• Water and steam – used extensively in processes such as system cooling, lubrication (drilling muds) and sea water for fire deluge
Water flooding and steam flooding are frequently used as advanced recovery methods to increase reservoir pressure to “push” hydrocarbons out. This usually requires the use of injection wells and is often
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used to deal with problems such as loss of reservoir pressure or high oil viscosity. This can increase the amount of oil ultimately recoverable.
A method of thermal recovery is often used in which a well is injected with steam which is then put back in production. Cyclic steam injection is used extensively in heavy-oil reservoirs, tar sands, and in some cases to improve injectivity before steam flood or in situ combustion operations. Steam is used in re-boilers onshore.
– Hazards associated with high pressure and high temperature water and steam are pressure injection of fluids into the body, as well as severe steam burns. Exposure to inhalation of high concentrations of steam can cause burning in the lungs and even asphyxiation.
– Safe handling procedures must be in place, together with the use of appropriate water and heat-proof clothing to resist steam burns. • Mercaptans – a group of sulphur-containing organic
chemical substances, with offensive odours such as rotting cabbage, which make them very noticeable in the air. They are sometimes used as an odorising agent in natural gas to make it detectable.
Gas and oil streams coming from well heads contain sour gas (the “rotten eggs” of hydrogen sulphide), and inlet oil and gas will also contain mercaptans, which are offensive in odour. Methyl and ethyl mercaptan have higher odour detectibility as they are more volatile.
Processes are in place in oil refineries and natural gas processing plants that remove hydrogen sulphide and mercaptans - known as “sweeteners”, they remove the sour, foul odours.
Leaks or discharges of mercaptans are easily detected, and lead to headaches and nausea when inhaled, accompanied by vomiting. Coughing, irritation of the lungs and inflammation of the eyes may result. Very high concentrations may lead to breathing difficulties and cyanosis (turning blue), loss of consciousness and muscle spasms. Appropriate respiratory protective equipment (RPE) should be worn where potentially harmful levels may be present.
• Drilling muds – (also known as drilling fluids), are used in drilling deep holes, as in oil and gas extraction. The mud is often an integral part of the process, serving a number of functions, but particularly as a lubricant. Drilling muds cut down the friction experienced, lower the heat and reduce the chances of friction-related complications. The mud also acts as a carrier for the materials through which drilling takes place, suspending it and carrying it up to the surface. Different muds will be used in different circumstances, based on their viscosity and density. Muds can be water (aqueous) based, non-aqueous
based, such as oil-based muds, or gaseous fluids (gas based), and may contain minerals or be totally synthetic in nature.
– Aqueous-based muds start with water (sometimes working just with water) then clays (e.g. bentonite or “gel”) and other chemicals (e.g. potassium formate) are incorporated, to create a blend resembling a dark chocolate liquid. The fluid flows freely while being pumped and when static “gels” and resists flow, until being pumped again.
– Oil-based muds often use diesel fuel as their base, which gives better lubrication than aqueous muds, cleans more easily (within the core) and has less viscosity.
– Gaseous-based muds often use compressed air alone or air/water mixtures, sometimes having polymer-type chemicals added (such as anti- foaming agents).
– Synthetic drilling-fluids are more often used offshore as they have all the properties of oil- based mud but less toxicity (e.g. than from diesel fumes).
– Hazards associated with drilling muds include contact with the additives (e.g. diesel oil and its fumes, anti-foaming agents), and the natural gases and flammable materials that can be returned to the drilling work areas, leading to a fire or explosion risk, especially around shale shaker/conveyor areas, before being returned to the mud pits.
– Suitable controls will include fire safety precautions, and appropriate PPE to prevent unnecessary skin contact with the muds. • Sludges – (drilling wastes) including low specific
activity (LSA) sludges. Depending on the nature of the base (the geological formation) being drilled for oil and gas, there may be naturally-occurring radionuclides, such as uranium and thorium, (referred to as NORM – Naturally Occurring Radioactive Materials). LSA are routinely found in both onshore and offshore activities.
They will be contained in the brine solution (formation water) that is around the pockets of oil and gas, and will be contained within the drilling content and returned to the surface. On the surface, the brine is separated from the oil and gas, which is referred to as “produced water”.
The radioactive decay products (usually radium) may dissolve in the brine, and can stay in solution or settle out to form sludges in tanks and mud pits, or form mineral scale inside pipelines and drilling components.
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Radiation levels will vary greatly depending on the geological nature of the site, but monitoring will be required in settling-out areas on the surface to ensure safety.
LSA scale in connection with oil production is mainly composed of precipitated calcium carbonate or barium sulphate (barite) which co-precipitate with naturally-occurring radium leached out of the reservoir rock. Some levels of strontium may also be involved.
The activity of LSA scale depends on how much radium is present, and the content of radium will vary with the type of rock and its content of uranium and thorium. LSA scale is not easily soluble, and its removal from production equipment requires the use of specialist dispersal chemicals or high pressure water flushing. It is important that all personnel working with LSA scale protect themselves and others from contact with radioactive materials. Extra care must be taken to avoid inhalation or ingestion of these materials as alpha radiation has a long half-life and will take a very long term to be removed from the body.
LSA sludges vary from standard sludge, through soft, easily removed scales, to very hard and tenacious scales, and the levels of radio activity will vary from just above “background” to levels requiring restricted, controlled areas and classified workers. LSA scale is classed as a radioactive substance and its handling and disposal could present occupational health and hygiene risks. Operators must develop and put in place effective procedures that recognise the hazards, protect workers from harmful exposure, minimise interference with the environment and ensure that national and international regulations are followed. In gas production areas LSA can be in the form of lead-scale. Pyrophoric iron is often found in sludges offshore and onshore and needs special control measures for its disposal because of its properties. In oil and gas production LSA scale is typically found in:
– The production well. – Safety valves. – Well heads. – Production manifolds. – Inside separators. – Water separators.
Revision Questions
7. Explain Lower and Upper Flammability Limits. 8. Explain the meaning of the classification
‘carcinogenic’.
9. What are the main dangers associated with LPG?
10. What is the purpose of anti-foaming agents? 11. What term is applied to drilling wastes
that contain naturally occurring radioactive materials (NORMs)?
(Suggested Answers are at the end of Unit IOG1.)