1. Field of the Invention
This invention concerns borehole injection procedures and apparatus, in general. More specifically, it deals with a method and apparatus for controlling the injection profile of a borehole. The apparatus may also be useful in connection with cleaning a well-bore.
2. Description of the Prior Art
In carrying out injection procedures in boreholes, e.g. in connection with secondary recovery, the injection profiles obtained in the past have often been relatively poor because of the tendency of injected fluid to flow into formations at the point or points of least resistance. Thus, in a borehole where there is a variation in the permeability of the formations down hole, the spread of injection fluid (other factors being equal) tends to be in proportion to the permeability variation over the face of the borehole being subjected to injection. Consequently, highly permeable zones are swept rapidly while low permeability zones may have very little injection fluid introduced therein.
Also, when steam injection is employed, the condensed water which tends to form adds to the difficulties. This is because water in the borehole results in additional restriction of the injected steam, so that only a limited portion of the exposed borehole face may actually have the steam injected.
Furthermore, when the base of injection tubing is located opposite an exposed borehole formation, the fluid injection tends to concentrate at that point. It may be that water above and below limits the permeability to other fluids. Consequently, after injection fluid has entered the formation it tends to be confined vertically along bedding planes so that vertical coverage along the borehole may not be increased to any appreciable extent.
Consequently, it is an object of this invention to provide a method and apparatus that will permit the control of the rate of injection of an injection fluid over an entire borehole formation that is to be subjected to injection. In this manner an injection profile may be controlled so that improved reservoir sweep may be obtained for providing better and more economic flooding operations.