A dynamic theory of hydrocarbon migration

Abstract

This paper presents a new analysis of secondary migration of hydrocarbon that does not require capillary forces for trapping, but instead uses the method of characteristics and wave theory. The waves change speed and either reflect or refract (or partially reflect and partially refract) as they contact with layers of different flow capacities. Reflection of a certain wave from a boundary starts hydrocarbon accumulation below that boundary. The method is easy to use and conforms readily to graphical solution. For the sake of simplicity there is only two-phase flow. The application of this method gives new insights into the physics of migration and entrapment of oil. The method gives realistic times for oil accumulation and points to oil generation rate as the most sensitive variable. Oil and water densities, viscosities, and permeability are also important. We find that at the very small generation rates usually assumed the time required to develop a given column thickness is insensitive to the distance from the source rock. In general, the method also predicts a non-uniform saturation in the oil column caused by an interaction between buoyancy and viscous forces. Being based on the dynamic interactions of viscous and buoyancy forces, our theory is considerably at odds with hydrostatic approaches. We assume no capillary pressure, one-dimensional flow, and no regional groundwater flow, conditions which are not realized in actual migration. The theory should be viewed therefore as an end member of a more general theory; nevertheless, the largely graphical solutions give fundamental insights that are difficult to obtain by other techniques.