Unconventional gas/oil exploitation and stimulation depends strongly on the efficiency of the hydraulic fracturing (HF) treatment, via which connecting fracture networks are created and thus the conductivity for fluid flow in low-permeability reservoirs is enhanced. However, the cost related to hydraulic fracturing increases monotonically with the number of fractures. Therefore, methods to reduce the fracturing cost while still achieving the desired stimulation effect is an important factor to be considered in the hydraulic fracturing design. Although thermal effects on stress distribution and deformation have been recognized for decades, the effect of temperature change on shale gas stimulations has not receive enough attention. The injection of a cold fluid into a deep horizontal well can produce a large temperature difference between fluid and rock, for example, during the drilling of a horizontal well and later during the hydraulic fracturing of the well. This paper investigates numerically the thermal effects on the hydraulic fracture initiation and propagation for the condition of constant fluid pressure along the horizontal well by using the coupled 2D displacement discontinuity method (DDM) model, MineHF2D. In particular, the fluid pressure used is set to a value less than the required value in driving the growth of an open fracture with a finite length. And the thermal cooling induced tensile stress is needed for the fracture to extend. A comparison is carried out for the mechanical responses, such as fracture length and opening and fluid pressure, under different cooling conditions. The numerical results show that the fractures can propagate with the assistence of thermal cooling. The thermal cooling can increase the fracture aperture to facilitate fluid flow, although the fracture propagation speed is then relatively slowed down. It is aslso demonstrated that, the thermal cooling tensile stress can propagate multiple fractures and the reduction of fluid temperature in the horizontal well will reduce pressure to initiate fractures and potentially lower the cost of fracturing treatments.

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