Borehole
Gas Analysis
A borehole is basically a thin shaft that
extends into the ground vertically or horizontally. There are numerous purposes
for drilling boreholes including water, petroleum, or gas extraction. A
borehole may be required for environmental or geological investigations.
We have had numerous requests in the past
from mining companies who want to test the gas atmosphere in boreholes
extending vertically into the ground. The site may be a prospective mine, a depleted
mine, or a critical area of interest near the mine. A portable instrument is required because there may be several boreholes on a site. The technician travels to each hole to obtain a series of gas analysis readings.
For gas analysis, there will usually be a
tube bundle extending to different depths into the shaft. By attaching a gas analyzer
to each of the tubes, an atmosphere vs. depth profile can be obtained of the shaft.
This information can be indicative of soil condition, microbial activity, or
some other investigated parameter.
We have frequently sold the Model 309
Portable O2 / CO2 analyzer for this application. Because some of the samples
will be pulled up from deep into the borehole, we can install a heavy duty pump
into the instrument. We usually incorporate a bowl filter of some kind at the
sample inlet to capture any water that may come up with the gas.
In some cases, analysis might be required
for a rock or ore sample that is brought to the surface for study. Because gas
does not normally come off of a rock sample in large constant volumes, the
sample will be sealed into a canister.
Inlet and outlet ports on the canister allow
the gas analyzer to be connected via flexible tubing. The outlet port on the canister
is connected to the inlet port of the analyzer. The inlet port of the canister is
connected to the vent of the analyzer. The gas flows in a closed loop as shown
in the picture below.
Valves and tubing can be arranged to minimize the amount of diluting air that is introduced into the canister atmosphere.
Valves and tubing can be arranged to minimize the amount of diluting air that is introduced into the canister atmosphere.
Ground
Level Gas Analysis
We have also had requests for analyzers for
ground level gas analysis. The procedure may consist of a domed and sealed
cover over a section of soil. The cover has a tube fitting which may be
connected to a gas analyzer.
The gas analyzer will pull a sample from
the airspace between the cover and the soil. Because a limited volume of air
exists between the cover and the soil, a pressure reduction will develop as the
analyzer pulls more sample. The heavy duty pump can continue to pull so that a
small sample of soil gas can eventually be obtained. We suspect that these conditions of sample extraction are not ideal for high accuracy readings. However, some users have reported
that the resulting readings are enough to satisfy the requirements of their soil investigations.
Other interesting links:
NOVA Analytical Systems
1-800-295-3771
sales at nova-gas dot com
websales at nova-gas dot com
http://www.nova-gas.com/
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