1. Hydraulic stimulation in the light of tracer tests
The topic announced read „Hydraulic stimulation in the light of…“,
but here I want to make another point:
understanding the properties of TRACERS themselves is crucial to the interpretation:
some comments on tracer tests results and the presuppositions of their interpretation
I. Ghergut
University of Göttingen Geothermics Group (Prof. Martin Sauter)

2. (Deep Continental Drilling, Germany) t. t
(Deep Continental Drilling, Germany) t.t.: depleted, stimulated, post-stimulation state
1 - year injection
1 - year production
1 - year production
At the KTB site: tracer tests were conducted in DIFFERENT hydraulic regimes;
and each test uses SEVERAL tracers,
and we want them to yield DIFFERENT signals which we can interpret consistently.

3. tracer 1: values in this range tracer 2: values in this range
(Deep Continental Drilling, Germany) use different tracers, and rely on them!
For instance, we were so smart to arrange for QUALITATIVELY different signals,
by tailoring the injected tracer MASS RATIOS in SUCCESSIVE slugs;
But whether this indeed works
depends on the tracers being physicochemically CONSERVATIVE.
tracer 1: values in this range
tracer 2: values in this range

4. (Deep Continental Drilling, Germany) interpretation is only as good as the assumptions made on tracer behaviour!
… and our glorious interpretation based on these different tracer signals IS ONLY AS GOOD as the assumptions made.
- We ASSUME a lot; but we KNOW very little!

5. (Hydro-frac tracing in 4-km deep sedimentary) 2 organic tracers, very different behaviour!
Now another tracer application, in a sedimentary reservoir: using 2 different organic tracers which we didn‘t want to behave TOO differently.
We wanted the difference in their signals to be due to different MOLECULAR DIFFUSION only. But, obviously, this was NOT the case!

6. long-term, moderate-rate
(GroßSchönebeck: multi-tracer tests, forthcoming) want to be able to rely on various organic tracers!
short-term, high-rate
long-term, moderate-rate
In the forthcoming tracings in GroßSchö., we want to be able to RELY on various ORGANIC tracers.
About these tracers, we ASSUME a lot, but (for the time being) KNOW very little…

7. spend more effort to: improve tracer analytics in saturated brine
understand physicochemical behaviour of tracers in situ
CONCLUSION: more effort will need to be spent on
Improving tracer analytics in saturated brine
Understanding physicochemical tracer interactions with the in-situ transport milieu
University of Göttingen Geothermics Group (Prof. Martin Sauter)