Unraveling secondary migration effects through the regional evaluation of PVT data: a case study from Quadrant 25, NOCS

PVT data offer a unique source of information for the characterization of hydrocarbon migration from a petroleum exploration point of view. A case study is presented here in which a large fluid compositional variability encountered in the northern half of Quadrant 25, Norwegian North Sea, and especially the enigmatic occurrence of an undersaturated light oil in a shallow Jurassic reservoir in well 25/6-1, are explained using PVT data. Recognition and numerical simulation of the effects of phase separation allowed the characterization of genetic fluid relationships and regional migration trends. Sequential flash calculations indicated the most likely formation mechanism for the 25/6-1 fluid, which is by condensation out of a migrating saturated gas phase. The volumetrics involved in this process indicate that the gas phase predominated, with only 3 vol.% of the original fluid ending up as a liquid.