This document summarizes research on the origin and distribution of hydrocarbons in salt domes. Some key findings include: - Hydrocarbons are naturally occurring in salt rocks but are heterogeneously distributed in localized streaks and clouds. - They are only found along grain boundaries, healed fractures, or within anhydrite capillaries connected to boundaries. - Their origin is both intrasaline (naturally occurring within the salt) and from external source sediments like the Stassfurt carbonate. - Deformation experiments on salt rocks show that fluids are confined to very limited zones and do not interconnect through the rock, indicating salt is hydraulically tight outside zones of extensive deformation.

1. 1
Origin and microdistribution of fluids in salt
domes
Jörg Hammer, Gernold Zulauf
Federal Institute for Geosciences and Natural
Resources (BGR) & University Frankfurt/Main
Washington, DC
September 7-9, 2016

2. 2
Distribution of hydrocarbons (excavations and
boreholes, crosscut 1 east)

3. 3
Rare local streaks and clouds of hydrocarbons at Gorleben
exploration mine
N

4. 4
Rare local streaks and clouds of hydrocarbons at Gorleben
exploration mine
Large condensate patch in crosscut 1 west (eastern wall, 840 m-
level)
Q1W Q1W
02YEQ02/RB648
02YEQ02/RB778
Flashlight photo UV-photo

5. 5
content of hydrocarbons (crosscut 1 west)

6. 6
Hydrocarbons in drillings at Gorleben exploration mine
Crosscut 1 West
Displayed concentration of hydrocarbons = 401 CC 
>50 mg/kg
< 1 mg/kg_
> 1 < 5 mg/kg_
> 5 < 50 mg/kg_

7. 7
Hydrocarbons at grain boundaries (z2HS1; “Knäuelsalz“)
100 µm
100 µm
100 µm
50 µm

8. 8
Hydrocarbons at grain boundaries (z2HS1; “Knäuelsalz“)
100 µm
100 µm
Z = 480µm
Z = 400µm Z = 115µm

9. 9
HC in anhydrite in halite rocks (z2HS1; “Knäuelsalz“)
100 µm200 µm
20 µm 50 µm
LAS AF:
AOTF = 458nm, 496nm, 633nm
z = 20,14 µm
UV-Mic.
LEITZ-Filter D
BP 355 nm to 425 nm; LP 460 nm
Z = 5µm

10. 10
Key messages from HC studies in German salt diapirs
• hydrocarbons are a natural occuring component of salt rocks
• the distribution of the hydrocarbons within Gorleben salt is highly
heterogeneus and only of local character (isolated streaks, clouds)
• the hydrocarbons occur only along grain boundaries, healed
(respectivly technical caused open) fissures or within capillaries of
anhydrite with contact to grain boundaries
• HC occur always together with intrasalinar brines
• the origin of hydrocarbons (hc) is intrasalinary (autochthone hc) and
from external sediments (allochthone hc)
• organo-geochemical investigation of the hydrocarbons point to the
Stassfurt carbonate (z2SK) as source rock

11. 11
Stassfurt carbonate (z2SK) as source rocks of HC

12. 12
Stassfurt carbonate (z2SK) as source rocks of HC

13. 13
The material tested vs. natural halite rocks
Table salt: Grain sizes: 200 – 400
µm, Composition: analytical grade
halite (99.9% pure)
For each experiment, about 150 mg of
halite and 7-15 mg of distilled water
used
 7 – 16 Vol.-% = brine filled
porosity of the condensed
material
Natural rock salt (z2HS, Gorleben)
polygonal and lobate halite grains
Grain sizes: < 1 mm ... 10 mm
Composition: > 90% Halite, anhydrite,
polyhalite
 Water content lower 1 wt.-%
 The grain scale, grain shape and the water
content is not realistic in experiments/modeling

14. 14
Halite rocks, Morsleben: microfabrics
Foliation in
halite, caused
by a moderate
grain-shape
fabric
Euhedral crystals
replacing
subhedral halite
crystals
Subgrains in
halite
Mertineit et al. (2015)

15. 15
Halite grain sizes and axial ratios of z2HS1 and z2HS2 samples
Gorleben, 840 m-level
Thiemeyer et al. (2016)

16. 16
3D visualisation of fluid-filled porosity
Computertomography: visualisation of Ct-analyses by using VGStudio
Thiemeyer et al. (2015)

17. 17
Hydrocarbons at grain boundaries (z2HS1; “Knäuelsalz“)
200 µm

18. 18
T = 345 °C
ė = 10-7 s-1
eX = 120%
σ1-σ3 (max) = 4,6 MPa

19. 19

20. 20
1 mm
Hi = 1.5 mm
X
Y=Z
Y=Z

21. 21
Boudinage of anhydrite. Note, the fluids are found only in a very limited
zone around the anhydrite layer.

22. 22
Postkinematic discharge of fluids from anhydrite into halite in
experimentally deformed sample
Halite
Anhydrite

23. 23
Conclusions from deformation experiments
• Halite was deformed in the viscous deformation
regime
• The major deformation mechanisms in halite are
solution-precipitation processes (fluid-assisted grain-
boundary-migration recrystallization) and dislocation
creep with subgrain formation
• During thermomechanical experiments fluids on
halite grain boundaries do not interconnect
• Halite rocks out of the EDZ are hydraulically tight.