Methods and apparatus for downhole fluids analysis

The present invention relates to the field of downhole fluid analysis applicable to formation evaluation and testing in the exploration and development of hydrocarbon-producing wells such as oil or gas wells. In particular, the invention provides methods and apparatus suitable for performing downhole analysis on fluids produced in such wells using optical techniques. A method of determining GOR comprising subjecting a fluid to spectroscopic analysis at a first wavelength sensitive to gas and a second wavelength sensitive to oil, determining a response matrix for the contribution of gas at the first and second wavelengths and the contribution of oil at the first and second wavelengths, determining a signal response vector and the two wavelengths, calculating a mass fraction vector from the response matrix and the signal response vector and using the mass fraction vector to determine GOR.