shale and the effect of hydration on
shale before hydraulic fracturing. 1-6
The authors of this article used
fresh water to soak shale core samples
for spontaneous imbibition in lab experiments and injected stream water
into pilot wells.
Experimental samples were divided
into three levels of pore-fracture development: not developed, better
developed, and best developed. Researchers found the shale cores having better-developed primary pores
and natural fractures were strongly
affected by hydration, while hydration had the weakest effect on cores
with the best-developed pores but no
Fig. 1 shows hydration increased
connectivity between pore throats
and fractures by 65% in Sample A,
inducing more fracture branches.
Fig. 2 shows fracture width increased as primary fractures propagated along the bedding plane.
The hydration effect’s intensity
partially depends on how long the
Longmaxi shale was hydrated.
Researchers ran laboratory experiments both under atmospheric
conditions and under a confining
pressure of 10 MPa. Samples were in-
HYDRATION PILOTS Table 1
Initial pumping Maximum pumping rate, injection, Shut-in duration
Well Pilot Stage rate, cu m/min cu m/min cu m for hydration, hr
A 15 2.0 5. 8 200 12
18 2.0 5. 8 300 12
B 8 0.5 3. 5 300 14
18 0.5 3. 8 300 13
PRESSURE CURVES, EARLY HYDRAULIC FRACTURING* Table 2
Abrupt pressure drop throughout Vector scan
Well Stage Hydration Curve shape drops, number fracturing, MPa distribution
A 14 No Straightline 1 2 Absent
15 Yes Multipledrops 2 26 Absent
18 Yes Multipledrops 3 17 Absent
19 No Straightline 1 8 Absent
B 7 No Straightline 1 2 Centralized
8 Yes Serrated curve Many small 13 Fragmented
17 No Straightline 1 0.5 Centralized
18 Yes Serrated curve Many small 1 Fragmented
CT scans of reconstruction of shale samples from Well A before hydration (left) and
after hydration (right) (Fig. 3).
CT images of Well B shale sample before hydration (left) and after hydration (right) (Fig.