Fluid Evaluation of Light Oil-Gas Accumulations with Gas Logging in Bohai Oilfield

Light oil and gas are mostly accumulated in middle-deep formations in the Bohai oilfield. Owing to the low density and high gas/oil ratio of the crude oil, gas coexists with oil. Light oil usually has similar mud logging curves with gas layers. In addition to it, logging data are deficient in some of the wells because of bad borehole conditions. These lead to the difficulties in fluid identification. Therefore, research for light fluid evaluation has been taken for the commonly used gas logging system. The 3H combined model based on conventional gas components (C₁-C₅) shows certain regular pattern which is quite different from traditional 3H model. Condensate gas and light oil as well as the interface of them are effectively recognized by the combination of 3H model and star charts, which are used to identify the fluid phase. Three fluid indexes based on C₁-C₈ detected by FLAIR system can sensitively reflect the abundance of hydrocarbon. They have obvious advantages in fluid evaluation of light oil-gas reservoir in the Bohai oilfield. The research promotes the recognition of oil and gas distribution pattern and reserve confirmation of the structural belt and is valuable for further application to other light oil-gas zones.