Abstract: Multi-Disciplinary Approach to Modeling Secondary Migration, A Central North Sea Example

William A. Symington, Jie Huang, Kenneth E. Green, Robert J. Pottorf, Lori L. Summa

Numerical simulations assist in understanding secondary migration, and can help estimate which traps in a basin may have received a hydrocarbon charge. This is illustrated by a suite of numerical models used to understand secondary migration into a recent Upper Jurassic Fulmar discovery in the Central North Sea. The models included areal calculations using Exxon's proprietary reservoir simulator, and cross-section calculations using TEMISPACK, a commercial basin modeling package.

The areal calculations provide information about migration timing and the fill history of several traps sourced from the mature Kimmeridge source rocks in the local drainage area. Several model runs were used to evaluate the sensitivity of migration timing to carrier bed permeability and capillary pressure characteristics. Calculations indicated that for reservoir quality carrier beds (permeability > = 1 md) secondary migration can be geologically instantaneous, and that even low permeability silts can serve as effective migration pathways.

A cross-sectional model was used to integrate cross-stratal and strata-parallel migration. The model included hydrocarbon expulsion from Kimmeridge source rocks into the Fulmar sandstone, lateral migration up the flank of the structure, and vertical leakage into younger sections. The calculation suggests a portion of the top seal was breached 10-20 Ma. Several observations support this result. First, a seismic chimney is interpreted above the predicted breached seal. Second, an on-structure well encountered hydrocarbon-stained rocks but no present accumulation. Third, analysis of authigenic cements, particularly the K/Ar ages of fibrous illite, suggests that hydrocarbons occupied the trap until (approx.) 10 Ma. Finally, hydrocarbons in nearby Tertiary reservoirs can be geochemically t ed to the same source rocks as the remaining Jurassic accumulation. Analysis of hydrocarbon fluid inclusions further indicates that hydrocarbons entered these Tertiary reservoirs less than (approx.) 10 Ma.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994