FLUID TOPOLOGY FOR INVASION PERCOLATION IN 3-D LATTICES

A computer algorithm for the displacement of one fluid by another in three-dimensional pore-throat network models of porous media allows the determination of fluid characteristics and distributions at any point in the displacement process. The flowing fluids are found to form two closely intertwined networks with very few regions of space containing only one fluid. Further, the fraction of dead-end invader, i.e. the ratio of the fraction of nonflowing to flowing pores is essentially constant throughout a process. The dendritic character of trapped, i.e. disconnected fluid is dependent on the degree of pore-throat correlation in the network. As a result, a given pore filled with one of the fluids is likely to have at least one neighbor filled with another fluid. Our observations imply that (1) fillable pores are very likely to be filled, and (2) clusters are not compact. The latter provides a ready explanation for the ease with which so-called oil ganglia are broken up rather than moved.