Hydrodynamic Shape of Oil Stringers

Z. He, I. Lerche

A discussion is presented of the behavior of a thin oil stringer under hydrodynamic conditions in a confined aquifer. The appropriate formulae for describing the length of an oil stringer are presented, and the conditions of derivation and application of the relevant results are spelled out. A novel formula is provided to predict the maximum oil column that can be trapped by a downdip flow of water in a stratigraphic trap.

We also present a discussion of the shape of an oil stringer in terms of the stringer's width variation along the aquifer under different hydrodynamic and stratigraphic conditions. To understand the influence of various factors on the shape of the oil stringer, several synthetic cases are simulated. The variables include (1) lateral stratigraphic variation in terms of permeability changes, (2) flow rate through the aquifer, (3) interfacial tension between oil and water, (4) amount of oil in the stringer, (5) tilt angle of the aquifer, (6) densities of oil and water, and (7) viscosity of water. The shape and stability of the oil stringer can be predicted, thus providing useful constraints in hydrocarbon migration assessments.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.