03-maturity-expulsion.pdf

SOME QUESTIONS REGARDING SOURCE ROCK: 1. Does the sediment have enough organic materials? (richness) 2. Is the organic materials appropriate? (type) 3. Has the organic materials been mature? (maturity) 4. Has the hydrocarbon been expelled? (expulsion)

Maturity based on Rock-Eval™

Pyrolysis Tmax: Immature < 435oC Early mature: 435-445oC Peak mature: 445-450oC Late mature: 450-470oC Postmature > 470oC Waples (1985)

Foster and Beaumont (1991)

Bordenave (1993)

Maturity based on vitrinite reflectance

Vitrinite reflectance as a tool to assess thermal maturity (Senftle and Landis, 1991)  Thermal evolution (maturation) of kerogen is chemically and physically similar to coalification.  When progressively buried under sedimentary deposits, peat undergoes chemical and physical changes passing from lignite to bituminous coal, then to anthracite.

Courtesy of USGS

Buehler Ecomet 4 variable speed grinder-polisher

Courtesy of USGS

Leitz orthoplan microscope

Zeiss AxioImager

Courtesy of USGS

QDI CoalPro™ Vitrinite Reflectance Measurement System

Shaly coal from the Upper Triassic containing abundant thick-walled cutinite and vitrinite formed from leaf tissue. The cutinite shows variable fluorescence intensity and colour.

Vitrinite of metaanthracitic rank from pre-Tertiary basement in western Indonesia. The vitrinite is parallel with the polars and is showing the maximum reflectance of 8.05%. The high bireflectance is characteristic of regionally metamorphic effects.

Courtesy of USGS

Photomicrograph of low volatile bituminous coal from West Virginia with a mean maximum reflectance of 0.879%. The maceral shown is vitrinite.

Courtesy of USGS

Vitrinite showing fluorescence from cell walls. 1. T5809; Hole 1109D; 387.86 mbsf. Longitudinal section of wood preserved as telovitrinite. The cell lumens are mostly filled with humic material, but the degree of compressions is small and some parts of the lumens are open. Cell walls are much lower in reflectance and are strongly fluorescing. Their reflectances are within the range normally associated with liptinite, but they do not represent suberinite. Reflectances of the cell walls are lower in the lower part of the field, but the cell contents have relatively consistent reflectances across the various tissue types (reflected light; field width = 0.22 mm; vitrinite reflectance [cell contents] = 0.37%, [cell walls] = 0.12%).

 Coal petrographers have used VR to study coalification in detail for many decades.  Coal rank is determined by the mean maximum reflectance of vitrinite.  VR has been successfully demonstrated as a reliable indicator of organic maturation in sedimentary rocks (Castano and Sparks, 1974).  Early work, VR is suggested being a maturity measurement independent of kerogen composition, organic facies, and depositional processes (Stach et al., 1982).  More recent work has shown that this is not always correct  vitrinite is identified cautiously in shales and other clastic sedimentary rocks (Jones and Edison, 1979; Bostick, 1979; Price and Barker, 1985).

Company Well Sample Type

: : :

KNOC Wulan-1 ST geochem can sample

TABL E-4 VI TRI NI TE REFL ECTANCE RESUL TS Sample depth (m)

Plug Type

M ean Ro (% )

No. of Readings

M inimum Reflectance M aximum Reflectance (% ) (% )

SD

1 1720.0 - 1770.0

C

0.37

2

0.28

0.46

0.090

2 1770.0 - 1820.0

C

0.39

16

0.33

0.45

0.036

3 1820.0 - 1870.0

C

0.46

18

0.39

0.50

0.037

4 1920.0 - 1970.0

C

0.45

17

0.39

0.56

0.043

5 1970.0 - 2020.0

C

0.43

16

0.40

0.52

0.039

6 2020.0 - 2070.0

C

0.51

13

0.41

0.63

0.059

7 2070.0 - 2120.0

C

0.43

16

0.40

0.49

0.029

8 2120.0 - 2170.0

C

0.49

12

0.40

0.58

0.064

9 2170.0 - 2220.0

C

0.49

19

0.41

0.61

0.052

10 2220.0 - 2270.0

C

0.55

14

0.43

0.63

0.051

11 2270.0 - 2320.0

C

0.55

18

0.46

0.68

0.075

12 2320.0 - 2370.0

C

0.50

9

0.46

0.63

0.051

13 2370.0 - 2420.0

C

0.50

11

0.45

0.61

0.041

14 2420.0 - 2470.0

C

0.70

14

0.63

0.78

0.058

15 2520.0 - 2570.0

C

0.77

(1.16)

5

(7)

0.70 (1.01)

0.88 (1.40)

0.081 (0.152)

16 2570.0 - 2620.0

C

0.62

(3.08)

7

(14)

0.50 (2.59)

0.72 (4.19)

0.066 (0.431)

17 2620.0 - 2670.0

C

(12)

(2.28)

(3.86)

(0.439)

C = Kerogen Concentrate

(3.02)

SD = Standard Deviation ( ) = Oxidised population possibly reworked

Company Well Sample Type

: KNOC : Wulan-1 ST : Kerogen Concentrate

Appendix 1. VI TRI NI TE REFL ECTANCE RAW DATA Sample depth (m)

Vro % reading

1720 - 1770.0

0.28 0.46

1770 - 1820.0

0.33 0.33 0.35 0.35 0.38 0.38 0.38 0.38 0.38 0.38 0.39 0.39 0.43 0.43 0.45 0.45

1820 - 1870.0

0.39 0.39 0.41 0.41 0.45 0.45 0.48 0.48 0.48 0.48 0.49 0.49 0.49 0.49 0.49 0.49 0.50 0.50

1920 - 1970.0

0.39 0.39 0.40 0.42 0.42 0.43 0.43 0.43 0.43 0.43 0.48 0.48 0.48 0.48 0.48 0.49 0.56

1970 - 2020.0

0.40 0.40 0.40 0.40 0.40 0.40 0.41 0.41 0.41 0.41 0.42 0.42 0.45 0.45 0.52 0.52

2020 - 2070.0

0.41 0.44 0.46 0.48 0.48 0.49 0.51 0.52 0.53 0.53 0.54 0.61 0.63

2070 - 2120.0

0.40 0.40 0.40 0.40 0.41 0.41 0.41 0.41 0.42 0.42 0.44 0.44 0.45 0.45 0.49 0.49

2120 - 2170.0

0.40 0.40 0.40 0.43 0.49 0.51 0.52 0.53 0.53 0.55 0.56 0.58

2170 - 2220.0

0.41 0.42 0.43 0.43 0.44 0.45 0.47 0.47 0.48 0.49 0.50 0.51 0.52 0.52 0.53 0.54 0.54 0.56 0.61

2220 - 2270.0

0.43 0.48 0.50 0.52 0.54 0.55 0.55 0.56 0.56 0.57 0.59 0.59 0.61 0.63

2270 - 2320.0

0.46 0.46 0.46 0.46 0.50 0.50 0.50 0.50 0.56 0.56 0.59 0.59 0.60 0.60 0.64 0.64 0.68 0.68

2320 - 2370.0

0.46 0.46 0.46 0.48 0.48 0.48 0.49 0.53 0.63

2370 - 2420.0

0.45 0.46 0.48 0.49 0.49 0.50 0.50 0.50 0.52 0.54 0.61

2420 - 2470.0

0.63 0.63 0.63 0.63 0.65 0.65 0.71 0.71 0.73 0.73 0.76 0.76 0.78 0.78

2520 - 2570.0

0.70 0.70 0.70 0.85 0.88

2570 - 2620.0

0.50 0.58 0.60 0.61 0.66 0.67 0.72

2620 - 2670.0

Semi-logarithmic Depth (m) 1500

3000

4500

6000 0.2

0.4 0.6 0.8 1.0 2.0 3.0 Vitrinite reflectance (%)

LINEAR Depth (m) 1500

3000

4500

6000 0.2

0.4

0.6 0.8 1.0 1.2 1.4 Vitrinite reflectance (%)

1.6

 Among the optical properties used to characterize OM, VR is the most common property measured.  VR is the proportion of normally incident light reflected by a plane and polished surface of the substance under consideration.  VR is expressed as a percentage of the light incident on the surface.  Only the amount of light reflected in the green visible wave-lengths (546 nm) is measured.  The amount of reflected light is a small fraction, generally less than 4%.

VR is done on the vitrinite macerals for at least three reasons:  Vitrinite is the predominant maceral.  Individual vitrinite often appears homogeneous.  The particle size is large enough to permit measurements.

 As with coals, vitrinite in fine-grained clastic rocks often appears homogeneous and is sufficiently large to permit measurement.  VR offers a means to evaluate organic maturity over temperatures ranging from early diagenesis through catagenesis to metamorphism (next figure).

After Sentfle and Landis, 1991

VITRINITE REFLECTANCE <0.5 – 0.7%

diagenesis

0.7 – 1.3%

catagenesis (oil window)

1.3 – 2.0%

late catagenesis or primary gas zone

>2%

metagenesis (dry gas)

DISADVANTAGES OF THE VR METHOD 1. Vitrinite is difficult to be found in types I and II kerogens. 2. Transformation rate may be different among kerogens although their maturity level is similar. 3. Failure in maceral identification. 4. Source rocks older than Silurian do not contain vitrinite.

 VR can be measured either in a whole rock or in an isolated kerogen samples.  The advantage using the whole rock is the clarity of the VR measurement (primary versus reworked vitrinites).  The disadvantage is the number of vitrinite in whole rock is usually limited, since the percentage of vitrinite is often less than 5%.  Jones and Edison (1979) note that in many samples, not enough individual measurements are available to calculate a statistically significant average.

 Generally, 20 measurements are needed to evaluate a sample.  Concentrated kerogen preparations are widely used within the petroleum industry.  This permits the acquisition of a large number of measurements (50-100 readings) from humic OM.  A range of reflectance histograms may be encountered in well section (see the next figure).

 Most reflectance histograms represent multiple populations of vitrinite due to incorporation of caved overlying rocks during drilling, vitrinite and inertinite identificationproblems and reworked vitrinites of higher reflectance deposited into the sedimentary section.  Identification of indigenous vitrinite population can be assisted through study of samples from the well taken above and below the sample interval and the comparison with additional maturity indicators.

 Coal seams within well sections serve as reference points in maturity profiles  abundant and, in most cases, forms in situ.  The vitrinite population in coals is relatively less complicated compared with clastic rocks.  If dealing with ditch cuttings, care must be taken to sample indigenous lithologies  coals are prone to cave and washout.

 VR profiles can contribute to studies of common geological problems.  Common VR profiles encountered from thick sections reflect a range of basin-scale geological processes (see the next figure).  Case study-2

After Sentfle and Landis (1991)

Unconformity

Normal and thrust faults

Overpressure

Up-lifting

Change of heat-flow

Intrusion

Cooper (1990)

NEGATIVE ANOMALY (SUPPRESSION) (next figure)  Many studies have linked anomalously low VR values to significant concentrations of exinite, including amorphous organic matter in coals and rocks (Sentfle and Landis, 1991 and references therein).  Other studies indicate that anomalous VR data may relate to depositional environment, plant communities, and hydrogen-enriched “saprovitrinites” in some coals and shales.  Low-reflecting, hydrogen-enriched vitrinites are common in type I and type II kerogens. Enrichment happens during deposition in anoxic environments and early diagenesis.  Vitrinite is impregnated by bitumen or mobile hydrocarbons.

Correlation table of common organic maturation parameters with coal rank and hydrocarbon generation (Sanftle and Landis, 1991).

SOME QUESTIONS REGARDING SOURCE ROCK: 1. Does the sediment have enough organic materials? (richness) 2. Is the organic materials appropriate? (type) 3. Has the organic materials been mature? (maturity) 4. Has the hydrocarbon been expelled? (expulsion)

Migration “in”

Migration “out”

Tissot and Welte (1985)

VITRINITE REFLECTION CORRECTION (Lo, 1993) Case study-3 (in the end of this session)

 Suppressed VR is mainly due to the difficulties faced by organic petrographers to find vitrinite particles in a kerogen whose hydrogen content is high.  The next figure shows how to make a correction based on diagram proposed by Lo (1993).

Measured Vitrinite Reflectance (%Ro)

2

HIo < 100 HIo = 300

1.5 HIo = 600 HIo = 900

1

0.5

0.5

1

1.5

Maximum True Vitrinite Reflectance (%Ro) A proposed VR correction model by Lo (1993).

2

 Initial hydrogen index is needed in the modelling process.  HIo is HI when the sample (sediment) is still immature.  HIo value decreases with increasing maturity.

Initial hydrogen index (HIo) can be: • assumed based on pyrolysis data for similar and same level sample that is immature. • backtrack from measured HI and Tmax (be careful!) • HIo can be assumed from organic petrology data: 0 – 50 for inertinite 100 – 200 for vitrinite 400 – 600 for exinite 600 – 800 for alginite

Jarvie et al. (2007) HIo value can be computed from visual kerogen assessments and assigned kerogen-type HIo average values using the following equation: % type I % type II % type III % type IV HIo = ----------- x 750 + ------------ x 450 + ------------- x 125 + ------------- x 50 100 100 100 100

This equation requires input of maceral percentages from visual kerogen assessment of a source rock. For example: using certain shale that is 95% type II and 5% type III, the calculated HIo would be 434 mg HC/g TOC. At 100% type II, HIo would be 450 mg HC/g TOC.

AAPG Bulletin vol. 91, April 2007

Vitrinite suppression (Lo, 1993)

• An example of VR suppression in Williston Basin (Price dan Barker, 1985). • VR suppression in the Bakken Shale is given in the next figure. • It seems that VR suppression in the Bakken Shale is too high compared with the regional VR trend. • Suppressed to 0.8% from the regional assumption of 2.2%.

Depth (1000 feet)

0

Middle Jurassic - Tertiary 5 Devonian – Early Jurassic

? 10

?

Bakken Shale

?

15 0.2

0.3

0.5

1.0

2.0

3.0

Vitrinite Reflectance (%Ro) An example of VR suppression in a well-profile (from Price and Barker, 1985).

Vitrinite suppression (Lo, 1993)

• Hydrogen index (HI) of coals influence their VR suppression. • The next figure shows VR coals collected with a depth interval of 70 meters. • VR seems to decrease with the increasing of HI (Bostick, 1986)

• Data from a 70 m of Pa coal seam (Bostick, 1986) • These coals should have the same maturity (Ro) • Hydrogen index (HI) is a factor affecting Ro

An example of VR suppression in coals (from Lo, 1993).

Vitrinite suppression (Lo, 1993)

• Comparison in measuring reflectance on vitrinite and sporinite (next figure).

Table 1. Data showing a correlation among hydrogen index (HI), vitrinite reflectance (Ro), and equivalent vitrinite reflectance (EqVR).

No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Well Name BW-1 PD-1 PD-1 LH-1 LH-1 BW-1 BW-1 LH-1 SB-43 BW-1 PD-1 PD-1 PD-1 BW-1 BW-1 PG-54 PG-54 PG-54 PG-54 PG-54 PG-54 PG-54 PG-54 PG-54

Depth (ft) 3870 3410 3728 7950 4450 3673 3733 6850 4100 3622 3150 3100 3620 3642 3575 4874 4846 4886 4852 4840 4327 4870 3997 4127

Sedimentary Basin C. Sumatra C. Sumatra C. Sumatra Kutai Kutai C. Sumatra C. Sumatra Kutai Kutai C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra C. Sumatra

HI 0 0 34 64 89 103 107 107 116 119 182 190 200 272 353 413 467 467 476 480 513 544 590 628

Ro (%) 0.63 0.51 0.61 0.6 0.51 0.58 0.59 0.51 0.48 0.61 0.51 0.47 0.53 0.54 0.44 0.56 0.57 0.59 0.61 0.62 0.51 0.56 0.46 0.47

EqVR 0.72 0.57 0.64 0.6 0.51 0.73 0.72 0.57 0.48 0.7 0.64 0.59 0.65 0.71 0.77 0.1.1 1.05 1.13 1.15 1.12 1.08 1.13 0.98 0.97

A proposed model for the suppression of vitrinite reflectance 0.8

Measured Ro

0.7

0.6

0.5

0.4 0.3 0.2 0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

Corrected Ro HI < 150 (Sumteng) HI < 150 (Kutai)

HI 150-300 (Sumteng) HI 150-300 (Kutai)

Linear (HI > 500 (Sumteng))

Linear (HI < 150 (Sumteng))

HI 300-500 (Sumteng) Linear (HI 150-300 (Sumteng))

HI > 500 (Sumteng) Linear (HI 300-500 (Sumteng))

Table 2. Data of Measured, Corrected Vitrinite Reflectance, and EqVR Depth No (feet) Well: BW-1 1 3575 2 3622 3 3642 3673 4 5 3733 6 3870 Well: PD-1 1 3100 2 3150 3 3410 4 3620 5 3728 Well: PG-54 1 3997 2 4127 3 4327 4 4840 5 4846 6 4852 7 4870 8 4874 9 4886

HI

Measured VR

Corrected VR

EqVR

353 119 272 103 107 0

0.44 0.61 0.54 0.58 0.59 0.63

0.77 0.71 0.71 0.68 0.7 0.76

0.77 0.7 0.71 0.73 0.72 0.72

190 182 0 200 34

0.47 0.51 0.51 0.53 0.61

0.58 0.64 0.51 0.67 0.71

0.59 0.64 0.57 0.65 0.64

590 628 513 480 467 476 544 413 467

0.46 0.47 0.51 0.62 0.57 0.61 0.56 0.56 0.59

0.97 0.97 1.05 1.16 1.06 1.14 1.13 1.04 1.12

0.98 0.97 1.08 1.12 1.05 1.15 1.13 1.04 1.13

VITRINITE REFLECTION CORRECTION USING FAMM (FLUORESCENCE ALTERATION OF MULTIPLE MACERALS) TECHNIQUE Case study-3

SAMPLE

EqVR DATA

VR DATA

Depth (m/ft)

CSIRO Sample No.

Formation

EqVR (%)

Range (%)

Suppression

Rmo

Range (%)

n

s

1750.2/5 742

55833

Brown Shale

0.64

0.53-0.77

Minimalmoderate

0.49

0.40- 0.62

25

0.06

1750.8/5 744

55834

Brown Shale

0.63

0.56-0.67

Minimal

0.59

0.48- 0.64

25

0.04

1755.3/5 759

55835

Brown Shale

0.60

0.53-0.70

Minimal

0.62

0.51- 0.69

25

0.05

1756.6/5 763

55836

Brown Shale

0.66

0.56-0.74

Minimal

0.50

0.32- 0.62

21

0.08

1760.2/5 775

55837

Brown Shale

0.72

0.62-0.77

Moderate

0.50

0.41- 0.65

28

0.06

1764.5/5 789

55838

Brown Shale

n.a

-

-

0.32

0.28- 0.36

3

0.04

1765.4/5 792

55839

Brown Shale

~0.74

-

Severe

0.42

0.35- 0.49

2

0.10

1766.0/5 794

55840

Brown Shale

0.73

0.66-0.86

Moderate

0.44

0.38- 0.53

26

0.04

1776.7/5 829

55841

Brown Shale

n.a

-

-

n/a

-

-

1807.2/5 929

55842

n.a

-

-

0.60

4

0.02

1 VR

0.58- 0.62

N.a. = Not available due to a lack of indigenous organic matter EqVR = FAMM-derived equivalent vitrinite reflectance calibrated against Rmo%. Rmo% = Mean vitrinite reflectance measured under oil immersion on randomly oriented phytoclasts in nonpolarised light. n = Number of vitrinite reflectance readings; σ = standard deviation. Readings taken from dispersed organic matter (DOM) and coal. The ranges in EqVR are based on plotted positions of vitrinite data in relation to iso-EqVR lines on the FAMM diagrams 1

The degree of vitrinite reflectance suppression/enhancement is based on the position of the vitrinite data points in relation to iso-correction curves superimposed on the fluorescence alteration diagram; minimal (0.00.1%), moderate (>0.1-0.2%) and severe (>0.2%); enhancement shown in parentheses