The Geospect Catalytic Combustion Gas detector (ML 18IR) utilizes an infrared sensor that is tuned to the area of the infrared spectrum that is absorbed by hydrocarbons. Infrared sensors have a light source, a filter, and a sensor. The filter filters all of the light except for the infrared spectra in the hydrocarbon range. As hydrocarbon gas passes over the sensor some of the infrared light is absorbed. The sensor the detects the amount of light remaining after said absorption. The Geospect instrument then converts those differences in infrared light intensity to electrical signals, and finally to digital gas readings.
Dual Sensor Gas Analyzer
Over the years of developing mud logging gas detectors, we have discovered differences in the way that hotwire, and infrared detectors read gas. The most noticeable difference is when the hydrocarbon gas stream entering the detector contains only methane, or whether it also comprises heavier hydrocarbons like ethane, propane, butane, and pentane. The heavier gases cause both gas detectors to read higher than they would if exposed only to methane. The difference is that the hotwire detector reads only slighter higher when exposed to "heavies" whereas the infrared detector readings are much more pronounced when exposed to heavies. For example, when the IR detector is exposed to 1% by volume of propane it will read higher by a factor of three than it would if exposed to the same amount of methane. Therefore if the instrument is calibrated with 1% methane in air to read 100 units, it will read 300 units when exposed to 1% propane in air.
We at Geospect, after talking with some of our customers, have discovered that if both sensors are included in the gas detector that the differences in the sensor readings can be used to determine is heavies are in the gas stream. This determination can be made in real time and independently of the mudlogging chromatograph. In 2018, drilling rates are becoming faster and faster. It is of great benefit to oil companies to know the exact depth at which the heavies occurred. This is sometimes impossible to do with a standard mudlogging chromatograph, because of analysis time. Most dependable mudlogging chromatographs only take a one second sample every five minutes. That resolution is not good enough for today's fast drilling environment.
The dual sensor gas analyzer should be included on every mud logging job so that the depth that heavies have occurred can be determined more precisely than ever before.