  Quantifying spontaneous, fugitive and venting related methane emissions are
often difficult and cumbersome. However, auditing the methane emissions due to
conventional and un-conventional hydrocarbon exploitation techniques are
becoming necessary. Present generation compact chemical sensors are slower,
degrade very fast, and are sensitive broad-spectrum gases. On the other hand,
optical sensors are very fast in detection of gases and more precise and can be
easily employed in various environments like boreholes and soils. In this
study, we report development of an optical sensor that is methane specific,
fast for real time applications and has tremendous application potential in the
exploration of coal bed methane and other hydrocarbon reserves with methane as
a major constituent. The detection process is based on the principle of
spectroscopic absorption of light. The detector, NiSi Schottky diode, was
fabricated and characterized exclusively for the 1.65 um, narrow bandwidth
methane absorption. The probe is of 20 cm length and comprises of a laser
source and the NiSi detector aligned optically. This probe can be employed in
boreholes, mine vents and soil layers for measuring real-time fluxes in methane
concentrations. From the laboratory based experiments it is observed that the
detection limits of the developed device is very low (3% by volume) and the
response time of detection is very rapid (about 2 seconds). Based on the
materials used, fabrication procedures adopted, sensitivity of the device and
its compactness, the developed sensor can be considered as a novel, economic
device for exploration of coal bed methane.
