Compatibility of Injection Fluids with Reservoir Components1
Deep-well disposal of wastes has proved to be feasible in certain geologic areas. The success of such an operation depends on a thorough investigation of all pertinent parameters before starting fluid injection. Possible interactions of waste fluids with reservoir fluids and rocks are among factors that should be understood.
Possible reactions between formation water and injection fluid may require that buffer solutions be used to help prevent the development of precipitates. Such precipitates can cause plugging of pore spaces to reduce rock permeability.
Some formations contain clays that may swell or migrate when contacted by foreign solutions. Subsequent bridging of the migrating clays at flow restrictions may cause severe plugging of natural flow channels and shorten the useful life of the well. Proper pH control of injected fluid can minimize clay migration. It is also desirable to maintain a constant chemical composition of the injected fluid at all times.
In some instances, injection fluid will react chemically with the reservoir rock, and such reactions could eventually result in a plugging action. The effect of precipitates on injectivity will depend on flow geometry of the reservoir, and matrix permeability will be more seriously affected than fracture permeability. Thus, an operator must be selective in the type of formation into which any waste is injected. Because there are many reservoirs with marked differences in composition and properties, and many types of wastes to dispose of, it is mandatory to investigate thoroughly each specific combination before injection is started.