Compound class oil fingerprinting techniques using comprehensive two-dimensional gas chromatography (GC×GC)

Determination of connectivity is of primary importance in petroleum reservoir characterization. Lack of connectivity can occur when the communication between two oil-producing zones is restricted. This subsurface condition is referred to as reservoir compartmentalization. Recognition of compartmentalization is often achieved by establishing whether two or more oils have the same molecular composition and hence are consistent with an equilibrium condition within a reservoir. Gas chromatography (GC) is one standard technique used to measure oil similarity. However, it is severely limited in the number of compounds that can be resolved in fluids as complex as oil. Comprehensive two-dimensional gas chromatography (GC×GC) greatly expands the resolution of compounds in such complex mixtures. In this study, GC×GC was used to compare the molecular compositions of two pairs of oil samples collected directly at depth within a reservoir drill hole. The first pair was sequentially sampled at the same depth and should represent the same oil. The second pair was collected from two different wells that were intersected by a permeable sedimentary horizon. The four samples were compared to each other and to a control sample using a novel comparative technique involving the separation of oil compositions into compound classes that are compared across a series of retention index ranges. These techniques were used to determine the compositional similarity of two or more oils, providing a more complete compositional comparison than possible with gas chromatography–mass spectrometry (GC–MS) and GC–flame ionization detection (GC–FID).