Page 204 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Fluid-rock interactions 187

8.6 Permeability changes from water-rock
interactions

If microfractures are generated, the flow capacity near fractures may be
improved. If the fractures can be connected to form a network, then perme-
ability would be improved in a large scale. Zhang et al. (2017) and Zhang
and Sheng (2017c) measured the permeability after hydration under isotropic
compressive stress using an Autolab-1000 servo-hydraulic operated system
(New England Research Company, USA). The measurement principle is
based on a pulse decay method. The higher upstream is imposed, and the
downstream pressure is recorded. They found that the permeability was higher
using a higher KCl concentration. It implied that the hydration or swelling
caused formation damage.
Zhou et al. (2016) measured shale gas permeability during water imbibi-
tion. Although they concluded that the shale matrix permeability and fracture
permeability were reduced, the permeability reduction was actually the
reduction in the effective gas permeability. The causes of the reduction
were not supported by data, although they claimed rock swelling. But one
main reason is the increased water saturation that blocked gas flow. They
also found that shale permeability was increased if there initially existed
microfractures, because water imbibition reopened those microfractures
because of shear and tensile failure.
Behnsen and Faulkner (2011) compared the permeability of compacted
and confined phyllosilicate powders measured using argon and that using
water. The argon permeability was always higher than water permeability
(up to 1.8 orders of magnitude). They attributed the difference to the hydro-
philicity of tested minerals and hydrogen-bonding surface properties. They did
not report the generation of fractures. Moghadam and Chalaturnyk (2015) also
reported that measured gas permeability is higher than the liquid permeability.
Duan and Yang (2014) measured the permeabilities of fault rocks from the
rupture of Wenchuan earthquake using nitrogen gas and distilled water under
the confining pressure ranging from 20 to 180 MPa at a room temperature.
The water permeability was about half order smaller than the gas permeability
corrected by the Klinkenberg effect. They attributed the difference to the
reduction of effective pore size caused by the adhesion of water molecules
to clay particle surface and water-swelling of expandable clay minerals.