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Fluid-rock interactions 211
(A) Sample A, before and after 10 day exposure to deionized water
0 d 10 d 10 d
Lamination Hydration-induced
direction fracture
10 mm
(B) Sample B, before and after 10 day exposure to 10 wt.% H SO solution
4
2
0 d 10 d 10 d
Lamination Reaction-induced
direction fracture
10 mm
(C) Sample C, before and after 10 day exposure to 10 wt.% (NH ) S O solution
4 2 2
8
0 d 10 d 10 d
Lamination
direction
Reaction-induced
fracture
10 mm
Figure 8.32 Macroscopic observations of fractures induced by (A) clay hydration and
(B) H 2 SO 4 solution and (C) by (NH 4 ) 2 S 2 O 8 solution in the unconfined shale samples
(Chen et al., 2018).
the (NH 4 ) 2 S 2 O 8 solution, suggesting that the fractures were induced by the
above reactions, and they were not affected by the organic fraction at the
experimental time scale.
Note that from the first of the above three reaction equations, pyrite reacts
with ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) to produce the acid solution of
þ
2
H þ SO : In an anoxic depositional environment, pyrite commonly exists
4
in a shale formation. Even if there is no pyrite, a sulfate-bearing acid solution
like H 2 SO 4 can react with carbonate minerals to precipitate gypsum, and the
above volume increase-induced fractures should be created. However,
the above experiments were conducted without confinement.