FORMATION EVALUATION

PETE 321

Summer 2010

CROSSPLOTS(Porosity and Lithology)

TWO-MEASUREMENT POROSITY CROSSPLOTS

• Two measurements determine two unknowns– Formations with one lithology

• Lithology• Porosity

– Formations of two known constituents• Can determine a more accurate value of porosity• Can determine the percentage of each mineral

– Complex lithologies• Can determine a more accurate value of porosity• Cannot determine percentage mineral makeup

COMMON POROSITY CROSSPLOTS

• Neutron-density

• Sonic-neutron

• Sonic-density

• All have complicating effects– Shaliness– Hydrocarbons (gas)– Fractures

NEUTRON-DENSITY CROSSPLOTS

• Most frequently used

• Developed for clean, liquid-saturatedformations

• Boreholes filled with water or water-based muds

• Several charts, depending on tools– CP-1’s Schlumberger– CNT-K-1’s and DSN-II-1’s Halliburton

• Axes– Neutron limestone– Density

• NE-SW Lith. Lines– Sandstone– Limestone– Dolomite

NEUTRON DENSITY

CROSSPLOT

• NW-SE Por. Lines– Connect equal por pts– Nearly parallel

φ = 20

SulfurSalt

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Trona

PolyhaliteLangbeiniteBul

k de

nsity

(Mm

g/m

3or

g/c

c)

403020100Apparent neutron porosity (lspu)

φ = 10

φ = 30

22%

2.45

A

B

C

% Ls = BC / AC% Dol = AB / AC

Matrix may be:• Ls and dolomite• Ss and dolomite

~2.83

SulfurSalt

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Trona

PolyhaliteLangbeiniteBul

k de

nsity

(Mg/

m3

or g

/cc)

403020100Apparent neutron porosity (lspu)

CHART BASED on...– POR-12/13 Neutron

– POR-10 Density

SulfurSalt

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Trona

PolyhaliteLangbeiniteBul

k de

nsity

(Mg/

m3

or g

/cc)

403020100Apparent neutron porosity (lspu)

• Parallel lith. lines– Constant separation– Distinct position

• Log presentation(next)

• Parallel lith. lines– Constant separation– Distinct position– Log presentation

• Limestone scaling– Neutron 45 to -15 lspu– Density 1.95 to 2.95 g/cc– LS ρ and φ values overlie

in Ls

• Other scalings possible

|2.7

0|DENSITY-NEUTRON

PRESENTATION

φ=12 ss ρb =2.45; φn = 9

φ=30 ss ρb =2.15; φn = 27

φ=12 dol ρb =2.67; φn = 15

φ=30 dol ρb =2.33; φn = 33

φ=12 ls

ρb ~2.53φ=30 ls ρb ~2.23

EXAMPLE LOG - WELL “X”• 90-260ft Zone D

– OWC @ 150ft– Pe = 1.8 - 2: SS– Den-Neut

• LS compatible• Ntrn to rt of Den• SS lithology• Large sep. above

150 ft

• Shales– Pe = 2.5 - 3– Neutron left of

Density

B

C

D

OWC

OTHER EFFECTS

• ShalesSulfur

Salt

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Trona

PolyhaliteLangbeiniteBul

k de

nsity

(Mg/

m3

or g

/cc)

403020100Apparent neutron porosity (lspu)

• Gas

• Fractures– No effect, both

logs respond tototal porosity

EXAMPLE LOG - DN PLOT, WELL “X”

Shale Effect

Borehole effects and calcite stringers cause outliers

WELL “X”DN PLOT(EXCEL)

Density-Neutron Response

1.9

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3-5 0 5 10 15 20 25 30 35 40 45

Neutron Porosity, limestone

Bul

k de

nsity

, g/c

c

Qtz Calcite DolomiteGR < 30 & ILD < 1 GR > 80 GR < 30 & ILD > 1

Shale plots like dol; use GR to differentiate

Oil

Water

Values do not all fallon Ss line owing to:

• Borehole effects

• Carbonate cements

• Shaliness

• HC vs water

• Statistical fluctuations of tools

GAS EFFECT - 1WELL “A”

• Zone (depth)– A: 0 - 20– B: 20 - 45– C: 45 - 335– D: 335 - 350

• A– Low GR– Den = 2.95 (high)– Neut por. = -2

• B, D – high GR• C

– D-N litho scaling– GWC @ 290 ft.– D-N near overlay

below

A

B

C

D

LS Calibration

GasEffect

0

GAS EFFECT - 2

WELL “A”

AB

D

C

A

D Shale

C

B Marl

DENSITY-NEUTRON - OTHER COMMENTS

• Density log may be displayed as porosity

– Density-Neutron overlay for water- filled lithology

– Curve order as with g/cc scaling

• Shale/Gas effects

– Across litho lines: Lithology most affected

– Along porosity lines: Porosity least affected

• Response lines change with tool type

COMMON POROSITY CROSSPLOTS

• Neutron-density

• Sonic-neutron

• Sonic-density

SONIC-NEUTRON CROSSPLOTS

• Developed for clean, liquid-saturated formations

• Boreholes filled with water or water-base muds

t,So

nic

tran

sit t

ime

(μs/

ft)

110

100

90

80

70

60

50

40403020100

Syivite

Trona

Time average

Field observation

Apparent neutron porosity (lspu)

• Similar layout to density-neutron

• Two lines - two porosity models– Wylie time average– Raymer-Hunt-Gard.

• Charts– CP-2’s (S)– CNT-K-2’s (H)

SONIC-NEUTRON PLOTS - 1

110

100

90

80

70

60

50

40403020100

Syivite

Trona

t,So

nic

tran

sit t

ime

(μs/

ft)

Time averageField observation

Apparent neutron porosity (lspu)

• Shale - NE region

SONIC-NEUTRON PLOTS - 2

• Fracs - South

• Gas - NW

WELL “X,” SN PLOT W/ GR

Sonic-Neutron (CNL), Fresh Mud

40

50

60

70

80

90

100

110

120

-5 0 5 10 15 20 25 30 35 40

Neutron, apparent LS pu

Soni

c sl

owne

ss, m

s/ft

Quartz Calcite Dolomite GR < 30 GR > 80

• Shaliness• Optimistic

porosity• Lithology OK

• HC effect slight

COMMON POROSITY CROSSPLOTS

• Neutron-density

• Sonic-neutron

• Sonic-density• Poor porosity resolution• Useful for some evaporites

SONIC-DENSITY CROSSPLOTS

• Poor lithology and porosity

• Multiple lines– WTA

– RHG

• Useful for– Evaporites– Vsh

Density-Sonic ResponseField Lines Only

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

340 60 80 100

Sonic DT

Den

sity

Qtz Calcite Dolomite

WELL “X,”DENSITY-SONIC

• Clean points cover all lines

• Shale point distinct

Density-Sonic Response

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3

40 60 80 100

Sonic DT

Den

sity

Qtz Calcite Dolomite GR < 30 GR > 90

MID PLOTS - 2 LOGS

DENSITY-SONIC

Vsh

• Locate 100%shaleand cleanformation

• Grid to give Vsh

Density-Sonic Response

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3

40 60 80 100

Sonic DT

Den

sity

Qtz Calcite Dolomite GR < 30 GR > 90

Vsh = 1

Vsh = 0What is shale content of

formation comprisedof 2 minerals?

MID PLOTSPRINCIPLES

• Lith. lines– 3 of many poss.– Each line diff. lith.

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

Bul

k de

nsity

(Mg/

m3

or g

/cc)

403020100Apparent neutron porosity (lspu)

• Line definition– Use endpoint loc’n– Value of ρb for φ = 0– Called ρmaa

ρmaa= 2.68

ρb= 2.30, φn = 21

• ExampleLogs show ρb= 2.30, φn = 21

ρmaa = 2.68

1. DETERMINE APPARENT MATRIX DENSITY

MID PLOTSPRINCIPLES

• Lithology Lines– Similar to D-N

• Line Definition– Use endpoint loc’n– Value of Δt for φ = 0– Called Δtmaa

• ExampleLogs show Δt = 78, φn = 21

Δtmaa = 53

110

100

90

80

70

60

50

40403020100

Syivite

Tronat,

Soni

c tr

ansi

t tim

e (μ

s/ft)

Field observation

Apparent neutron porosity (lspu)

Δt = 78, φn = 21

Δtmaa= 53

2. DETERMINE APPARENT MATRIX TRANSIT TIME

THREE - MEASUREMENT CROSSPLOTS

• For lithology determination only• Used when 3 porosity logs available• Three types

– Density-Neutron-Sonic (M-N plot)– Density-Neutron-Sonic (MID plot)– Density-Neutron-Pe (Umaa -- ρmaa plot)

MID PLOTS PRINCIPLES

• 3 Lithology Points

Results– 50% quartz– 50% calcite

• Exampleρmaa = 2.68Δtmaa = 53 Quartz

Dolomite

Calcite

Δtmaa

Ρ maa

3. DETERMINE LITHOLOGY

Calculating Δtmaa and ρmaa

• At each depth: Δt, ρb, and φn

• 1. Obtain φDN and φSN from crossplots• 2. ρmaa = (ρb − φDNρfl)/(1 - φDN)• 3. Δtmaa = Δt − (φSNΔt)/0.7

– 0.7 factor may vary somewhat

SUMMARY• 3 types of porosity logs

• Density, Neutron, Sonic

• These logs respond differently to matrix, fluids and pore types

• Use for 2-log crossplots

• Crossplots allow determination of porosity and proportions of 2 minerals, if mineralogy is known

• Neutron – density is most commonly used crossplot

SUMMARY

• 3-Log Crossplots– Lithology only– Several versions

• MID plot• MN plot• Umaa -- ρmaa plot