Laboratory experiments at reservoir pressure and temperature of the biogenic methane potential of coal seam reservoirs

CSIRO ENERGY

L.D. Connell , N. Lupton , R. Sander , M. Camilleri, M. Faiz, D. Heryanto, D. Down, D. Midgley, N. Tran-Dinh

12 February 2015

Objectives and Acknowledgments

• Microbially Enhanced Coal Seam Methane (MECSM) project research undertaken jointly with industry.

• Supported and sponsored by Santos Ltd, APLNG, AGL Energy and QGC

• Objective to improve recovery from CSG fields by enhancing the biogenic process

• The Sponsors and CSIRO have agreed to collaborate recognizing the mutual benefit of combining their expertise and resources to conduct the research in pursuit of the Objective

• Phase 1 successfully investigated the potential for microbial enhancement of coal seam gas production from key Australian basins

• Phase 2 is underway. Methane has been successfully generated from core flooding. Current work is focused on upscaling and modelling for potential field trial phase

• This presentation is on the core flooding which formed a component of the program of work under MECSM phase 2

Luke Connell

Origins of gas in coal

• Coal seam gas usually the result of degradation of coal

• Two main routes• Thermogenic – produced

during coalification due to heat and pressure over time

• Biogenic – derived through microbial processes

• Biogenic • Primary – at an early stage

of coalification

• Secondary – after coalification with the uplift of coal

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From Faiz et al., 2012

Co

alification

Greater d

epth

Primary biogenic gas

Coal rank for Australian basins

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Increasing thermogenicmethane Faiz et al. 2012

(hydrolysis & liquefaction)

• Anaerobic degradation of the coal to methane occurs through a microbial consortia following a chain of inter-mediate organic compounds and microbes

• Similar process to bio-degradation of other organic materials

• The last step is performed by the archaea

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Biogenic methanogenesis

From Moore, 2012

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Origins of coal seam methane: US data

From Strąpoć et al, 2011

Isotope ratio

Deuterium-hydrogen and carbon 13 isotope ratios

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Origins of coal seam methane: Australian data

Faiz et al. 2012

• Not all of the coal is bio-available

• A proportion of the volatile fraction may be degraded

• But this can represent a significant fraction of the coal depending on rank • Access of microbes to the coal micro-porosity will be

an important factor as well

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Biogenic methanogenesis from coal

From Mesle et al, 2013

These compounds will make up the volatile fraction of coal

• Limited by temperature –meso to thermo-philic range is 20 -70C with microbial activity decreasing above this – upper limit 110C

• Cover the depths of interest for coal seam gas production

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Biogenic methanogenesisand temperature

From Mesle et al, 2013

• Coal seams contain the organic matter to sustain microbial communities • Nutrients are also required (nitrogen, phosphorus and potassium)• Nutrients from surface in groundwater recharge are depleted with flow in the

sub-surface

• Shallow coal seams • may receive sufficient nutrients via groundwater flow

• For deeper coal seams • groundwater will be very low in nutrients • Under insitu conditions the nutrients required for microbial growth derived from the coal

during degradation• Natural rates of biogenic methanogenesis within deeper coals very low – nutrient limited?

• Adding nutrients to coal seam reservoir formation waters could stimulate in-situ methanogenesis - biostimulation

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Nutrients and Biogenic methane

Coal physical structure• Fractured rock with dual porosity structure

• Cleats - the macro-porosity and coal matrix - the micro-porosity

• Bulk flow occurs in fracture system

• Dissolved nutrients could diffuse into micro-porosity but size of bacteria could restrict them to cleat surfaces

matrixFrom Moore, 2012

Plan view

Laubach et al 1998

Cross – section

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• A number of studies have demonstrated stimulation of biogenic methanogenesis from coal through nutrient amendment of formation waters

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Biostimulation of coal methanogenesis

Anaerobic bioreactor @ atmospheric pressure

Crushed coal

Nutrient augmented formation water

Helium headspace

Headspace samples to monitor gas generation

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Previous studies: Example resultsPapendick et al. 2011

Green et al. 2008

• Gas generation varied significantly; a function of• coal, the endemic microbial community and various experimental conditions including particle size, pH, nutrient concentrations, temperature etc

• Plateau in gas generation commonly observed• could be due to depletion of readily degradable coal, accumulation of toxic organics, depletion of nutrients

Laboratory studies under reservoir conditions

• Previous work has used crushed coal at atmospheric pressure and reservoir temperature

• Good gas generation rates observed

• How does this translate to reservoir pressure and intact coal?

• Core flooding experiments using intact coal replicate many of the key reservoir conditions

• This study conducted core flooding experiments • under anaerobic conditions

• using nutrient amended formation waters

• with coal core

• at reservoir pressure and temperature

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Core flooding rig

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Confining pressure control pump

Pressure vessel

Core sample with membrane

Water pump

Confining fluid

Gas pumpHelium pump

GC/MSGas analysis

SpectrophotometerNutrient analysis

2-Phase separator

Gas/water sample port

Inflow arrangement

Outflow

Inflow nutrient mixture vessel

• High pressure syringe pumps provide precise pressure and volume control and measurement

• Two phase separator on outflow to monitor gas or water flow

Methodology

1. Degassing of coal core before flood & determination of any residual gas pressure

2. Core flood with nutrient augmented formation water• Periodic water sampling and analysis of

– Nutrient concentration inflow and outflow

– Dissolved gas partial pressure

• Pore pressure - 5 MPa

• Generated gas is adsorbed no gas outflow during experiment

3. Degassing of core sample• Decrease pore pressure

• Helium flood - composition analysed

• Vacuuming stage for <1 atm pressures

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Example experimental observations: core flood#1

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0

1

2

3

4

5

6

7

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0

Wat

er fl

ow

rat

e (m

l/d

ay)

Time (days)

0

2

4

6

8

10

12

14

16

18

Par

tial

Pre

ssu

re (a

tm)

Time (days)

Methane

Carbon dioxide

Water flow rate Gas partial pressure in outflow water

0

0.002

0.004

0.006

0.008

0.01

0.012

0 20 40 60 80

Cu

mu

lati

ve u

pta

ke, m

g/g

coal

Time, days

Cumulative Uptake

N

P

0

0.00005

0.0001

0.00015

0.0002

0.00025

0.0003

0 20 40 60 80

Up

take

rate

, mg/

g co

al

Time, days

Uptake Rate

N

P

Nutrient balance

Nutirent1

Nutirent2

Nutirent1

Nutirent2

Gas generation: core flood #1

• Gas recovered from core at end of core flood

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0

0.2

0.4

0.6

0.8

1

1.2

-1

0

1

2

3

4

5

6

CH4

gas

cont

ent

(m3 /t

onne

)

Pres

sure

(MPa

)

Pressure

Gas Content

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0 10 20 30 40 50 60 70

Cu

mu

lati

ve

up

tak

e (

mg

/g c

oa

l)

Time (days)

Cumulative Nutrient Uptake

Nutrient 1

Nutrient 2

0.0000

0.0001

0.0001

0.0002

0.0002

0.0003

0 10 20 30 40 50 60

Up

take

rat

e (m

g/g

/day

)

Time (days)

Nutrient Uptake Rate

Nutrient 1

Nutrient 2

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

Gas

Par

tial

Pre

ssu

re (

atm

)

Time (days)

Methane

Carbon dioxide

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

Flo

wra

te (m

l/m

in)

Outflow (ml/min)

Example core flood#2

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Water flow rate Gas partial pressure in outflow water

Nutrient balance

Time (days)

Sampling

Gas generation: core flood #2

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0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Gas

Co

nte

nt

(m3 /

ton

ne

)

Time (days)

Carbon dioxide

Methane

Sample vacuuming

Conclusions

• Enhancement of biogenic methanogenesis successfully demonstrated at reservoir pressure and temperature on intact coal core

• Up to 1 m3/tonne generated over ten week period

• Further work being conducted to refine nutrient management and optimise gas generation

Luke Connell