Gases in Reservoirs: A Balance between Generation and Migration, Part II: Application to GOR Predictions in the North Sea

Johannes Wendebourg and Stephan Duppenbecker

In the North Sea hydrocarbon fluids with widely varying GOR are generated by two different source rocks: one from a Type II kerogen and one from a Type III kerogen. On one hand, the past thermal regime controls the timing of generation and the GOR of the fluids. On the other hand pressure regime controls how the fluids are transported and accumulated into reservoirs. The interaction between pressure and temperature controls finally the GOR in the reservoir.

An improved version of IFP's 2-D basin model has been applied on a North Sea cross section and demonstrates how the balance between generation and migration works. A deep hot overpressured zone generates fluids with high GOR and lower densities and viscosities, while a higher moderately-pressured zone exhibits only low GOR oils. The accuracy of GOR predictions depends how the hydrocarbons composition and phase split are described. A fully compositional description and a lumped description with gas and oil as two components will be compared.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California