Hydrodynamics of Fluid Injection1
A more complete theory than has heretofore been available for the flow of slightly compressible fluids in multilayered porous systems predicts the effects of injecting into a permeable layer (aquifer) and also the consequent effects in adjacent confining beds of relatively low permeability (aquitards). Pressure buildup in a multilayered system depends on the degree of communication that develops within the system between aquifer and aquitard. This communication can be characterized in terms of dimensionless parameters β and r/B, which are functions of the permeabilities, storage coefficients, and bed thicknesses. Analytical equations for a three-layer system have been evaluated for typical values of β and r/ß, and the results have been verified by independent numerical methods.
This new theory provides a basis for understanding the hydrodynamics of fluid injection in multilayered systems. It also leads to the ratio method of determining hydraulic properties of aquitards; applications of the method to two examples of field data provide confirming data. By considering multilayered systems under quasi—steady-state conditions, a conservative method of evaluating leakage through an aquitard can be made. One can therefore determine how effectively fluids injected in any given aquifer are retained within that layer. Such knowledge is of vital importance if environmental problems resulting from an unexpected migration of toxic or otherwise undesirable fluids are to be avoided.