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HYDROGEN SULFIDE INHYDROGEN SULFIDE IN
PETROLEUM INDUSTRYPETROLEUM INDUSTRY
Formation of hydrogen sulfide in petroleum
reservoirs
Effects of H2S in economic feasibility and
production efficiency
Impacts of H2S on human health
Methods of scavanging hydrogen sulfide
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1. FORMATION OF H2S in
RESERVOIRS
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Formation of hydrogen sulfide in reservoirsFormation of hydrogen sulfide in reservoirs(reservoir souring) occors when sulfate ions(reservoir souring) occors when sulfate ions
in water phase react with hydrocarbons inin water phase react with hydrocarbons inspecial conditions. That oxidizingspecial conditions. That oxidizing--reducingreducingreaction is expressed byreaction is expressed by bioticbiotic andand abioticabioticmechanisms.mechanisms.
�� Abiotic reaction is formed if temperature of Abiotic reaction is formed if temperature of reservoir is very high (above 100 C)reservoir is very high (above 100 C)
�� Biotic reaction forms with the existance of Biotic reaction forms with the existance of sulfatesulfate--reducing bacteria (SRB)reducing bacteria (SRB) as aas acatalyser instead of temperaturecatalyser instead of temperature
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1.1. Sulfate1.1. Sulfate--Reducing BacteriaReducing Bacteria
�� SRB is an anaerobic bacteria colonising inSRB is an anaerobic bacteria colonising in
irreducible water in pores, or at the water irreducible water in pores, or at the water
oil contact (usually near injection wells)oil contact (usually near injection wells)�� SRB activity increases with injection of SRB activity increases with injection of
oxygen scavangers (used for preventingoxygen scavangers (used for preventing
corrosion)corrosion)
�� SRB growth in reservoir is exponential, soSRB growth in reservoir is exponential, so
reservoir souring rate is also exponentialreservoir souring rate is also exponential
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1.2. Sulfate Reduction Reaction
SO42- + 8e + 10 H+ H2S +H2O
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1.3. Factors Affecting Reservoir
Souring Rate
Reservoir temperature and pressureReservoir temperature and pressure Amount of SRB in reservoir Amount of SRB in reservoir
Amount of Sulfate in water Amount of Sulfate in water
Hydrocarbon types and amount in water Hydrocarbon types and amount in water Chemicals added to injection water Chemicals added to injection water
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SRB Activity in changing
Temperature and Pressure
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2. EFFECTS OF H2S ON
PRODUCTION AND
ECONOMY
Loss of revenue exporting to refineryLoss of revenue exporting to refinery
Chemicals for decreasingChemicals for decreasing H2S concentration Plugging in water injection wells
Permeability reduction in reservoir
Shutting in wells due to high H2S concentration Hydrogen sulfide corrosion
Materials used for safety establishment
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2.1. Refinery Cost
Refineries use Caustics for eliminatingRefineries use Caustics for eliminating
Hydrogen sulfide by reHydrogen sulfide by re--oxidising sulfidesoxidising sulfides
to sulfate. Amount of caustics usedto sulfate. Amount of caustics useddepends on thedepends on the H2S concentration. Cost of Cost of
this operation is cut from the exportationthis operation is cut from the exportation
revenue of oil producer revenue of oil producer
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2.2. Plugging and Permeability
Reduction in Reservoir
The establishment of sulfide producingThe establishment of sulfide producing
biofilms results in formation damage bybiofilms results in formation damage by
producing extracelluar polysaccharidesproducing extracelluar polysaccharides
and precipitation of metal sulfides, causingand precipitation of metal sulfides, causing
plugging in water injection wells, andplugging in water injection wells, and
reducing permeabilityreducing permeability. . This fact increasesThis fact increasesthe injection pressure, thus requiring morethe injection pressure, thus requiring more
power to inject the same amount of water .power to inject the same amount of water .
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2.3. Hydrogen Sulfide Corrosion
Hydrogen sulfide as a weak acid of Hydrogen sulfide as a weak acid of
Ph = 3Ph = 3--4, causes iron and steel to come4, causes iron and steel to comeunder corrosion. This corrosion is namedunder corrosion. This corrosion is named
asas sulfide stress crackingsulfide stress cracking. .
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2.3.1 Sulfide Stress Cracking
H2S has a low solubility in water up to a
maximum of 400 ppm. 200 ppm is the minimum
observed threshold for sulfide stress cracking tooccor . Pyrite (FeS2), pyrrhotite (Fe7S8) and troilite
(FeS) are the most common by-products to
monitor hydrogen sulfide corrosion.
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2.3.2 Sulfide Stress Cracking
Reaction
Fe + HFe + H22SS FeS + HFeS + H22
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Schematics for Sulfide Stress
Cracking
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2.3.3 SSC Effects
SSC is a mechanical corrosion. SSC is a mechanical corrosion. AtomicAtomic
hydrogen diffuses into the metal.Metal hydrideshydrogen diffuses into the metal
.Metal hydridesareare precipitated when a limit is passed. Theprecipitated when a limit is passed. The
formation of hydrides will reduce theformation of hydrides will reduce the ductilityductility andand
deformabilitydeformability of the metalof the metal, with the equipment, with the equipment
losing its elasticity, metal parts start to break outlosing its elasticity, metal parts start to break outfrom the surface of contact. from the surface of contact.
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2.3.4 Factors Provoking SSC
HH22S concentrationS concentration
Water cut
PH Temperature
HH22S partial pressureS partial pressure
Tensile stresses
Material Selection
Friction factor between fluid and metal surface
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3. IMPACTS OF H3. IMPACTS OF H22S ONS ON
HUMAN HEALTHHUMAN HEALTH
Identity and physicalIdentity and physical--chemicalchemical
propertiesproperties
Threats to human lifeThreats to human life
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3.1.1. Identity and Properties
Hydrogen sulfide is alsoHydrogen sulfide is also known asknown as
hydrosulfurichydrosulfuric acid, hydrogen sulfuric acid,acid, hydrogen sulfuric acid,
sulfuretedsulfureted hydrogen, hepatic gas, stinkhydrogen, hepatic gas, stink
damp, sulfur damp, sulfur hydride,hydride, sulfuratedsulfurated hydrogen,hydrogen,
dihydrogendihydrogen monosulfidemonosulfide,, dihydrogendihydrogen
sulfide, and sewer gas (HSDB, 1998). Itssulfide, and sewer gas (HSDB, 1998). Its
structural formula is illustrated as Hstructural formula is illustrated as H--SS--H.H.
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3.1.2. Identity and Properties
Hydrogen sulfide is a colourless, flammable gas with
a characteristic odour of rotten eggs. Hydrogen
Sulfide¶s relative molecular mass is 34.08. Its
vapour pressure at 21.9 °C is 1929 Pa. It is solublein water; the water solubility at 20 °C is 1 g in 242
ml. The taste threshold for hydrogen sulfide in water
is between 0.05 and 0.1 mg/liter . Hydrogen sulfide is
also soluble in alcohol, ether, glycerol, gasoline,kerosene, crude oil, and carbon disulfide..
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3.1.3. Identity and Properties
--Boiling point:Boiling point: --6060°°CC
--Melting point:Melting point: --85
85
°°CC--Solubility in water, g/100 ml at 20Solubility in water, g/100 ml at 20°°C: 0.5C: 0.5
--RelativeRelative vapour vapour density (air = 1): 1.19density (air = 1): 1.19
--AutoAuto--ignition temperature: 260ignition temperature: 260°°CC
--Explosive limits,Explosive limits, volvol% in air: 4.3% in air: 4.3--4646
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3.2. Impacts of HH22S on HumanS on Human
HealthHealth
FlammabilityFlammability
ToxicityToxicity
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3.2.1.1 Flammability of HH22SS
Explosive limits,Explosive limits, volvol% in air: 4.3% in air: 4.3--4646
AutoAuto--ignition temperature: 260ignition temperature: 260°°CC
Heavier than air and can stay up to 42Heavier than air and can stay up to 42days at ground leveldays at ground level
Loses its concentration in air withLoses its concentration in air with
expansion in environmentexpansion in environment
IMPLIES;IMPLIES;
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3.2.1.2 Flammability of HH22SS
A HA H22S source (tanks, wells, flare, mud pit)S source (tanks, wells, flare, mud pit)
near near to an open flame has a great risk for to an open flame has a great risk for
combustion. combustion.
The word near depends on ambientThe word near depends on ambient
temperature, Htemperature, H22S emission temperature, theS emission temperature, the
flame source, and emission concentration of flame source, and emission concentration of
HH22S.S.
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3.2.1.3 Flammability of HH22SS
AA HH22S source (tanks, wells, flare, mud pit) near S source (tanks, wells, flare, mud pit) near
to ato a high temperature (260+high temperature (260+°°CC)) pointpoint is also ais also a
danger for combustion. danger for combustion.
Ex:Ex: Cylinders of generators in Kastel BS over 400Cylinders of generators in Kastel BS over 400 °°CC
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3.2.1.4. Flammability of HH22SS
HH22S isS is ddangerouslyangerously reactive when mixedreactive when mixed
with concentrated nitric acid or other with concentrated nitric acid or other strong oxidizing agents. Vapors willstrong oxidizing agents. Vapors will igniteignite
spontaneously when mixed with vapors of spontaneously when mixed with vapors of
chlorine, oxygenchlorine, oxygen difluoridedifluoride or nitrogenor nitrogen
trifluoridetrifluoride..
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3.2.1.5 Combustion by-products of
HH22SS
Sulfur dioxide, sulfur trioxide, carbonSulfur dioxide, sulfur trioxide, carbon
monoxide, carbon dioxide, water,monoxide, carbon dioxide, water,elemental sulfur, elemental hydrogen,elemental sulfur, elemental hydrogen,
carbonyl sulfide, carbon sulfide are thecarbonyl sulfide, carbon sulfide are the
most possible bymost possible by--products, some of whichproducts, some of which
are also toxic.are also toxic.
Note: Thanks to Head of Engineering Department for directing meNote: Thanks to Head of Engineering Department for directing me
towards µburning bytowards µburning by--products¶products¶
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3.2.2. Toxicity of HH22SS at Different
Concentrations and Time of Exposure 0.0010.001--0.13 0.13 ppmppm -- odour odour thresholdthreshold
11--5 5 ppmppm -- moderately offensivemoderately offensive odour odour and headache after 30 minand headache after 30 min
exposureexposure
2020--50 50 ppmppm -- nose, throat and lung irritation, digestive upset and lossnose, throat and lung irritation, digestive upset and loss
of appetite, sense of smell starts to become "fatigued",of appetite, sense of smell starts to become "fatigued", odour odour cannotcannotbe relied upon as a warning of exposurebe relied upon as a warning of exposure
100 100 --200 200 ppmppm -- severe nose, throat and lung irritation, ability tosevere nose, throat and lung irritation, ability to
smellsmell odour odour completely disappearscompletely disappears
250250--500 500 ppmppm -- potentially fatal buildpotentially fatal build--up of fluid in the lungsup of fluid in the lungs
(pulmonary edema) in the absence of central nervous system effects(pulmonary edema) in the absence of central nervous system effects(headache, nausea, dizziness), especially if exposure is prolonged(headache, nausea, dizziness), especially if exposure is prolonged
500500--1000 1000 ppmppm -- respiratory paralysis, irregular heart beat, collapse,respiratory paralysis, irregular heart beat, collapse,
and deathand death
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3.2.2. Toxicity of HH22SS at Different
Concentrations and Time of Exposure Prolonged exposure (for several hours or days) to concentrations asProlonged exposure (for several hours or days) to concentrations as
low as 50low as 50--100 100 ppmppm can cause a runny nose, cough, hoarseness,can cause a runny nose, cough, hoarseness,
and shortness of breath. Prolonged exposure to higher and shortness of breath. Prolonged exposure to higher
concentrations can produce bronchitis, pneumonia and a potentiallyconcentrations can produce bronchitis, pneumonia and a potentially
fatal buildfatal build--up of fluid in the lungs (pulmonary edema)up of fluid in the lungs (pulmonary edema) Direct contact with liquefied H2S escaping from a cylinder canDirect contact with liquefied H2S escaping from a cylinder can
cause frostbite (freezing of the tissue). Symptoms of frostbite includecause frostbite (freezing of the tissue). Symptoms of frostbite include
numbness, prickling and itching of the affected area. The skin maynumbness, prickling and itching of the affected area. The skin may
become white or yellow. In severe cases there may be blistering andbecome white or yellow. In severe cases there may be blistering and
tissue death (necrosis)tissue death (necrosis)
Male volunteers exposed to 100Male volunteers exposed to 100--150 150 ppmppm for as little as 2for as little as 2--15 15
minutes experienced eye irritationminutes experienced eye irritation
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4. METHODS OF SCAVANGING
HH22S AND PRECAUTIONSS AND PRECAUTIONS
Preventing reservoir souringPreventing reservoir souring
Controlling reservoir souring rateControlling reservoir souring rate
Controlling producedControlling produced HH22S and material selectionS and material selection
Safety precautionsSafety precautions
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4.1.1 Prevention of Reservoir
Souring Filtrating sulfate in injection water:Filtrating sulfate in injection water:
Sulfur is needed chemically for Sulfur is needed chemically for HH22S to form, soS to form, sofiltrating sulfur compounds basicly prevents Hfiltrating sulfur compounds basicly prevents H22SS
formation. formation. TheThe sulsulf fate reduction can beate reduction can be
achieved by usingachieved by using nanonano--filtration technologyfiltration technology. .
This technology needs a high investment, soThis technology needs a high investment, soeconomic feasibility work should be done beforeeconomic feasibility work should be done before
mantling. mantling.
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4.1.2 Prevention of Reservoir
Souring Injecting high doses of biocide beforeInjecting high doses of biocide before
souring starts:souring starts:
SRB growth is measured to be exponential up toSRB growth is measured to be exponential up to
nutrient limit is reached, so starting biocidenutrient limit is reached, so starting biocide
injection before souring, theoretically preventsinjection before souring, theoretically prevents
HH22S formation ; based on the assumption of S formation ; based on the assumption of µbiocide can reach all the reservoir¶. µbiocide can reach all the reservoir¶.
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4.1.3 Prevention of Reservoir
Souring Increasing injection water temperature:Increasing injection water temperature:
SRB activity is limited by temperatures betweenSRB activity is limited by temperatures between5050°°CC -- 70 70 °°CC, so heating the water over that, so heating the water over that
limits basicly kills the bacteria. Deciding over anlimits basicly kills the bacteria. Deciding over an
injection temperature, the cooling until it reachesinjection temperature, the cooling until it reaches
target should be taken into consideration. target should be taken into consideration.
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4.2 Controlling Reservoir Souring
Rate