The present invention relates to compositions and methods useful in injection operations. More particularly, the present invention relates to fluids comprising water-soluble relative permeability modifiers and methods of using such fluids to divert aqueous fluids in injection operations.
Generally, in the recovery of hydrocarbons (e.g., oil) from a subterranean formation, the energy required to force the hydrocarbons into producing wells may be supplied by the natural pressure drive existing in the formation or by mechanically lifting hydrocarbons from the subterranean formation through the wells bores of producing wells to the surface. But at the end of primary recovery operations, a substantial quantity of hydrocarbons may remain in the subterranean formation. Thus, secondary recovery methods, such as injection operations, may be used. For example, in injection operations the energy for producing the remaining hydrocarbons from the subterranean formation may be supplied by the injection of fluids into the formation under pressure through one or more injection wells penetrating the formation, whereby the injection fluids drive the hydrocarbons to one or more producing wells penetrating the formation. Suitable injection fluids include, among other things, water, steam, carbon dioxide, and natural gas. The sweep efficiency of injection operations, however, may vary greatly depending on a number of factors, such as variability in the permeability of the formation. In particular, where the subterranean formation contains high permeability zones, the injection fluids may flow through the areas of least resistance, e.g., through the high permeability zones, thereby bypassing less permeable zones. While injection operations may provide the energy necessary to produce hydrocarbons from the high permeability zones, hydrocarbons contained within less permeable zones may not be driven to the one or more production wells penetrating the formation.
A variety of techniques have been attempted to improve the efficiency of injection operations. One such technique, known as “polymer flooding” comprises the addition of water-soluble polymers, such as polyacrylamide, to the injection fluid, inter alia, in order to achieve a higher viscosity injection fluid. A higher viscosity injection fluid may result in a better sweep efficiency of the injection fluid in the displacement of hydrocarbons through the formation because the viscosified injection fluid may be less likely to by-pass the hydrocarbons, leaving them behind in the formation. One drawback to this technique is that despite the increased viscosity, the polymer flood may still flow through the high permeability zones, bypassing the oil contained within less permeable zones of the formation.
Another technique to increase the efficiency of injection operations has involved the injection of a sealant, such as polymer gels, into the subterranean formation so as to plug off the high permeability zones. Thus, the flow of the injection fluids may be diverted from the high permeability zones to less permeable zones. The use of these water-blocking techniques, however, may be problematic. For example, plugging off the high permeability zones may not be suitable unless the sealant can be injected solely into the offending high permeability zones therein. Furthermore, techniques geared toward injecting sealant designed to plug off the high permeability zones are limited because they may require expensive zonal isolation. Zonal isolation also may be inaccurate, which may lead to inadvertently plugging and/or damaging additional zones other than the high permeability zone.