Crossplots for Porosity, Lithology and Saturation

4-1

CP

The neutron-density-sonic crossplot charts (Charts CP-1, CP-2and CP-7) provide insight into lithology and permit the determi-nation of porosity. Chart selection depends on the anticipatedmineralogy. Neutron-density can be used to differentiate betweenthe common reservoir rocks [quartz sandstone, calcite (lime-stone) and dolomite] and shale and some evaporites.

Sonic-neutron can be used to differentiate between the commonreservoir rocks when clay content is negligible. Sonic-densitycan be used to differentiate between a single known reservoirrock and shale and to identify evaporate minerals.

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Porosity and Lithology Determination fromFormation Density Log and SNP Sidewall Neutron Porosity Log CP-1a

0 10 20 30 40

φSNPcor, neutron porosity index (p.u.) (apparent limestone porosity)

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

ρ b, b

ulk

dens

ity (

g/cm

3 )

φ D, d

ensi

ty p

oros

ity (

p.u.

) (ρ

ma

= 2

.71,

ρf =

1.0

)

45

40

35

30

25

20

15

10

5

0

–5

–10

–15

Sulfur Salt

Trona

Polyhalite

Langbeinite

Approximategascorrection

Anhyd

rite

0

Dolomite

0

5

10

15

20

25

30

35

Quartz sa

ndstone

Porosity

0

5

10

15

20

25

30

35

40

Calcite (li

mestone)

0

5

10

15

20

25

30

35

40

45

Fresh water, liquid-filled holes (ρf = 1.0)

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