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Fluid sampling safety hazards
No discussion of fluid sampling would be complete without reference to the numerous hazards that must be considered when establishing safe working practices and sampling programs. Like many areas of the petroleum industry, if not managed properly, hazards can lead to equipment damage or loss, personal injury, and even death.
Hydrogen sulfide (H2S)
This poisonous chemical is present in numerous hydrocarbon reservoirs and can be present both in gas streams and dissolved in hydrocarbon liquids. Although H2S is recognizable by its smell at the low parts per million (ppm) level, above approximately 100 ppm the human nose becomes insensitive to the gas, and personnel could easily be exposed to lethal levels of H2S (700 ppm can lead to instant death) if proper safety equipment is not in use. Safety measures should range from automatic alarm systems, personal monitors, and evacuation equipment to positive-pressure breathing systems, depending on the exact nature of the risk.
Fluid sampling frequently involves pressures up to 10,000 psi (700 bar), and even higher pressures are becoming increasingly common. Basic precautions should involve careful checking that equipment has a working pressure rating compatible with the maximum pressure that can be encountered at a sampling point (beware that flowing streams can produce a "hammer" effect when valves are closed suddenly), routine wearing of eye protection, and releasing of pressure before tightening leaking connections and attaching the ends of lines used to vent pressure.
Reservoir-fluid samples contain combustible hydrocarbons, so care must be taken to eliminate all sources of ignition from areas in which samples are collected or stored, especially where hydrocarbons are released during the purging of lines. Equipment must never be pressurized with oxygen or air (e.g., to clear blockages), as this can result in autoignition of heavy hydrocarbons (the "diesel" effect).
Cleaning agents may contain dangerous compounds such as chlorinated solvents, and indeed, produced fluids may contain benzene. Breathing of vapors and skin contact with solvents should be avoided as much as possible. Solvents should be used as efficiently as possible, and all waste materials should be stored in closed containers before proper disposal.
Transport and storage
Physical shocks are common during transport, so sample containers should be shipped with connecting ports plugged and exposed valves protected by endcaps. Liquid-filled containers are at risk of developing high pressures when heated; the best protection is to collect samples so that the liquid is in two-phase condition, with a gas cap representing approximately 10% of the capacity, or to use sample containers with a special separate gas cap. Rupture disks can be used to provide similar protection, but there is an increased risk of sample loss and venting of hazardous material.
Other safety concerns
Examples of other dangers that sampling personnel must be aware of include offshore operations (special survival training is available), lack of oxygen in enclosed areas where large volumes of gases can be vented (notably nitrogen, but other gases such as hydrocarbons are an equal danger), and the toxicity of mercury, still used in some sampling operations.
Personnel who are not trained to work safely in the presence of these or other hazards must not undertake fluid-sampling activities. Assistance in properly managing all hazards should be obtained from qualified safety specialists.
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