Physics and Biology of

Biogenic Gas Plays:

Implications for South-

East Asia

Duncan Macgregor

Order of Presentation

Biogenic Gas Distribution and

Models

SE Asia PVT Studies

Screening Criteria

Conclusions

Global and SEA Biogenic Gas Reserves

Terang/Sirasun

Shwe

Sebei

Isotopic Composition

Biogenic Gas

δC13 C1<-600/00

CGR ~0

Sebei

Shwe

Terang-Sirasun

Cumulative Discovery Curve : Global

Biogenic Gas Reserves (excluding West Siberia)

Trinidad, Guajira

Terang-Sirasun NileLevantine s/water

Sebei

Levantine and Eratosthenesd/water

Shwe

Po, Stavropol, Cook Inlet

Shallow water Deep water

Summary of Methanogen Activity Models

Re

lati

ve

Bio

ge

nic

Ga

s P

rod

uc

tiv

ity

Temperature

800c500c400c 600c300c200c 700c

Katz 2011

Pang et al 2005(Qaidam)

Pujol et al, 2016

Odedra et al 2005

Peak of Mesophiles

Peak of Thermophiles

Hyperthermophiles

Reservoir Temperature of Biogenic

Gas Reservoirs

Zawtika

Shwe

Sebei, Terang-Sirasun

SE Asia Gas ColumnsG

AS C

OLU

MN

(m

)

OVERBURDEN (m)500

1000

1500 2500 35001000 2000 3000 4000

200

400

600

800

1200

1400

1600

1800

Biogenic/Mixed Gas – non-spillfull

Biogenic/Mixed Gas –spillfull

Thermogenic Gas – non-spillfull

Thermogenic Gas – spillfull

Carbon Dioxide

SHWE

TERANG

?

Pandora

Zawtika

Biogenic Gas Habitats

DEP

TH,

TEM

PER

ATU

RE, P

RESSU

RE,

CO

MP

AC

TIO

N, S

EA

L C

AP

AC

ITY

VO

LUM

E

MESOPHILE PEAK ~40oC

THERMOPHILE PEAK ~65oC

HYPERTHERMOPHILES >70oC

GAS HYDRATES <19oC

FREE BIOGENIC

GAS (<90oC)

DISSOLVED

AND

ADSORBED

GAS (coal;

bed

methane)

ORGANIC RICH SILTS AND MUDS

+ COALS

GAS

SATURATED

SILTS AND

MUDS (shale

gas)

?

?

Uplift/Degassing

Compaction

OIL (secondary

Biogenic Gas)

Seepage

Leakage

Order of Presentation

Biogenic Gas Distribution and

Models

SE Asia PVT Studies

Screening Criteria

Conclusions

Temperature-Overburden-

Gas Expansion Factor

Relationships : Shallow Water

Setting

Bg = V surface/V subsurface

Ove

rbu

rde

n (

m)

40oC

70oCBoyles Law (ideal gas)

𝑃1𝑉1𝑇1

=𝑃2𝑉2𝑇2

Amended for non-ideal

gas (methane) by

compressibility factor z

significant shrinkage

within biogenic window

SEA

L C

AP

AC

ITY

Sebei PVT History

32oC/Ma

RESERVOIR

TRAP

SEALSEAL

DYNAMIC

BIOGENI

C

CHARGE

Uplift and water influx

Terang-Sirasun PVT History

90oC/Ma

RESERVOIR

SEAL

BIOGENIC PEAKBIOGENIC PEAK

SEAL

TRAP TRAP

TRAP BREACH

Zawtika PVT History

27oC/Ma

HYDRATES

RESERVOIR

TRAP

SEAL

BIOGENIC PEAK

BIOGENIC LIMIT

Temperature-Overburden-

Gas Expansion Factor

Relationships : Deep Water

Setting

Bg = V surface/V subsurface

Ove

rbu

rde

n (

m) 40oC

70oC

19oC Gas Hydrate Base

Boyles Law (ideal gas)

𝑃1𝑉1𝑇1

=𝑃2𝑉2𝑇2

Amended for non-ideal

gas (methane) by

compressibility factor z

minimal shrinkage

within biogenic window

SEA

L C

AP

AC

ITY

Shwe PVT History

17oC/Ma

HYDRATES

RESERVOIR

TRAP

SEAL

BIOGENIC PEAK

BIOGENIC LIMIT

compaction of paleo-hydrates?

Order of Presentation

Biogenic Gas Distribution and

Models

SE Asia PVT Studies

Screening Criteria

Conclusions

Key Factors for Biogenic Gas

Type iii kerogen supply, often a delta/prodelta

TOC >0.3% but hundreds/kilometres thick

Anoxia and/or Rapid Deposition

Burial rates between 200-1000m/Ma (5-25 deg C/km)

Undercompacted Sediments – 2µm pore spaces NOT SHALES

Low Temperatures / Geothermal Gradient

Ideally low surface temperature (deep water)

Typically below 25 degC/km

Highly pressured deep marine setting during deposition

Reduces potential for shrinkage on leaving biogenic window

Early Trap and Seal Formation

Trap in place and seal compacted while in main stages of biogenic window

Syn-sedimentary structural traps

Carbonate Buildups

TRAPPING AND

PRESERVATION

PVT

CONDI

TIONS

FEEDSTOCK

Rice, 1989

Biogenic Gas Basin Screening

Matrix

Biogenic Screening : Organic

Feedstock- Present Day TOC

0.25%

2%

1%

Acknowledgement : P and J. Allen and John Wiley & Sons

for making this figure from their book ‘Basin Analysis :

Principles and Application to Petroleum Play Assessment’

available for educational purposes on the internet

Biogenic Screening : Gas

Hydrates/Bottom Simulating Reflectors

Deep Gulf of Martaban, Wang 2011

Known Hydrates and BSRs

Largely after Prabhakar 2012 and

Lorenson and Kvenvolden 2010

Biogenic Screening : Geothermal

Gradients below 25oC/km

Based on RHUL thermal database

Biogenic Screening : Timing of Trap Formation

Sapiie et al 2012/TGS

Conclusions

Biogenic Gas may be an underestimated resource in SE Asia

The potential in deep water is greater than that onshore or on the

shelf (cold seabed, seal capacity, gas hydrates, high pressures)

Significant resources of biogenic gas can lie below the active

biogenic generation window

Screening for biogenic gas should be run independently for that for

thermogenic petroleum as success factors are different and

sometimes exclusive. These include

Very early trap formation, e.g. carbonate buildups and syn-

sedimentary anticlines

Low thermal gradient – favours e.g. east Indonesian basins

Presence of bottom simulating reflectors = gas hydrates

High depositional rates and undercompacted sediments