When Casing is Required

When Casing is Required

Wells constructed in very porous materials or in beach sands, where the water table is some distance below the surface, may have to be cased into the water stratum in order to complete a proper well. This is because a much larger flow of water is needed due to water loss to the area surrounding the well - the deeper the well, the greater the water loss and the greater the pressure.

The water fails to rise to the surface and loosened sands fall back on the jet, often locking it in place. Occasionally when jetting into the water stratum itself, the increased pressure, due to depth, coupled with the before mentioned losses, prevents the flow of jetting water to reach the top of the hole. When this happens, loosened sands in the pipe will settle and lock the jet pipe in the well. When this happens, block and tackle, or some other hoisting device, will be needed.

When installing this type of well, a device is needed to drive in the casing. This casing must be cut and threaded with couplings, in lengths to suit the installation's requirements. The same basic equipment for jetting is used. Drilling compounds (Kaolin, Bentonite, or other similar drilling compounds) are helpful. Even some form of drill as used in percussion-jet drilling attached to the jet pipe is sometimes desirable for the larger hole size needed or when drilling through harder sub-surfaces.

First, make a starting hole for the well. A starter casing may be used if desired. A settlement trench is needed from the well hole to a sizable work hole at least 30 inches deep for recirculating the work water. Add drilling compound to this work hole water. Put a pump strainer in the work hole about a foot below the water level but not on the bottom. Put a drill tool on the jet pipe slightly larger than the casing to be used. Attach a pressure hose to the drill pipe.

Someone has to maintain the proper water level and add drilling compound as required plus keep the strainer clean to maintain continuous water flow to the jet. This is the helper's job. The driller will be busy working the jet pipe.

The operator will raise and drop the jet pipe, repeatedly, turning it at the same time to make a round hole. The jet action of the pressure water will raise the drilled mud and sand to the surface where it will flow through the settlement trench to the work hole and recirculate to the jet unit. Continue until the desired depth is reached. It must be below the static level of the ground water.

While the jetting operation is taking place, the drilling compound will line and seal the walls of the drill hole. It is necessary to keep enough compound in the drilling water so water isn't lost when the drilling is stopped. The drill hole must be kept full of water even when the jet pipe is raised and kept full until the casing, which is prepared in advance, is installed in the drill hole and held in place until the sands close in around it.

While jetting the hole to the proper depth, the well screen and well pipe are being prepared for installation. After reaching the desired depth, the hole must be kept filled with water until the well screen and well pipe are installed. After this, the water can be turned off.

It is desirable to pour or pump some clean water down the well pipe and out through the well screen to wash out as much of the drilling mud as possible. The well should then be developed as described earlier. A well seal should be placed between the inner well pipe and the casing and any exterior annular space.