MIL-HDBK-1164
been added to blow the water through the screen. The water will not freeze if there are
11 pounds (5 kg) or approximately 1.5 gallons (5 L) of water in the well casing for each
pound (450 g) of dry ice added.
(2)
Provide a pressure gage on the well casing and seal the
well to prevent loss of carbon dioxide. When the gas is released, it expands and
creates a surging action that produces backpressure and backwashing of the screens.
The escape of gas through the water-bearing strata will be evident from irregular
movement of the pressure gage needle. The particular conditions involved are
different in practically all cases, and the exact procedure depends largely on the
operator's judgment.
Caution: Dry ice may cause "burns" if handled with bare hands. Use
heavy gloves or tongs. Also, since high pressure may develop during dry ice
treatment, provide for control and release of excessive pressure (150 psi or 1,030 kPa).
The gas is suffocating. Provide ample ventilation.
e)
Jet Cleaning. Horizontal jet cleaning of wells is performed from
inside the well screen. The process requires only a relatively simple jetting tool, along
with a high-pressure pump, a hose, a string of 2-inch (50-mm) pipe, and an adequate
water supply. The jetting tool itself is shown on Figure 3. It consists of an attachment
fitted with one to four horizontal nozzles (3/16-, 1/4-, or 3/8-inch [5-, 6-, 10-mm])
orifices. The bottom of the tool is closed. The upper end is threaded so that the tool
can be screwed into the lower end of the string of 2-inch (50-mm) pipe. Follow these
steps to jet clean a well screen:
(1)
Select a nozzle to match the output of the high-pressure
pump used and the well pump (Table 3).
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