the technical challenges and origins of hydrogen … 2014 mike cooper 1st subsurface oilfield...
TRANSCRIPT
Devex 2014
Mike Cooper
1st Subsurface Oilfield Management Limited
The technical challenges and origins of hydrogen sulphide (H2S)
in the oilfields of the Moray Firth Basin in the UK North Sea.
Hydrogen Sulphide
Hydrogen Sulfide
Rotten Eggs
Dirty Den Nasty Nick Cooked Rotten Eggs
Mercaptans
Methanethiol, Ethanethiol, Propanethiol, Butanethiol,
Pentanethiol
Hydrogen sulfide, smelling of rotten eggs
Ammonium sulphide, rotten eggs
Carboxylic acids
Propionic acid, sweat
Butyric acid, rancid dairy
Valeric acid
Caproic acid, smelling of cheese
Aldehydes & Amines
Ethylamine, fishy smell
Putrescine & Cadaverine, rotten meat
Indole
Skatole, smelling of faeces
Stink Bombs
Lower Explosive Limit 4%
Upper Explosive Limit 46%(+) Explosive
Comparable in toxicity to hydrogen cyanide
100 ppm “Immediately Dangerous To Life” H2S kills
15 ppm Short-term exposure limit
Olofactory receptors in nose paralysed at ~ 100ppm
Olofactory fatigue at very low concentrations Can’t smell it
Refractive index very close to air Can’t see it
H2S +H2O – Hydrosulphuric acid (>10ppm) Irritates eyes
Health & Safety Challenges
Recognition threshold of human smell, the concentration at which
50% of humans can detect the characteristic odour of hydrogen
sulphide.
Borderline concentration for eye irritation.
Leads to eye damage.
Olfactory nerve is paralyzed after a few inhalations, and the sense of
smell disappears, often together with awareness of danger.
Pulmonary edema with the possibility of death.
Lethal concentration for 50% of population for 5 minutes exposure.
Strong stimulation of the central nervous system and rapid breathing,
leading to loss of breathing.
Immediate collapse with loss of breathing, even after a single breath.
HSE Guidelines for H2S
0.0047
800
150-250
320-530
50-100
530-1000
>1000
10-20
PPM
Heavier than air- usually falls to low-lying, poorly ventilated areas
When mixed with lighter-than-air gasses, or at high temperature it can rise.
Auto ignition temperature 232oC, (Lit cigarette – 700oC)
H2S burns with a blue flame, producing SO2 (itself poisonous) and water.
Corrosive to metals, forming metal sulphides - characteristically dark brown or black (look
out for blackened tubulars)
Engineering Challenges
Variation in measurements – sampling errors
Reservoir Concentration
0
Adsorption and reaction with sample
chamber material shows dramatic reduction
in H2S concentration over days
Days
H2S
Concentr
ation
6
After Elshahawi & Hashem, 2005
H2S concentrations vary throughout the Process
Produced
Water / Water
Injection
16 ppmw
Inlet
6,500 ppmv
equivalent
Flare
15 ppmv Gas Lift
15 ppmv
Fuel Gas
15 ppmv
Post Amine Plant
and before
Incineration
42,600 ppmv
Amine Sweetening
5,500 ppmv
Crude Oil
Cargo
5 ppmw
Study Area – Quads 14 & 15
H2S Occurrences in Study Area
40%
92%
16%
4%
4%
0.65%
1.6%
Sour Fields v Souring Oilfields
• H2S is a common feature of mature waterfloods
• The souring phenomenon is defined as the increasing mass of H2S
per unit mass of total produced fluids.
• “Sour” typically above 3ppm. (50% of people can detect 0.0047ppm
H2S.
• AWB’s – Found above 80oC. Barotolerant to at least 9500 psi.
Formation Temperature
80oC
45oC
Sulphate-rich cold injected seawater
warms through the zone where
thermophilic AWB’s are stable
After HSE Oilfield Reservoir Souring Report 1993
Distance from Wellbore
Tem
pera
ture
H2S & CO2 content varies within an accumulation……..
6,500ppm
H2S 35%wt
CO2
Not only H2S – but also CO2
Two families not obvious
on a linear scale
H2S Origins
‘Volcanic’ OAE’s SRB “Black Sea” model 87% anoxic
Black smoker (minor) & redox
Source rock
AWB “Anoxic Wee Beasties” Sulphate-reducing bacteria
Minerals
Mantle/volcanic source??
Major crustal feature at
Top Zechstein
No major H2S or CO2
concentrations in local area
No Inert Gases (N2, Ar, He, Ne, SO2 etc)
Mid-Jurassic triple junction –
this is only leg where H2S is a
major feature
Source Rock Geochemistry – Kimmeridge Clay Formation
Moderate biodegradation – influx of meteoric waters in middle
of 750ft thick shale source rock sequence
Minor biodegradation in rich source rock interval (6% TOC)
Immature rich source rock – no GC analysis of this interval (8% TOC)
LTOBM-contamination in Piper sands extract
Sulphate-rich ground water percolation may act as
Feedstock for SRB’s.
Highest H2S concentration in OMF area Gamma Ray
After Geochem Group Limited, 1991
Base Cretaceous Unconformity Structure Map
Halibut Horst
Halibut Platform
Tartan Ridge
Brochel
accumulation is very
tight suggesting local
sourcing of H2S.
Anomalous
measure?
Gamma has very
latest Jurassic
sand stringers
with low H2S &
high CO2
Late mature source
rock in Witch Ground
Graben appears to
have low H2S content
High H2S occurrences are within or
adjacent to areas of light green to
light blue on this map:-
2.4-2.9 msec TWT
Alexandria/Brule
25
5,000
40,000
4,000
1,000
6,500
16,000
1,000
2 4,000
13
15
5
80 11
6
0
0
0?
12
H2S rich gases
from the Hot
Lens sands -
Latest Jurassic
in Tartan
Perth-Dolphin-Lowlander Hub Development Area
One billion
barrels oil-in-
place
No oil
recovered to
date.
The solution is
coming….
• No definitive single source of H2S can be discriminated from available data.
• Tectonic setting within isolated extensions of the failed arm of a triple junction may account for anomalous setting.
• No evidence for mantle origin nor proximity to evaporites
• High concentrations of H2S are found in close proximity to mature source rock (i.e. short-distance migration)
• Some evidence the kerogen in immature KCF source rock has been biodegraded
• Despite being within thick shale packages
• Syn-depositional?
• Stratigraphic component to H2S distribution due to either:
• Connectivity to ?local source kitchen
• Isolated sands in late Jurassic
Conclusions
Dave Soutter
Nick Allan
Jon Ashdown
Phil Ware
John Wood
Gordon Smith
Adrian Jones
Colin Percival
Acknowledgements
