Patent ID: 8445841

Claim:
Mid-infrared (MIR) spectrometer apparatus for determining the concentration of hydrocarbon components in aqueous colloidal suspensions of drilling mud being returned to the surface within an oil well borehole as drilling progresses, said apparatus comprising: a light source operable for emitting MIR light rays at an output port; a first detecting waveguide having a light ray receiving end receptive of said MIR light rays from said light source, an opposing light ray emitting end, and a top face positioned for exposure to and wetting by returning drilling mud; at least a first reference waveguide having a light ray receiving end receptive of said MIR light rays from said light source, an opposing light ray emitting end, and a top face positioned for exposure to and wetting by drilling mud being pumped to a drill bit; said first detecting waveguide being operable for responding to the MIR light ray(s) from said MIR light source by generating an evanescent wave proximate its top face, said evanescent wave reacting with molecules of interest in said returning drilling mud, thereby producing a modulated MIR light ray(s) at its light ray emitting end; said first reference waveguide being operable for responding to the MIR ray(s) from said MIR light source by generating an evanescent wave reacting with molecules of said drilling mud being pumped to said drill bit, thereby producing a modulated MIR light ray at its light ray emitting end; a MIR light ray detector including: first converter means responsive to modulated MIR light rays from said first detecting waveguide, for converting the same into a first electrical signal; second converter means responsive to modulated MIR light rays from said first reference waveguide, for converting the same into a second electrical signal; and means for subtracting said second electrical signal from said first electrical signal, for producing an output signal free of common mode signals and/or noise therebetween; and processor means receptive of said common mode free output signal from said MIR hg ray detector, for processing the same to extract spectra signals therefrom for identifying the concentration of related hydrocarbon components in said returning drilling mud.