The following are the major non-hydrogen components of natural gas and crude oil production.
- sulphur compounds
- carbon dioxide
p.s. the list is not all inclusive but rather the most common ones.
1. Sulphur compounds
- generally present in reservoirs and are contaminants
- main compounds are
- H2S : Hydrogen Sulphide – highly toxic and corrosive gas
- COS: Carbonyl Sulphide
- RSH: Mercaptan; R – represents an alkyl group CH3
- must be removed from from petroleum products
- in general, contract requirements for the purchase of LNG normally state that the final product should contain less than 0.003% – 0.005% hydrogen sulphide.
- some of the method to eliminated hydrogen sulphide from products are Amine Regeneration, Caustic Washing, Molecular Sieving, Merox Treating and Iron Sponge.
- universal contaminate in reservoir
- free water is removed from oil and gas streams by means of seperator.
- one of the biggest problem due to water is the formation of hydrates
- hydrates: crystalline solid structure formed when the gas is cooled after the reservoir or in pipelines.
- hydrates can be removed by inhibitors that lower the freezing point of water and dissolve the ice structure or by absorption techniques, which removes the water from the gas
3. Carbon Dioxide
- can exist in large concentrations in a well stream
- very corrosive in the presence of water and it lowers the heating value of natural gas because of its low boiling point (-1100F at 14.7 psia)
- therefore, must be removed.
- Usually can be removed along with hydrogen sulphide in many desulphurization process with no double processing required.
- appears naturally in natural gas
- colorless, odorless, inert gas
- it simply occupies volume or space
- lower the heat value of gas
- commercially produced during the liquefaction of natural gas
- when natural gas is cooled to a liquid phase, helium remains in the vapor phase due to its low boiling point (-268.5 Deg C) which makes helium when extracted an excellent refrigerant.
- extracted helium is a valuable by-product of natural gas, but left in the gas, it lowers the heat value.
- not a natural contaminant
- appears due to leakage of air into low pressure production systems
- oxygen can be very corrosive in the presence of water vapor
- mixed with hydrocarbons could be explosive
- when equipment is shutdown for entry, the atmosphere must be tested for an adequate oxygen content, but, must be removed before re-commissioning
- metallic compounds – sodium, calcium, magnesium which are contained the brine that accompanies the well fluids. Also includes group of metals include Vanadium, Nickel, Cobalt and Iron
- solid particles – asphaltenes and resins (suspended in crude). These products contribute to emulsion stabilization in field processing if they settle out at the interfaces but they may also cause foaming.
- Wax deposit – maybe present due to the lowering of temperatures until the wax comes out of solution or as a result of flashing of the crude oil in flow equipment
- NORM – Naturally Occurring Radioactive Materials, present in reservoir rock structures and are associated with well fluid production. Radioactive scale can contaminate downhole tubing and surface production equipment, which must be identified and tested for prior to equipment entry
- Arsenic and mercury – materials are both toxic and may also cause corrosion and catalyst poisoning.
- Carbon dioxide and sulphur gases can dissolve in water to form acid.
- acids are chemically active compounds that react with the material of construction of paperwork, vessels and equipment to produce corrosion products.
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