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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



1. FORMATION OF H2S in

RESERVOIRS



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



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



1.2. Sulfate Reduction Reaction

SO42- + 8e + 10 H+ H2S +H2O



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



SRB Activity in changing

Temperature and Pressure



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



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



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 .



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. .



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.



2.3.2 Sulfide Stress Cracking

Reaction

Fe + HFe + H22SS FeS + HFeS + H22



Schematics for Sulfide Stress

Cracking



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.



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



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



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.




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..




--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



3.2. Impacts of HH22S on HumanS on Human

HealthHealth

FlammabilityFlammability

ToxicityToxicity



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;




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.




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



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..



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¶



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



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



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



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.




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¶.




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.



4.2 Controlling Reservoir Souring

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