Necessity of Dual Injection for Gelant Placement in the High Permeability Layer of a Reservoir with Crossflow

Abstract

Summary During the water-flood in a layered reservoir, the high permeability layers will be swept first, leading to a large production of water through such layers. The oil in the adjacent lower permeability layers may be left unmoved unless water shutoff treatment is administered to the thief layers. This work considers a prototype two layer reservoir with crossflow of this nature and investigates the problem of placing a gel plug in the high permeability layer in the vicinity of a producer well for water control treatment. Due to the crossflow, the gelant injected into the high permeability layer may invade the oil zone and shut-off oil production from a part of that layer as well. The depth of the unwanted vertical travel of the gelant into the oil zone is studied through simulation for a variety of reservoir and gelant parameters. The gelant invasion of the oil zone may be reduced or completely eliminated through use of the dual injection method of placement. The situations where dual injection is necessary are identified in this study. If there is a significant flow channel near the wellbore that allows crossflow between the two layers, the dual injection method is absolutely required for acceptable gelant placement. Gravel pack completed wells also present a very similar problem due to crossflow through the gravel pack. In presence of such a crossflow channel the pressures of the two fluids in dual injection have to be matched very closely to successfully place the gelant in the thief layer.