Fluid Identification Using Neutron

Porosity and Bulk Density Logs

Neutron and Density Logs on Compatible Scales

• The neutron porosity and bulk density logs are used to identify reservoir fluid type in addition to computing the formation porosity, shale volume, etc.

• In order to correctly identify the reservoir fluid type, the neutron porosity and bulk density logs must be plotted and displayed on what is known as compatible scales.

• As an industry standard the Neutron Porosity log is recorded in Limestone Porosity Units and displayed in either V/V units, P.U. (Porosity Units), % (percentage) or decimal units (dec.).

• The Bulk Density log is displayed in gm/cc (oilfield units) or kg/m3 (kg/cubic meter) in SI units.

• The neutron porosity logging tool is calibrated in limestone porosity units and the bulk density logging tool is calibrated in density units.

• The following slides explain about how the neutron porosity and density logs should be plotted and displayed on compatible scales to facilitate in identification of reservoir fluid type.

Thermal Neutron Porosity Equivalence Curves

The porosity equivalence curve for Limestone is a straight line.

It has a one-to-one relationship, between the apparent measured

limestone porosity and the true porosity for the indicated matrix.

The equivalence curves for Sandstone and Dolomite have non-

linear relationships. They are curved lines.

Courtesy of Schlumberger

Matrix point for limestone: RHOB = 2.71 gm/cc and NPHI = 0 P.U.Matrix point for sandstone: RHOB = 2.65 gm/cc and NPHI = -3 P.U.

Courtesy of Schlumberger

Courtesy of Schlumberger

Tight Rocks

Location of Neutron Porosity and Bulk Density data points

Gas: Low Density, Low Neutron porosity - North West quadrant

Tight Rocks: High Density, Low Neutron porosity - South West quadrant

Shales: High Density, High Neutron porosity – South East quadrant

Coals: Low Density, High Neutron porosity – North East quadrant

Bad Hole: Low density, High Neutron porosity – North East quadrant

Sandstone compatible scales

Note: When RHOB = 2.65 gm/cc, NPHI = -3 P.U.

NPHI must be in Limestone Porosity Units.

Note: When RHOB = 2.71 gm/cc, NPHI = 0 P.U.

NPHI must be in Limestone Porosity Units.

Courtesy of Baker Hughes

Shifting of logs by changing presentation scales can result

in the separation between neutron and density logs to be

increased, reduced or totally disappear depending on how

the scales are changed

Gas bearing sandstone reservoir

Neutron and Density logs plotted on sandstone compatible scale.

FDC and CNL are trademarks of Schlumberger

FDC: Formation Density Compensated log (Bulk density log)

CNL: Compensated Neutron Log (Neutron porosity log)

Gas Bearing Sandstone

Gas

Oil Bearing Sandstone

Water Bearing Shaly Sandstone

COAL

Coal Beds

CARBONACEAOUS

SHALE

COAL

Carbonaceous Shale

Gas Bearing Limestone

Gas

Water Bearing Limestone

Dolomitic Limestone

Ha Long-1X

TNPH / RHOZ

Interval : 1675. : 1905.

3.

2.8

2.6

2.4

2.2

2.

RH

OZ

-0.05 0.07 0.19 0.31 0.43 0.55

TNPH

0.

15.

30.

45.

60.

75.

90.

105.

120.

135.

150.

DSOZ

SS 0

10

20

30

40

LS 0

10

20

30

40

DOL 0

10

20

30

40

(SWS) Density Neutron(NPHI) Overlay, Rhofluid = 1.0 (CP-1c 1989)

1510 points plotted out of 1510

Well Depths

Ha Long-1X 1675.M - 1905.M

Tight Carbonate Reservoir

Jacaranda-1

NPHI / RHOB

Interval : 1490. : 1650.

3.

2.8

2.6

2.4

2.2

2.

RH

OB

-0.05 0.05 0.15 0.25 0.35 0.45

NPHI

0.

15.

30.

45.

60.

75.

90.

105.

120.

135.

150.

GR

SS 0

10

20

30

40

LS 0

10

20

30

40

DOL 0

10

20

30

40

(SWS) Density Neutron(NPHI) Overlay, Rhofluid = 1.0 (CP-1c 1989)

1014 points plotted out of 1051

Well Depths

Jacaranda-1 1490.M - 1650.M

Basalt Beds

Jade-2X

TNPH / RHOZ

Interval : 2960. : 3220.

3.

2.8

2.6

2.4

2.2

2.

RH

OZ

-0.05 0.05 0.15 0.25 0.35 0.45

TNPH

50.

70.

90.

110.

130.

150.

170.

190.

210.

230.

250.

ECGR

SS 0

10

20

30

40

LS 0

10

20

30

40

DOL 0

10

20

30

40

(SWS) Density Neutron(NPHI) Overlay, Rhofluid = 1.0 (CP-1c 1989)

1519 points plotted out of 1707

Well Depths

Jade-2X 2960.M - 3220.M

Intrusive Volcanic Bed

Kamia-1

CN / ZDEN

Interval : 1130. : 1215.

3.

2.8

2.6

2.4

2.2

2.

ZD

EN

-0.05 0.05 0.15 0.25 0.35 0.45

CN

0.

15.

30.

45.

60.

75.

90.

105.

120.

135.

150.

GR

SS 0

10

20

30

40

LS 0

10

20

30

40

DOL 0

10

20

30

40

(WA) Neutron Density Overlay, Rhofluid = 1.0 (Ch.6-42 1985)

674 points plotted out of 1117

Well Depths

Kamia-1 1130.M - 1215.M

Conglomerate Bed

Courtesy of Schlumberger

The End