The need to provide a seal in a pipe or well casing at a point remote from the surface has resulted in the design of a great number of different methods and related equipment. Most are designed to function under special conditions, including those found in deep wells where high temperatures and pressures or corrosive materials are encountered. While such sealing means are for the most part adequate for the purpose, they are too complex and expensive for applications in more moderate environments.
One area where there is a need for a simple, inexpensive remotely actuated seal is in the remediation of contaminated vadose zone soil through the operation of soil venting wells. Soil venting is an in-situ method of extracting vapor from volatile and semivolatile petroleum hydrocarbons and removing adsorbed liquid hydrocarbons from the vadose zone. In this method air is drawn between soil particles to volatilize the contaminant and accelerate the evaporation rate of the adsorbed hydrocarbons, and is then vented to the surface through vent wells.
In carrying out a soil venting process a relatively shallow wellbore is drilled in the vadose zone and a casing containing openings for the passage of air is installed. Typically, the casing includes a screened section for this purpose which extends for a substantial distance along the length of the casing. When suction is drawn on the vent well to draw air from the surface down through the soil, the air tends to follow the shortest flow path from the area immediately surrounding the wellbore to the upper portion of the screened section. To change the flow path in order to treat soil outside of this area it has been suggested to seal off the portion of the casing screen through which air has been flowing to force the air to flow through a lower section of the screen. To accomplish this, however, an economical, efficient sealing mechanism is required. Although existing packers could be modified to allow them to seal a longer length of a casing screen, the complexity and expense of the modified packers would be out of proportion to the relatively inexpensive venting operation.
There is thus a need for an efficient means of simple design for sealing a long section of screened casing in a vent well, and it is an object of the invention to provide a method and apparatus for that purpose.