SEALING OF BOREHOLES

The most common use of the Everting liner mechanism is to seal the borehole against vertical flow with a blank liner. (A blank liner is a flexible liner without any attachments, tubing, etc..) This is sometimes done during the drilling process to prevent vertical migration of contaminants overnight. The liner is removed the next morning for drilling to proceed. The blank liner seals and supports the borehole while the logging tools are run in the interior (Stabilization of boreholes during logging). The blank liner is often left in place to prevent vertical migration until the blank is replaced with a Water FLUTe multi level sampling system which is built to the specifications derived from the geophysics and core results.

Blank liners are installed using either air or water as the pressurizing fluid. Air driven liners are installed from a pressure canister.

The everting liner can be installed to the bottom of the hole, or installed as far as it will travel in a selected time interval (Timed blank installations). If the liner is to be soon removed, the installation to seal most of the hole conductivity may be good enough (i.e., the timed installation). It may be preferred to not push the contents of the hole into relatively tight portions of the hole. Later, the water level in the blank liner can be pumped down to near the water table in the formation while the liner is inverted from the hole.

In tight formations, all everting liners require that the water (or air) be removed to allow the liner to descend. A Pump Tube Liner technique is available to do that. The pump tube can be left in place or inverted from the hole, leaving the blank liner in place.

Liners are most easily installed in free flowing formations with water tables less than 50 ft. below the surface. In tight formations with deep water tables, the water must be pumped from the hole as the liner descends. Under Procedures, the detailed installation procedures for a wide range of conditions are discussed. Many liners have been installed in deep, low flowing holes with deep water tables.

A new procedure has been developed for Characterization of the Formation while a blank liner is descending. The technique is based upon the fact that the liner descent rate is governed by the flow into the flow paths remaining below a descending liner. As the liner covers the flow paths, the descent rate is less.

For deep water tables, we use a "bubbler"; device to monitor the water level in the liner as the liner is installed. Normal electric tag lines are impractical for monitoring water levels in liners as water is being added.

Overall, the installation of a blank liner is relatively simple and usually done by the customer with very little training. Installations have been done in 2-18" holes. Larger and smaller holes are possible. Larger holes are easier. An aid for blank liner installation in deep holes with deep water tables is called the Linear Capstan. This motor driven device allows a strong steady tension on the liner as the water flows into the hole below the liner during the liner ascent from the hole. However, many liners have been removed with an electric or hand winch and a simple spring scale to monitor the tension on the liner. Most liners are installed and removed over a wellhead roller (see, Auxiliary equipment). The auxiliary equipment is usually rented unless many liners are to be installed.

Blank liners are sold on a per ft. price (Water FLUTe prices). The blank price is the zero port column in the price sheet.

For more information on this technique, contact us at