Idealized Behavior of Solvent Banks in Stratified Reservoirs

Abstract

One of the more important problems to be solved in designing a miscible flood is related to the size of the solvent bank used. Size of the bank may be critical to economic success. Too large a bank loses money; too small a bank may deteriorate and fail to maintain the miscibility needed for high recovery.An important factor in deterioration of a small bank is permeability channeling. In a highly stratified reservoir, solvent speeds ahead in the more permeable zones and mixes laterally with fluids bypassed in adjacent, low-permeability strata. Numerical solutions have been obtained .for the differential equations that describe the movement of a slug through a two-layer system in which mixing occurs both in the direction of flow and transversely. The solvent slug is assumed to have the same density and viscosity as the resident fluid and the pushing fluid. These solutions have been verified by comparing them with similar concentration profiles obtained in the laboratory in a 36-ft stratified model packed with glass beads.The theoretical study revealed that when the dominant mechanism causing a bank to fail is lateral mixing the bank size needed for a given recovery may increase with length rather than decreasing as the square root of reservoir length, as suggested by one-dimensional mixing theory. From a comprehensive examination of the variables, a generalized correlation is developed that relates strata thicknesses, bank size, fluid velocity, mixing coefficients, system length and simple solventresident fluid phase behavior to the area miscibly swept.

Alvord [3000 ft Strawn] LPG Flood Design and Performance Evaluation

“…5.6 Later, others reported that because of viscous fingering, stratification, and gravity override, larger LPG slugs were needed. [7][8][9] From the onset of this project it was felt that a successful project required a large LPG slug (about 20% HCPV). It was also recognized that a pattern flood configuration and operating procedure would have to be adopted that would prevent the mobilized oil and the displacing LPG solvent from migrating downdip into the aquifer.…”