Gas Injection phases (Highlighted in yellow)

First series of gas injections

The main gas testing began on 28 January 03 with removal of water from the injection lines. The first gas was injected on 29th Jan 03 at a rate of 0.025 mg/s (event RGI1). The injection rate was then increased in a series of steps: 05/03/03 0.05 mg/s (RGI2a); 07/05/03 0.1 mg/s (RGI2b), 17/06/03 1 mg/s (RGI3a); 25/08/03 5 mg/s (RGI3b). The gas injection was shut-in on 02/098/03 after injection of approximately of 8.5 m3 of Nitrogen. The TDRs (red) and piezometers (blue) that showed a distinct reaction to gas injection are shown below with an interpretation of the possible gas flow paths.

After gas injection the volume of free gas remaining in the silo and vent measured was measured and WT2 was performed to identify any changes in EBS performance due to the gas injections.

Second series of gas injections

A second series of gas injections using a cocktail of tracers (Helium, Isobutane, Neon, Krypton, Sulphur hexafluoride) mixed with Nitrogen was performed after WT2. Towards the end of the test H2S was added to the cocktail as part of a flow visualization experiment. The test was again arranged as a series of constant rate segments: 08/01/04 0.05 mg/s Nitrogen+tracer (RGI4a); 27/01/04 1 mg/s Nitrogen + tracer (RGI4b); 01/03/04 gas injection split 50/50 between two lines in silo (RGI4c) 03/03/04 H2S added to tracer cocktail in one injection line.

Concentration measurments at different locations

Locations of sensors that reacted during RGI4

After the second series of gas injections the free gas volume in the silo and vent was again measured and the EBS was then depressurized and dewatered prior to excavation.