Horizontal well fracturing technology
is widely used in the development
of shale gas resources. After the fracturing operations, natural and
artificial fractures exist in the reservoir at the same time, which
has significant effects on spontaneous imbibition to increase shale
gas production. Based on nuclear magnetic resonance technology, this
work studies the spontaneous imbibition property of fractured shale,
including artificial and natural fractures, surface cemented minerals,
boundary conditions, etc. The results show that the relaxation time
spectra reflect the characteristics of water and gas migration in
the rock pore space. The micropores and the small pores are the main
storage space for water in shale. After water imbibition starts, the
imbibition volume is roughly proportional to the square root of time.
Through the comparative experiments on artificial fractures, natural
fractures, and seamless cores, it is found that the existence of fractures
can significantly promote water imbibition, and the imbibition speed
of artificial fractured cores is faster than those of others. Because
of the existence of artificial and natural fractures, the number of
pores for gas discharge increases, and the imbibed volume is slightly
more. When the cemented minerals such as quartzite and calcite are
attached to the core surface, they have poor water sensitivity and
block some of the pores, thus resulting in a slower imbibition speed.
Different boundary conditions will not only affect the contact area
between the core and water but also influence the types of imbibition,
which changes the water flow path and imbibition speed. This study
provides an important insight into spontaneous imbibition in gas shale
after the fracturing operations.