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Understanding the reorientation mechanism of near-wellbore hydraulic fractures is very important for optimizing parameters in field fracturing treatments. In this study, a fully 2D coupled seepage–stress model based on the extended finite element method (XFEM) model is applied to investigate the fracture trajectory and reorientation. The numerical model considering pore pressure is verified by a true triaxial laboratory experiment. The results show that the fracture is generally initiated from perforation and rotates to the direction of maximum horizontal stress with different curving distances. The fracture trajectory and reorientation distance can be influenced by the rock mechanics and fracturing application parameters, including elasticity modulus, Poisson's ratio, tensile strength, perforation angle, horizontal stress difference, and injection rate. More exact behavior of fracture propagation can be described according to the parametric study. The results provided in this paper can be clearer in the prediction of the fracture trajectory and fracturing design in the near-wellbore region. [ABSTRACT FROM AUTHOR]

The cofferdam of the tidal flats behind Changxing Island was studied to explore the seepage–stress coupling properties of the cofferdam on a soft clay foundation under a storm surge attack. A numerical model coupling multiple influencing factors was established, which included tidal changes, wave loading, surges, soil strength degradation, and seepage effects. In addition, the dam global stability was investigated. The results showed that the permeability coefficient of the dam determined the magnitude and distribution of the seepage field during tidal level fluctuations. The tidal flood and ebb changed the periodic displacement of the dam body. When accounting for the wave loading applied on the cofferdam, the strength-weakening effect of the soil foundation induced by the wave cyclic load could produce additional displacement in the static and dynamic analysis of the dam. A stress-concentrated area was evident at the slope foot and hillslope in the coupled-field dam model that included the seepage force. The influence factors played important roles on the stress field, displacement field, and global stability. By comparing the calculated results and data, the established model and calculation method were validated, and the results are of theoretical and practical interest for predicting cofferdam resistance to storm surges. [ABSTRACT FROM AUTHOR]

Refracturing is a key technology in enhancing the conductivity of fractures from hydraulically-fractured wells. However, the deflecting mechanism of the diverting fracture is still unclear. In this paper, a fully coupled seepage-stress model based on the extended finite element method (XFEM) was developed to realize the deflection mechanism of the refracturing fractures. The modified construction of refracturing was then verified by laboratory experiments. Furthermore, two new deflection angles considering the influence area along initial fracture length were introduced to evaluate the refracturing. The numerical results demonstrated that: (1) lower stress difference, larger perforation angle and longer perforation depth can lead to a higher deflection angle, thereby a more curving propagation path of the diverting fracture; (2) increasing injection rate or fluid viscosity can significantly enhance the diverting behavior; and (3) an initial location near the root of the initial fracture results in a larger value of the deflection angle, which is preferred for far-field refracturing. The conclusions in this study can be a systematic guide for the parameter optimization in refracturing treatment. [ABSTRACT FROM AUTHOR]