Suction Flow Control
As discussed above, overpumping and excessive entrance velocities are the cause of many well problems, including sand pumping. For the flow of particulate matter to occur in a well, flow must be in the turbulent state. If flow were in the laminar state, there would be insufficient energy to move sand particles. When a pump suction is set above the top of a well screen, it is believed that the velocity distribution through the height of the screen is often highly variable, with the highest velocities occurring near the top of the screen. Aquastream™ is a patented suction flow control device which has been designed to more uniformly distribute flow into a well throughout the vertical well screen. The Aquastream unit is constructed of slotted PVC pipe coated with a reinforced silica sand pack, and treated with an epoxy compound. The device can act as a gravel filter pack as well as redistributing energy in the screen.
Installation of Aquastream units has proven effective in controlling sand pumping in many wells.
DEVELOPING A REHABILITATION PROGRAM
Well owners should evaluate well and pump performance on an on-going basis. Data to be collected should include static water level, pumping water level, flow rate, discharge pressure, sand production, and energy consumption. Data should be collected in a consistent manner at specified periods of time (usually monthly or quarterly). A significant change in operating conditions indicates that a problem may exist.
Once a problem has been identified, the potential sources of the problem should be evaluated. The operation history of the well should be reviewed along with the results of any previous treatment efforts. The existing data may need to be supplemented by conducting performance tests to determine the current condition of the well and pump. If it is necessary to remove the well pump, a down hole video survey should also be performed. A proper treatment procedure should then be developed to address the specific well problems.
Implementation of rehabilitation procedures for an individual well should generally include some or all of the following steps:
- Pull and inspect the pump
- Perform a video survey,
- Perform mechanical cleaning of the well screen,
- Apply the proper quantity and type of chemical treatments,
- Allow sufficient chemical reaction time,
- Remove spent chemicals from the well,
- Reinstall the well pump, and
- Conduct a performance pumping test.
CASE HISTORIES
Many wells in Colorado experience decreased yield and/or sand pumping, and can be improved by rehabilitation. The following case histories present three instances where rehabilitation has been successful.
Physical and Chemical Treatment to Restore Well Yield
A Denver Basin well for a water district in the Monument area was drilled in 1970. It was drilled to a depth of 1,765 feet, with 250 feet of Johnson well screen and 225 feet of mill slotted casing placed opposite water bearing portions of the Arapahoe aquifer. The original static water level was 561 feet, and the well capacity was reported to be 156 gpm. The well was used very little in the 19 years after its construction.
During 1989, the well pump was pulled and a down hole video survey was performed. The video survey indicated that about 80 percent of the screened area was plugged. The well was then treated using a combination of physical and chemical methods, including Sonar-Jetting, introduction of chlorine and surfactant solutions, wire brushing, and surging. The deposits were then bailed out of the well, and it was observed that significant amounts of bentonite drilling mud were being removed. Apparently, the well had not been adequately developed when it was constructed nineteen years earlier. A solution of a phosphate chemical was placed in the well to break down the drilling mud present in the formation. After additional surging and bailing, a test pump was installed in the well. The well was alternately pumped and surged until the discharge was clear. A pumping test was run and the capacity of the well was determined to be 250 gpm.
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