Single Packer Systems
The use of a single packer and transducer to monitor pressure at the base of a borehole is a useful option for short term measurements. If the installation has to become permanent then it is usually desirable to cement grout on to the top of the packer.
In this case Sigra can supply a multiple packer and transducer system that can be installed in the well. This ability comes from Sigra’s capability to manufacture packers, and electronics. Sometimes it is most convenient to monitor pressures in a cased, cemented and perforated casing. This would most likely be the case when the well is intended to be brought into production in the future but in the first instance can be used for monitoring.
Aquifer Monitoring Using Cement Displacement and a High Level Packer
Sigra was asked to provide a system to monitor the pressure in a 1600 m deep aquifer over a period of some decades and to be able to guarantee the accuracy of the measurement over that period to 20 mm water head.
This equates to a guaranteed accuracy of 12 ppm. As the aquifer was supposed to be relatively invariant in pressure the solution devised. This involved attaching a capillary tube with a larger pipe upper section to a cement grout (tremmie) pipe and to cement the hole. Then using the cement displacement technique a zone between the tip of the capillary tube and the aquifer was cleared by water injection and the cement allowed to set.
The system could then be tested for connectivity between the aquifer and the capillary tube tip by injecting a small volume of water and watching the pressure decay. A small diameter packer with a precision low pressure transducer could then lowered to below the water surface within the pipe and set for monitoring to continue.
The packer and transducer of this system can be removed in the event of failure or for recalibration.
This is a simple but effective system.