laboratory experiments at reservoir pressure and
TRANSCRIPT
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
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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
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