liquid-Filled Borehole (ρf = 1.190 g/cm3 and Cf = 250,000 ppm)


Corrected APS apparent limestone neutron porosity, φAPScor (p.u.)

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.00 10 20 30 40

Anhydrite

Porosity


0

0

5

5

10

10

15

15

20

20

25

25

35

3530

30

40

40

45

0

5

40

35

30

25

20

15

10

0

40

35

30

25

20

15

10

5

0

4545

APLCFPLC

5

10

15

20

25

30

35

40

Quartz sandstone

DolomiteCalcite (limestone)


217

Por


adnVISION475* 4.75-in. Azimuthal Density Neutron ToolPorosity and Lithology—Open Hole Por-15

PurposeThis chart is used to determine the crossplot porosity and lithologyfrom the adnVISION475 4.75-in. density and neutron porosity.

DescriptionEnter the chart with the adnVISION475 corrected apparent lime-stone neutron porosity (from Chart Neu-31) and bulk density. Theintersection of the two values is the crossplot porosity. The positionof the point of intersection between the matrix curves represents therelative percentage of each matrix material.

ExampleGiven: φADNcor = 20 p.u. and ρb = 2.24 g/cm3.

Find: Crossplot porosity and matrix material.

Answer: 25 p.u. in sandstone.


1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Anhydrite

Salt


–5 0 5 10 15 20 25 30 35 40 45

Fresh Water, Liquid-Filled Borehole (ρf = 1.0 g/cm3)

DolomiteCalcite (lim

estone)Quartz

sandstone

Porosity

0

0

5

10

10

15

15

20

20

25

25

35

3530

30

40

40

40

35

30

25

20

15

10

5

05


Por

218


PurposeThis chart uses the bulk density and apparent limestone porosity fromthe adnVISION 6.75-in. Azimuthal Density Neutron tool to determinethe lithology of the logged formation and the crossplot porosity.

DescriptionThis chart is applicable for logs obtained in freshwater drilling fluid. Enter the corrected apparent limestone porosity and the bulkdensity on the x- and y-axis, respectively. Their intersection pointdetermines the lithology and crossplot porosity.

ExampleGiven: Corrected adnVISION675 apparent limestone porosity =

20 p.u. and bulk density = 2.3 g /cm3.

Find: Porosity and lithology type.

Answer: Entering the chart at 20 p.u. on the x-axis and 2.3 g /cm3

on the y-axis corresponds to a crossplot porosity of 21.5 p.u. and formation comprising approximately 60% quartz sandstone and 40% limestone.




1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0–5 0 5 10 15 20 25 30 35 40 45


DolomiteCalcite

(limestone)

Quartz sandstone

0

0

10

10

15

20

25

5

5

5

10

15

20

0

25

35

30

15

20

25

35

30

30

35

4 0

40

Porosity


219

Por


PurposeThis chart is used similarly to Chart Por-15 to determine the lithologyand crossplot porosity from adnVISION825 8.25-in. Azimuthal DensityNeutron values.




1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0–5 0 5 10 15 20 25 30 35 40 45


Calcite (lim

estone)

Quartz sandstone

0

10

5

Dolomite

5

10

15

20

0

25

35

30

15

20

25

35

30

40

0

10

15

20

5

30

35

40

25

Porosity 40


220

Por


Sonic and Thermal Neutron CrossplotPorosity and Lithology—Open Hole, Freshwater Invaded

PurposeThis chart is used to determine crossplot porosity and an approxi-mation of lithology for sonic and thermal neutron logs in freshwaterdrilling fluid.

DescriptionEnter the corrected neutron porosity (apparent limestone porosity)on the x-axis and the sonic slowness time (∆t) on the y-axis to findtheir intersection point, which describes the crossplot porosity andlithology composition of the formation. Two sets of curves are drawnon the chart. The blue set of curves represents the crossplot porosityvalues using the sonic time-average algorithm. The red set of curvesrepresents the field observation algorithm.

ExampleGiven: Thermal neutron apparent limestone porosity = 20 p.u.

and sonic slowness time = 89 µs/ft in freshwater drilling fluid.


Answer: Enter the neutron porosity on the x-axis and the sonicslowness time on the y-axis. The intersection point is atabout 25 p.u. on the field observation line and 24.5 p.u.on the time-average line. The matrix is quartz sandstone.

221

Por

GeneralGeneralPorosity—Wireline

Sonic and Thermal Neutron CrossplotPorosity and Lithology—Open Hole, Freshwater Invaded Por-20

(customary, former CP-2c)

0 10 20 30 40

110

100

90

80

70

60

50

40

Corrected CNL* apparent limestone neutron porosity, φCNLcor (p.u.)

Sonic transit time,∆t (µs/ft)

tf = 190 µs/ft and Cf = 0 ppm

Salt

Anhydrite

Dolomite

Calci

te (li

mesto

ne)

Quartz

sand

stone


Poros

ity

0

5

55

00

10

15

20

25

35

40

40

3535

30

3535

30

20

15

25

20

15

10

10

15

20

25

3030

0

5

10

10

15

15

20

2025

2530

30

0

5

0

5

25

10


222

Por


Sonic and Thermal Neutron CrossplotPorosity and Lithology—Open Hole, Freshwater Invaded

Por-21(metric, former CP-2cm)

0 10 20 30 40

360

340

320

300

280

260

240

220

200

180

160

140

Corrected CNL* apparent limestone neutron porosity, φCNLcor (p.u.)

Sonic transit time,∆t (µs/m)

tf = 620 µs/m and Cf = 0 ppm

Salt

Anhyd

rite

Dolomite

Calci

te (li

mesto

ne)

Quartz

sand

stone


Poros

ity

0

5

55

00

10

15

20

35

40

40

35

30

353530

20

15

10

25

20

15

10

10

15

20

3030

0

5

10

10

15

15

20

20

25

2530

30

0

5

0

5

2525

35

25

PurposeThis chart is used similarly to Chart Por-20 for metric units.



223

Por

GeneralGeneralPorosity—Wireline, LWD

Density and Sonic CrossplotPorosity and Lithology—Open Hole, Freshwater Invaded

PurposeThis chart is used to determine porosity and lithology for sonic anddensity logs in freshwater-invaded zones.

DescriptionEnter the chart with the bulk density on the y-axis and sonic slow-ness time on the x-axis. The point of intersection indicates the typeof formation and its porosity.

ExampleGiven: Bulk density = 2.3 g /cm3 and sonic slowness

time = 82 µs/ft.


Answer: Limestone with a crossplot porosity = 24 p.u.

224

Por


Density and Sonic CrossplotPorosity and Lithology—Open Hole, Freshwater Invaded Por-22

(customary, former CP-7)

40 50 60 70 80 90 100 110 120

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Sonic transit time, ∆t (µs/ft)


tf = 189 µs/ft and ρf = 1.0 g/cm3

Dolomite

Calcite

(limes

tone)

Anhydrite

Polyhalite

Gypsum

Trona

Salt

Sylvite

Sulfur

0

10

10

10 20

30

4040 40 40

40

3030

20

0

0

0

0

10

0

Porosity


30

30

30

2020

20

1020

10

Quartz

sand

stone

© Schlumberger

225

Por

General

PurposeThis chart is used similarly to Chart Por-22 for metric units.


Density and Sonic CrossplotPorosity and Lithology—Open Hole, Freshwater Invaded Por-23

(metric, former CP-7m)

150 200 250 300 350 400

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Sonic transit time, ∆t (µs/m)


tf = 620 µs/m and ρf = 1.0 g/cm3

Dolomite

Calcite

(limes

tone)

Anhydrite

Polyhalite

Gypsum

Trona

Salt

Sylvite

Sulfur

0

10

10

10 20

20

20

30

40

30

40 40

40

3030

20

0

0

10

0

Porosity

30

0

0

10


30

10

Quartz

sand

stone

20

20

40

© Schlumberger

226

Por


Density and Neutron ToolPorosity Identification—Gas-Bearing Formation

PurposeThis chart is used to determine the porosity and average water satu-ration in the flushed zone (Sxo) for freshwater invasion and gas com-position of C1.1H4.2 (natural gas).

DescriptionEnter the chart with the neutron- and density-derived porosity values(φNand φD, respectively). On the basis of the table, use the blue curvesfor shallow reservoirs and the red curves for deep reservoirs.

ExampleGiven: φD = 25 p.u. and φN = 10 p.u. in a low-pressure, shallow

(4,000-ft) reservoir.

Find: Porosity and Sxo.

Answer: Enter the chart at 25 p.u. on the y-axis and 10 p.u. on thex-axis. The point of intersection identifies (on the bluecurves for a shallow reservoir) φ = 20 p.u. and Sxo = 62%.

Depth Pressure Temperature ρw (g/cm3) IHw ρg (g/cm3) IHg

Shallow reservoir ~2,000 psi [~14,000 kPa] ~120°F [~50°C] 1.00 1.00 0 0Deep reservoir ~7,000 psi [~48,000 kPa] ~240°F [~120°C] 1.00 1.00 0.25 0.54

ρw = density of water, ρg = density of gas, IHw = hydrogen index of water, and IHg = hydrogen index of gas

227

Por

GeneralGeneralGeneralPorosity—Wireline, LWD

Density and Neutron ToolPorosity Identification—Gas-Bearing Formation Por-24

(former CP-5)

Neutron-derived porosity, φN (p.u.)

Density-derived porosity,φD (p.u.)

50

40

30

20

10

0 0 10 20 30 40

Sxo

Sxo

15

20

Porosity

30

80

35

025

40

55

15

10

20

100

30

25

60

40

60

20

100

80

35

40

20

0

10

For shallow reservoirs, use blue curves.For deep reservoirs, use red curves.

© Schlumberger

228

Por

General

PurposeThis chart is used to determine the porosity and average water satu-ration in the flushed zone (Sxo) for freshwater invasion and gas com-position of CH4 (methane).

DescriptionEnter the chart with the APS Accelerator Porosity Sonde neutron- anddensity-derived porosity values (φN and φD, respectively). On the basisof the table, use the blue curves for shallow reservoirs and the redcurves for deep reservoirs.

ExampleGiven: φD = 15 p.u. and APS φN = 8 p.u. in a normally pressured

deep (14,000-ft) reservoir.

Find: Porosity and Sxo.

Answer: φ = 11 p.u. and Sxo = 39%.

Porosity—Wireline

Density and APS* Epithermal Neutron ToolPorosity Identification—Gas-Bearing Formation

Depth Pressure Temperature ρw IHw ρg IHg

Shallow reservoir ~2,000 psi [~14,000 kPa] ~120°F [~50°C] 1.00 1.00 0.10 0.23Deep reservoir ~7,000 psi [~48,000 kPa] ~240°F [~120°C] 1.00 1.00 0.25 0.54

ρw = density of water, ρg = density of gas, IHw = hydrogen index of water, and IHg = hydrogen index of gas

229

Por

GeneralGeneralGeneralPorosity—Wireline

Density and APS* Epithermal Neutron ToolPorosity Identification—Gas-Bearing Formation Por-25

(former CP-5a)

Density-derived porosity,φD (p.u.)

For shallow reservoirs, use blue curves.For deep reservoirs, use red curves.

0 10 20 30 40

APS epithermal neutron-derived porosity, φN (p.u.)

50

40

30

20

10

0

55

1515

2020

40

3030

40

80

35

35

2525

40

20

0

100Sxo

Sxo

80100

200

6040

60

Porosity

1010


230

Por

General

PurposeThis nomograph is used to estimate porosity in hydrocarbon-bearingformations by using density, neutron, and resistivity in the flushedzone (Rxo) logs. The density and neutron logs must be corrected forenvironmental effects and lithology before entry to the nomograph.The chart includes an approximate correction for excavation effect,but if hydrocarbon density (ρh) is <0.25 g /cm3 (gas), the chart maynot be accurate in some extreme cases:

■ very high values of porosity (>35 p.u.) coupled with medium to high values of hydrocarbon saturation (Shr)

■ Shr = 100% for medium to high values of porosity.

DescriptionConnect the apparent neutron porosity value on the appropriateneutron porosity scale (CNL* Compensated Neutron Log or sidewallneutron porosity [SNP] log) with the corrected apparent densityporosity on the density scale with a straight line. The intersectionpoint on the φ1 scale indicates the value of φ1.

Draw a line from the φ1 value to the origin (lower right corner) of the chart for ∆φ versus Shr.

Enter the chart with Shr from (Shr = 1 – Sxo) and move verticallyupward to determine the porosity correction factor (∆φ) at the inter-section with the line from the φ1 scale.

This correction factor algebraically added to the porosity φ1 givesthe corrected porosity.

ExampleGiven: Corrected CNL apparent neutron porosity = 12 p.u.,

corrected apparent density porosity = 38 p.u., and Shr = 50%.

Find: Hydrocarbon-corrected porosity.

Answer: Enter the 12-p.u. φcor value on the CNL scale. A line fromthis value to 38 p.u. on the φDcor scale intersects the φ1

scale at 32.2 p.u. The intersection of a line from thisvalue to the graph origin and Shr = 50% is ∆φ = –1.6 p.u.Hydrocarbon-corrected porosity: 32.2 – 1.6 = 30.6 p.u.

GeneralGeneralPorosity—Wireline

Density, Neutron, and Rxo LogsPorosity Identification in Hydrocarbon-Bearing Formation—Open Hole

231

Por

GeneralGeneralGeneralPorosity—Wireline

Density, Neutron, and Rxo LogsPorosity Identification in Hydrocarbon-Bearing Formation—Open Hole Por-26

(former CP-9)

–5

–4

–3

–2

–1

0100 80 60 40 20 0

Shr (%)

∆φ (p.u.)

φDcor

50

40

30

20

10

0

φ1

50

40

30

20

10

0

φcor

(SNP)

50

40

30

20

10

0

φcor

(CNL*)

50

40

30

20

10

0

(p.u.)


232

Por


Hydrocarbon Density EstimationPor-27

(former CP-10)

1.0

0.8

0.6

0.4

0.2

0

φCNLcor

φDcor

0 20 40 60 80 100

0.8ρh

0.7

0.6

0.5

0.40.3

0.20.10

Shr (%)

1.0

0.8

0.6

0.4

0.2

0 0 20 40 60 80 100

0.8ρh

0.7

0.6

0.5

0.4

0.3

0.20.10

Shr (%)

φSNPcor

φDcor


PurposeThis chart is used to estimate the hydrocarbon density (ρh) within a formation from corrected neutron and density porosity values.

DescriptionEnter the ratio of the sidewall neutron porosity (SNP) or CNL* Compensated Neutron Log neutron porosity and density porosity corrected for lithology and environmental effects (φSNPcor or φCNLcor /φDcor, respectively) on the y-axis and the

hydrocarbon saturation on the x-axis. The intersection point of thetwo values defines the density of the hydrocarbon.

ExampleGiven: Corrected CNL porosity = 15 p.u., corrected density

porosity = 25 p.u., and Shr = 30% (residual hydrocarbon).

Find: Hydrocarbon density.

Answer: Porosity ratio = 15/25 = 0.6. ρh = 0.29 g /cm3.

13 porosity

Documents

po ros ity

neutron toolporosity

rxo logsporosity

ite dr hy

thermal neutron

freshwater

actual borehole

sonic transit