Well Development

with the waterra inertial pump

Well development is an important part of monitoring well procedures and is usually required in order to acquire a quality sample and adequately determine formation parameters such as permeability.

Fines are frequently mobile and will move from a high concentration to a low concentration. The ultimate low concentration is of course your monitoring well. Fine material will accumulate in monitors and sand packs will silt up and may require redevelopment.

Detractors from the Waterra System have frequently stated that the Inertial Pump's action on the monitoring well increases turbidity.This is true in monitoring wells that require development. In a monitor that is properly developed, the inertial pump cannot increase turbidity as the colloidal material has been removed from the well and the sand pack as per the definition of development.

suggested solution

Fortunately, the Waterra Inertial Pump has an excellent well development capacity that can be enhanced even further with the addition of the well development Surge Block Ring.

In fact, the Waterra Inertial Pump is recognized by many as one of the best development tools available today for 2 inch (5 cm) monitoring wells and certain 4 inch (10 cm) wells also. The addition of the Waterra Hydrolift II or Power Pump 2 make the system capable of developing even difficult wells of considerable depth, sometimes up to 300 feet (90 m).

The Inertial Pump produces excellent development results because of the combination of simultaneous pumping and gentle well surging. This draws fines into the well and effectively removes them. This effect is significantly enhanced with the addition of the Surge Block Ring. This plastic ring increases the outside diameter of the Standard Flow D-25 foot valve or High Flow D-32 foot valve to 1 7/8" (4.7 cm). This greatly reduces the annular gap between the valve and the well screen. With less annular gap the surging effect of the system is significantly enhanced.

The recommended solution will depend primarily on the well diameter, but depth of pumping, the amount of sediment, sediment particulate size, sediment compaction and the availability of water can all be influential factors on the equipment recommended. Some general guidelines are presented below.

two inch (5 cm) silted wells

The Standard Flow System is recommended for 2 inch (5 cm) well diameters.

In addition, numerous Waterra users have reported back on the effectiveness of also using an SBD-25 Surge Block. The Surge Block is an inexpensive doughnut shaped part that presses on top of the valve and simply increases the cross-sectional area of the valve. It creates a surging action and allows you to pump at the same time. This surging action is most effective if valve/surge block combination is located close to the water-sediment interface. The surging will "stir up" the sediment and while suspended, will be pumped up the tubing to surface. The pump needs to be lowered as the interface moves down the well.

In deeper 2 inch (5 cm) wells (greater than 130 feet (39 m)), consideration should be given to using the High Flow System.

The SBD-32 Surge Block would enhance the surging action as well.

four inch (10 cm) silted wells

The concepts as described above for two inch (5 cm) wells also apply to four inch (10 cm) wells. Four inch (10 cm) wells usually require the High Flow System. A four inch (10 cm) High Flow Surge Block is also available for the D-32 foot valve designed specifically to enhance surging in 4 inch (10 cm) wells.

Waterra also carries a four inch (10 cm) surge block for the Standard Flow System that fits onto the D-25 foot valve if the well is quite shallow (ie. less than 30 feet (9 m)).

standard flow system

The Standard Flow System usually consists of:

• a D-25 Foot valve
• a length of Standard Flow Tubing
  
• and a drive mechanism: either the manually operated Lever Pump, the electric Hydrolift-2, or the gas driven PowerPump-2

high flow system

The High Flow System usually consists of:

• a D-32 Foot valve,
  
• a length of High Flow Tubing
  
• and a drive mechanism: either the manually operated Lever Pump, the electric Hydrolift-2, or the gas driven PowerPump-2

procedure

A valve is securely threaded onto the tubing. The tubing is then inserted into the well, valve first. If a surge block is to be used it should be installed on the valve by pressing it on about halfway up the valve. The tubing is fed down to the depth of the screened interval and then cut about six feet (2 m) above the top of the well. The drive mechanism should be affixed to the well head and the tubing connected to drive mechanism at both the reciprocating arm and the fixed discharge on the drive mechanism. Pumping is initiated by turning on the drive mechanism or pumping by hand at the rate corresponding to the desired flow. The advantage of the mechanized drive systems is the fact that whilst purging, the field person is available to do other tasks.

The Inertial Pump is operated by oscillating the tubing and foot valve assembly up and down in the monitoring well. The upward stroke imparts upward momentum to the water column trapped in the tubing by the foot valve This water column continues to move upwards through the tubing because of its momentum during the pump's downward stroke and in effect draws more water into the tubing. The operation of the inertial pump causes some gentle surging and will develop most monitoring wells. It is also very effective at removing silt and clay that may have accumulated in the sump of the well.

With the addition of the surge block to the pumping system, more water is drawn into the monitoring well beneath the surge block/valve combination during the upwards stroke due to the syringe like fit of the surge block in the monitoring well. This higher, more aggressive, inflow helps remove fines from the sand pack. During the down stroke, the surge block causes a piston like pumping stroke forcing a higher volume of water into the valve but also pushing some water back through the screen and sand pack. The bidirectional water flow at the screen is widely recognized as the most effective method for breaking down bridging in sand packs and developing monitoring wells.

As always, a Waterra technician is available to help you choose an appropriate configuration for your application.