The present invention provides a simple, robust, and versatile high-resolution
spectrometer that is suitable for downhole use. The present invention provides a method and apparatus incorporating a
spinning, oscillating or stepping optical
interference filter to change the angle at which light passes through the filters after passing through a sample under analysis downhole. As each filter is tilted, the color or
wavelength of light passed by the filter changes. Black plates are placed between the filters to isolate each filter's
photodiode. The
spectrometer of the present invention is suitable for use with a wire line formation tester, such as the Baker Atlas Reservation Characterization Instrument to provide supplemental analysis and monitoring of sample
clean up. The present invention is also suitable for deployment in a monitoring while drilling environment. The present invention provides a
high resolution spectometer which enables quantification of a
crude oil's percentage of aromatics, olefins, and saturates to estimate a sample's
gas oil ratio (GOR). Gases such as CO2 are also detectable. The percentage of oil-based mud filtrate
contamination in a
crude oil sample can be estimated with the present invention by using a suitable
training set and
chemometrics, a neural network, or other type of
correlation method.