Fluids (e.g., oil, water, and gas) exist in a variety of materials, including geological formations. These fluids are often recovered using a well, or a borehole cut into a formation. During exploration and recovery operations, it is sometimes useful to determine the characteristics of formation fluid chemistry in real time, such as the gas-to-oil ratio (GOR).
Compositional analysis of fluids down hole can be performed using optical spectroscopy. Although such methods are explicate for some components such as methane, the results are only approximate for light end fractions, and interpretative for contamination, all such results are highly matrix dependent. That is, pressure-volume-temperature (PVT) derived properties such as the GOR are correlated, and not directly measured. A molecular weight distribution of a sample is one compositional determination that may be performed.
Other available methods to determine molecular weight include osmosis, freezing point depression, and mass spectrometry. Of these methods, only mass spectrometry, which involves delicate and expensive instrumentation, yields a molecular weight distribution without prior separation.