WELL RELINING
It is not uncommon for large-diameter water wells to suffer some damage during their
operational lifetime as a result of various down-hole procedures (e.g. redevelopment) or exposure to natural ground-water conditions. Among the more common after effects of well damage are corrosion and sanding; both conditions can seriously affect the continued use of an otherwise productive well. In some cases, depending upon the severity of the well’s condition, it may become necessary to reduce the pumping rate in order to control the problem somewhat. In the worst case, the well might have to be abandoned. However, two other options for consideration are: 1) complete relining, and 2) installing a partial liner.
Complete Relining
A relined well consists of an inner casing that extends from ground level (with an appropriate stick-up, if needed) to the bottom of the existing well casing. Generally, the outside diameter (OD) of the liner is on the order of 3 to 4 inches smaller than the inside diameter (ID) of the existing casing. Various materials such as mild steel, copper-bearing steel, high-strength low alloy steel, and stainless steel are suitable for liners, depending upon the parameters of strength and durability that are required for specific installation.
A typical complete liner includes a section of blank casing (i.e., pump chamber) that is connected to one or more sections of louvered screen or continuous wire-wrapped screen. This memorandum assumes that the well screen in the outer casing and liner are located at the bottom of the well. Often, the annular space between the liner and outer casing/screen is filled with select gravel. If a gravel pack is installed in the annular space, the apertures (i.e., slots) of the inner well screen are sized to retain 100 percent of the gravel pack material.
Installing a liner can be an effective way to deal with a structural problem in the well and might add many years to its lifetime. However, the liner can negatively impact the well’s pumping capacity because of the added well losses. Also, there is the possibility that the smaller ID of the liner might make it impossible to re-install the pump that was previously used in the well. Therefore, a new pump may be needed to meet the new physical and hydraulic conditions of the well.
Partial Liners
A partial liner is a section of casing that is secured in place within the well by various methods. Two types of commonly-used, partial liners are discussed below.
Swaged Liner
A swaged liner is a short section of casing and/or screen that essentially functions as a patch. This type of liner is installed typically with either an electric or hydraulic swage.
Electric swages are used to install corrugated steel or other thin-walled steel liners, whereas annealed steel liners are installed with a hydraulic swage. The installation procedure consists of lowering the swage and liner into position at the appropriate depth. Then, the swage is activated. It enlarges within the casing and forcibly shapes and affixes the liner to the interior of the casing. The swage is then removed from the well.
A relined well consists of an inner casing that extends from ground level (with an appropriate stick-up, if needed) to the bottom of the existing well casing. Generally, the outside diameter (OD) of the liner is on the order of 3 to 4 inches smaller than the inside diameter (ID) of the existing casing. Various materials such as mild steel, copper-bearing steel, high-strength low alloy steel, and stainless steel are suitable for liners, depending upon the parameters of strength and durability that are required for specific installation.
A typical complete liner includes a section of blank casing (i.e., pump chamber) that is connected to one or more sections of louvered screen or continuous wire-wrapped screen. This memorandum assumes that the well screen in the outer casing and liner are located at the bottom of the well. Often, the annular space between the liner and outer casing/screen is filled with select gravel. If a gravel pack is installed in the annular space, the apertures (i.e., slots) of the inner well screen are sized to retain 100 percent of the gravel pack material.
Installing a liner can be an effective way to deal with a structural problem in the well and might add many years to its lifetime. However, the liner can negatively impact the well’s pumping capacity because of the added well losses. Also, there is the possibility that the smaller ID of the liner might make it impossible to re-install the pump that was previously used in the well. Therefore, a new pump may be needed to meet the new physical and hydraulic conditions of the well.
Partial Liners
A partial liner is a section of casing that is secured in place within the well by various methods. Two types of commonly-used, partial liners are discussed below.
Swaged Liner
A swaged liner is a short section of casing and/or screen that essentially functions as a patch. This type of liner is installed typically with either an electric or hydraulic swage.
Electric swages are used to install corrugated steel or other thin-walled steel liners, whereas annealed steel liners are installed with a hydraulic swage. The installation procedure consists of lowering the swage and liner into position at the appropriate depth. Then, the swage is activated. It enlarges within the casing and forcibly shapes and affixes the liner to the interior of the casing. The swage is then removed from the well.
Drop-Off Liner
A drop-off liner typically consists of a length of either louvered or wire-wrapped screen that is installed at the bottom of the well. The liner is attached to a tool on the end of a string of drill pipe. After the liner is in place, the attachment between the liner and drill pipe is uncoupled, leaving the liner behind. The annular space between the drop-off liner and casing/screen can be filled with selected gravel. The liner installation may be completed by grouting around the top of the liner through a temporary tremie pipe