--> Recent Advances in Evaluation of Secondary Migration: An Example from the Central North Sea Basin, by L. L. Summa, W. A. Symington, and R. J. Pottorf; #90986 (1994).

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Abstract: Recent Advances in Evaluation of Secondary Migration: An Example from the Central North Sea Basin

Lori L. Summa, William A. Symington, Robert J. Pottorf

Our technology for evaluating secondary migration is evolving toward a set of quantitative tools for risking whether a trap has received a specific hydrocarbon charge as a result of: (1) development of more sophisticated modeling capabilities, (2) increased use of authigenic cements and fluid inclusions to date secondary migration and post-emplacement trap leakage, and (3) improved integration of rock observations and numerical simulations. An integrated secondary migration model for a portion of the Central North Sea illustrates these predictive capabilities. In the model area, Jurassic reservoir sands are laterally isolated by silty mudstones, and overlain by Kimmeridge source rocks that are either marginally mature or immature. As a result of the discontinuous nature of the sands a d the lack of a mature local source, the existence of an effective migration conduit is a major risk. We suggest that long-distance lateral migration occurred through thin silt bridges connecting the reservoir sandstones: (1) reservoired hydrocarbons are more mature than local source rocks, suggesting that hydrocarbons were not locally derived, (2) fluid inclusion homogenization temperatures indicate that hydrocarbons entered the area prior to maturation of local source rocks, and (3) the sand/shale ratio of the silty units, calculated from neutron porosity and bulk density logs, implies that portions of these units could be effective conduits if 200-300 ft of hydrocarbon column were built up in reservoirs along the pathway. We used a reservoir simulator to establish the amount of low-pe meability silt required to move hydrocarbons from the mature source rocks into the updip reservoirs. For permeabilities >0.004 md, a continuous 20 ft thick silt was an effective conduit. We are currently constructing models with improved silt distribution, and have estimated the relative migration risk for upcoming prospects.

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