Transcript Evaluation of common hydrological tracers in porous media

Evaluation of common hydrological
tracers in porous media
P R ATHA P MOOL A
BE RG UR S I G FÚSSON, A N DR I ST EFÁNSSON
Research motivation
The aim is to study water-rock
interaction and H2S mineralization in
porous media
One effect of mineralization is the
change in porosity
Tracer tests can be used to study the
in situ porosity changes
http://karst.iah.org/karst_hydrogeology.html
Why tracer tests?
To study the groundwater flow path
from injection well to monitoring well
in aqueous systems with the aid of
recovery upon time
 To examine the characteristic
behavior of the subsurface layers and
to calculate effective porosity
http://www.waterencyclopedia.com/St-Ts/Tracers-in-Fresh-Water.html
What is an “ideal“ tracer?
An ideal tracer:
 Should have a low detection limit
 Should not react chemically or be
absorbed
 Should be easily available and
inexpensive
http://www.zaraenvironmental.com/geology/
Experimental tracer tests
The chemical behavior and reactivity of some tracers were studied in the
laboratory
Laboratory experiments have similar setup as tracer tests in nature
Tracer
Injection
point
Injection well
Teflon column
Sampling
point
Ground water system
Monitoring well
Tracers
6 common geohydrological
tracers were studied
Amino G acid
Amino Rhodamine G
Fluorescein sodium salt
Napthionic acid
Pyranine
Rhodamine B
Amino G Acid
Pyranine
Amino Rhodamine G Fluorescein söddum
Nap thionic acid
Rhodamine B
Experimental setup
Flow-through column
experiments were conducted at
room temperature
The teflon column was preloaded
with rock
The tracer was injected and the
recovery monitored at the outlet
PTFE column
Tracer
Blank
Pump
Spectrophotometer
Experimental setup
Various conditions
pH = 3, 6.5 &9
PTFE column
Tracer
Blank
Basaltic glass, rhyolite and
quartz(45-125µm)
Pump
Spectrophotometer
How is pore volume measured with the
help of breakthrough curves?
1.2
1.0
Non reactive tracer
c/c0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
Number of porevolumes
20
Results
Three types of tracer trends were observed :
Type 1 – always non-reactive in all studied rock types and pH (100% recovery)
Type 2 – always reactive in all studied rock types and pH (70-90% recovery)
Type 3 – sometimes reactive, sometimes non-reactive depending on rock type
and pH
What does it mean?
Some common hydrological tracers react upon water-rock interaction
BUT
an ideal tracer should NOT REACT chemically or be absorbed!
Next steps
Water-rock interaction involves rock dissolution followed by
secondary mineral formation
This process may result in a decrease in porosity as the minerals
formed occupy more space than the minerals dissolved
Recent experiments of H2S mineralization demonstrate this (talk
by Snorri Guðbrandsson)
Pore volume changes upon H2S
mineralization
The water-rock interaction and H2S
mineralization in porous media are
currently being studied in our group
Outlet
It is planned to follow the
mineralization as a function of time
using laboratory tracer tests to
measure the pore volume changes
Reactor
Sampling
point
Intlet
Thank you
for your attention