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206 Enhanced Oil Recovery in Shale and Tight Reservoirs

Time Rock failure indicator

1 month

HB: –0.01 0 0.01
Hydraulic fracture
200
Along horizontal well, ft 100

0

0 Hydraulic fracture 200 300 400 500 600
100
1 year Along hydraulic fracture, ft
Hydraulic fracture
200
Along horizontal well, ft 100

0

0 Hydraulic fracture 200 300 400 500 600
100
Along hydraulic fracture, ft

Figure 8.28 Likely rock failure sites 1 month and 1 year after cold water injection
(Fakcharoenphol et al., 2013).

precipitate calcite or aragonite (CaCO 3 ), (2) dissolved periclase (MgO) and
CO 2 to precipitate magnesite (MgCO 3 ), (3) Na 2 O and HCl to precipitate
salt (NaCl); or Na 2 O and SO 4 to precipitate a range of sodium sulfate salts.
Sometimes, dehydration reactions occur. Large volume changes in the rock
formation result in cracking and fracturing of the rock formation.
Chen et al. (2017) reported that oxidative reagents, such as sodium hypo-
chlorite (NaOCl), hydrogen peroxide (H 2 O 2 ), and sodium peroxydisulfate
(Na 2 S 2 O 8 ), had been widely applied in the removal of organic matter;
undoubtedly, H 2 O 2 was the most widely used oxidant to organic matter
because of its high removal efficiency and relatively low price. They used
15 wt.% H 2 O 2 to investigate the oxidative dissolution of organic-rich shale
and its effect on pore structure.