Hydrogen sulfide (H2S) is a toxic gas and one of the most common byproducts in the production of crude oil and natural gas. In offshore operations, hydrogen sulfide can be found in drilling fluids, recovered core samples or core barrels, and on downhole equipment. In most instances, the initial sources of hydrogen sulfide are small in volume, but can easily reach dangerous quantities; hence the need to protect personnel from the dangers of sour gas.
A variety of gas detection instruments are available for the detection of hydrogen sulfide. Solid state and electrochemical sensors are two widely used types in offshore installations. These instruments provide coverage at short ranges, around 1 - 5 meters, and are capable of establishing the presence of the gas at concentrations well below the Threshold Limit Value (TLV) of the gas. Equally important, the solid state and electrochemical devices offer quick response and stability. Such combination makes them suitable for use in harsh environments.
Recently ultrasonic gas leak detectors have also been employed as a last protective layer in the detection of hydrogen sulfide. Unlike point conventional detectors, the ultrasonic gas leak monitors supervise wide areas for high pressure sources of the gas. They do so by measuring the airborne ultrasound produced by a leak above a pre-defined threshold, providing a measure of the leak rate. These non-concentration based detectors do not require transport of the gas to the sensor, and in low noise environments, are capable of detecting leaks as low as 0.01 kg/s.
This paper examines the use of various detection techniques for improving the performance of hydrogen sulfide detection systems. An example of an oil and gas development project in central Asia is shown. Such case illustrates that a combination of different sensor technologies can enhance overall plant safety; and consequently, reduce the risk associated with the extraction of hydrogen sulfide in offshore facilities.