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In order to study the effects of different parameters in hydraulic fracturing on formation temperature after low-temperature fracturing fluid is injected into high-temperature reservoir, in this paper, considering (1) osmotic pressure and capillary pressure (2) microthermal effect (heat conduction, heat convection, heat expansion, viscous dissipation) (3) the coupling processes of temperature (T), hydraulic, (H) mechanical (M) and chemical (C) in hydraulic fracturing process, and the coupled temperature prediction model of oil-water two-phase THMC based on discrete fractures is established. The effects of fracturing fluid temperature, reservoir temperature, dimensionless conductivity, Young's modulus, injection rate, cluster spacing, and proportion of branch fracture area on reservoir and fracture temperature during the pumping and shut-in stages of shale oil reservoir were studied. The results show (1) For formations with different reservoir temperatures, the temperature drop at the fracture was approximately 97% from the start of the operation to the end of the 30-day shut-in. The saturation change caused by fracturing fluid filtration is much larger than the temperature change caused by heat transfer, and it is found that the temperature and saturation change mainly occur in the early shut-in period (2) Imbibition accelerates the filtration loss of fracturing fluid. During pumping, the bottom hole temperature with imbibition considered is lower than that without imbibition considered. The temperature curve with imbibition considered begins to deviate about 10 min after pumping, but the final temperature tends to be the same, (3) When the fracturing fluid is pumped at high pressure, the fracture and matrix will be deformed, which will improve the porosity and permeability of the near well zone, thus speeding up the heat transfer rate. The high Young's modulus inhibits the increase of permeability. Compared with the young's modulus of 40 GPa and 20 GPa, the increase of permeability decreases by 9% (4) When the well was shut in for 30 days, the cluster spacing was greater than 20 m, and the temperature change around the fracture did not affect the clusters on both sides. The spacing between the clusters was 5 m, and the perforation clusters on both sides had a significant effect on the temperature. The temperature of the reservoir between the two adjacent clusters dropped from 393 K to 385 K. When there is a branch fracture, the small cluster spacing is equivalent to increasing the complexity of the fracture and accelerating the initial heat transfer rate. (5) High injection temperature, high dimensionless conductivity, low Young's modulus and low pumping rate are conducive to the heat transfer of fracturing fluid in the formation. • Based on the discrete fracture model, the temperature prediction model of oil-water two-phase flow was established. Considering the capillary force and osmotic pressure, the temperature (T) -hydraulic (H) -mechanical (M) -chemical (C) was realized. The finite element method is used to solve the model. • The effects of multiple factors on reservoir and fracture temperature during fracturing pumping and shut-in stages are analyzed. [ABSTRACT FROM AUTHOR]

To understand the fracture behavior for variable density in-plane perforations on a horizontal well, true triaxial hydraulic fracturing experiments were performed with acoustic emission monitoring. The experimental results indicate that the variable density in-plane perforations can not only create transverse fractures but also arrest fracture propagation toward undesirable zones. The in situ stress and treatment parameters play significant roles in the fracture morphology and breakdown pressure. Under a large horizontal principal stress difference, there is a high possibility for simple transverse fracture creation, which results in a lower breakdown pressure. Moreover, the decrease in fracturing fluid viscosity can increase the fracture complexity and increase in pump rate can increase breakdown pressure and induce the complex fracture geomtetry. The acoustic emission (AE) characteristics and cutting fracture morphology demonstrate that not all perforations can be successfully initiated during the fracturing process. Because of the stress interaction from side perforations, fracture initiation and propagation from the middle perforation are strongly suppressed. Although the middle fracture is not fully initiated and propagated, it is still beneficial for the side hydraulic fracture connection and propagation in one plane. Secondary and axial fractures can still be observed, primarily due to the stress interaction between neighboring perforations and misalignment of the perforation tunnel orientation with the principal stress direction. In addition, the creation of complex fractures tends to occur using a high pump rate, which relates to tense fluid distribution competition from each perforation tunnel. Fracture initiation may follow an order but mostly tends to initiate from side perforations. Because of the stress interaction, hydraulic fractures from the side perforation can sometimes deviate from the perforation tunnel direction, twist and kink, and finally, generate nonplanar fractures. A large horizontal principal stress difference is recommended and beneficial for simple, straight and planar fracture creation during hydraulic fracturing stimulation with variable density in-plane completion for the horizontal well. • The application of local in-plane perforations can control the fracture path and complexity. • Tri-axial fracturing experiments were conducted on tight rock samples with local in-plane perforations. • The change in fracturing fluid viscosity and pump rate can alter the fracture path between perforations. • The connectivity of neighboring fractures can lower the breakdown pressure. [ABSTRACT FROM AUTHOR]