13 porosity
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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
Porosity—Wireline, LWD
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
Time averageField observation
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
Porosity—Wireline, LWD
*Mark of Schlumberger© Schlumberger
continued on next page
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
*Mark of Schlumberger© Schlumberger
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)
*Mark of Schlumberger© Schlumberger
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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.)
True porosityfor indicated
matrix material,φ (p.u.)
Por-6
© Schlumberger
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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.)
True porosityfor indicated
matrix material,φ (p.u.)
Quartz sandstone
Calcite (lim
estone)
Dolomite
*Mark of Schlumberger© Schlumberger
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
adnVISION675* 6.75-in. Azimuthal Density Neutron ToolPorosity Equivalence—Open Hole Por-8
–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.)
True porosity for indicated
matrix material, φ (p.u.)
Quartz sandstone
Calcite (lim
estone)
Dolomite
*Mark of Schlumberger© Schlumberger
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
adnVISION825* 8.25-in. Azimuthal Density Neutron ToolPorosity Equivalence—Open Hole Por-9
–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.)
True porosity (p.u.)
Sandstone
Limestone
Dolomite
*Mark of Schlumberger© Schlumberger
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
GeneralPorosity—Wireline
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)
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Por
GeneralPorosity—Wireline
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.
Find: Crossplot porosity and lithology.
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
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Por
GeneralPorosity—Wireline
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
Approximategascorrection
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
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Por
GeneralPorosity—Wireline
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)
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
3.00 10 20 30 40
Anhydrite
Porosity
Approximategascorrection
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)
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Por
GeneralPorosity—LWD
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.
Bulk density,ρb (g/cm3)
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
Corrected apparent limestone neutron porosity, φADNcor (p.u.)
–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
*Mark of Schlumberger© Schlumberger
Por
218
GeneralPorosity—LWD
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.
adnVISION675* 6.75-in. Azimuthal Density Neutron ToolPorosity and Lithology—Open Hole Por-16
Corrected apparent limestone neutron porosity, φADNcor (p.u.)
Bulk density,ρb (g/cm3)
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
Fresh Water, Liquid-Filled Borehole (ρf = 1.0 g/cm3)
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
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219
Por
GeneralPorosity—LWD
PurposeThis chart is used similarly to Chart Por-15 to determine the lithologyand crossplot porosity from adnVISION825 8.25-in. Azimuthal DensityNeutron values.
adnVISION825* 8.25-in. Azimuthal Density Neutron ToolPorosity and Lithology—Open Hole Por-17
Corrected apparent limestone neutron porosity, φADNcor (p.u.)
Bulk density,ρb (g/cm3)
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
Fresh Water, Liquid-Filled Borehole (ρf = 1.0 g/cm3)
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
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220
Por
GeneralPorosity—Wireline
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.
Find: Crossplot porosity and lithology.
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
Time averageField observation
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
*Mark of Schlumberger© Schlumberger
222
Por
GeneralPorosity—Wireline
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
Time averageField observation
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.
*Mark of Schlumberger© Schlumberger
continued on next page
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.
Find: Crossplot porosity and lithology.
Answer: Limestone with a crossplot porosity = 24 p.u.
224
Por
GeneralPorosity—Wireline, LWD
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)
Bulk density,ρb (g/cm3)
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
Time averageField observation
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.
GeneralPorosity—Wireline, LWD
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)
Bulk density,ρb (g/cm3)
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
Time averageField observation
30
10
Quartz
sand
stone
20
20
40
© Schlumberger
226
Por
GeneralPorosity—Wireline, LWD
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
*Mark of Schlumberger© Schlumberger
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.)
*Mark of Schlumberger© Schlumberger
232
Por
GeneralPorosity—Wireline
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
*Mark of Schlumberger© Schlumberger
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.