Abstract：
The volume fracturing technique is one of the key methods of shale gas development. It, can cause the problems of
casing deformation while facilitating shale gas development. The main reasons for the casing deformation are fault activation
and interface slippage induced by hydraulic fracturing. Firstly, this paper explains the mechanism of fault activation induced by
hydraulic fracturing by analyzing the different modes of fracturing fluid entering the fault, which provides a theoretical basis for
analyzing the influence of fault activation on casing deformation. Secondly, a new model considering the shear deformation of
casing caused by fault activation and interrupted layer slippage during the hydraulic fracturing is established. The model innova
tively considers casing loading history within the full life cycle of wells, including drilling, casing running, cementing, cement
slurry hardening, hydraulic fracturing, production, and injection. Finally, a parametric study is performed to determine the effects
of fracturing fluid pressure, fault dip, fracture length, casing thickness, and cement sheath property on shear deformation of
casing. The results show that fault sliding will produce a shear force acting on the casing system which will result in a reduction
in the casing diameter. Eventually, it may lead to the shear failure of the casing. As the length of the fault increases, the degree of
casing shear deformation also increases. When the length of the fault is 80m, the shrinkage of the casing reaches 11.95 mm. With
a continuous increase of fracturing fluid pressure, the degree of shear deformation of the casing also increases. When the fluid
pressure is 80 MPa, the maximum casing diameter reduction reaches 9.94mm. When the fault dip is about 30°, the casing diame
ter shrinks the most, up to 9.53 mm. However, increasing the casing thickness and the elastic modulus of the cement sheath does
not significantly improve the shrinkage of the casing. Therefore, well trajectory should be prevented from crossing large faults
during well structure designing, and large-scale fault areas should be avoided during hydraulic fracturing design. Meanwhile, the
pumping speed of fracturing fluid should be reasonably designed to keep it as low as possible to reduce fluid pressure. This work
is helpful for understanding the mechanism of shear deformation of casings induced by fault activation and interrupted layer
slippage during multi-stage hydraulic fracturing in shale gas, which also provides guidance for engineering operations.
