Multistaged temporary plugging fracturing in horizontal wells is an emerging technology to promote uniform fracture propagation in tight reservoirs by injecting ball sealers to plug higher-flux perforations. The seating mechanism and transportation of ball sealers remain poorly understood. In this paper, the sensitivities of the ball sealer density, casing injection rate and perforation angle to the seating behaviors are studied. In a vertical wellbore section, a ball sealer accelerates very fast at the beginning of the dropping and reaches a stable state within a few seconds. The terminal velocity of a non-buoyant ball is greater than the fluid velocity, while the terminal velocity of a buoyant ball is less than the fluid velocity. In the horizontal wellbore section, the terminal velocity of a non-buoyant or buoyant ball is less than the fracturing fluid flowing velocity. The ball sealer density is a more critical parameter than the casing injection rate when a ball sealer diverts to a perforation hole. The casing injection rate is a more critical parameter than the ball sealer density when a ball sealer seats on a perforation hole. A buoyant ball sealer associated with a high injection rate of fracturing fluid is highly recommended to improve the seating efficiency.

Hydraulic fracturing has been proven to be an effective technique for stimulating petroleum reservoirs. During the hydraulic fracturing process, the effects of the natural fracture, perforation orientation, stress reorientation, etc. lead to the production of a non-planar, mixed-mode I/II hydraulic fracture. In this paper, a criterion for a mixed-mode I/II hydraulic fracture crossing a natural fracture was first proposed based on the stress field around the hydraulic and natural fractures. When the compound degree (K_II/K_I) approaches zero, this criterion can be simplified to identify a pure mode I hydraulic fracture crossing a natural fracture. A series of true triaxial fracturing tests were conducted to investigate the influences of natural fracture occurrence and in situ stress on hydraulic fracture propagation. These experimental results agree with the predictions of the proposed criterion.

Hydraulic fracturing is the core technology for stimulating unconventional oil-gas reservoirs. The effective placement of proppant is directly linked to the success of the fracturing operation and reservoir productivity. In-depth investigations into the migration and settling behavior of proppant can provide a scientific foundation for optimizing fracturing parameters and fracture conductivity. Numerical simulations were employed to analyze the effects of many factors, such as the fracturing fluid velocity and viscosity, proppant size and density, and fracture surface roughness and injection position, on proppant migration within a planar fracture. Some interesting findings are: ① As the fracturing fluid velocity increases, the maximum height of the sand dune initially increases and then decreases, whereas the horizontal distance between the highest point of the sand dune and the entrance increases. ② Excessively high fracturing fluid viscosity results in a significant portion of the proppant remaining suspended within the fracturing fluid, thereby reducing the settling velocity and causing proppant to travel further. ③ Smaller proppant particles exhibit longer migration distances, making them more likely to travel further before settlement. ④ Proppant with lower densities exhibit superior transportability, with a larger proportion of the proppant remaining suspended in the fluid, resulting in more efficient fracture filling. ⑤ As the roughness of the fracture surface increases, the maximum height of the sand dune also increases, and fractures with rougher surfaces exhibit a greater sand dune area. ⑥ As the injection position decreases, the maximum height of the sand dune increases and then decreases.

Intensive-stage fracturing in horizontal wells is a potentially new technology for reservoir stimulations of deep shale oil and gas. Due to a strong stress interaction among the dense fractures, the fracture geometry and stress field are very complicated, which are the bottlenecks of this technology. Aiming at simulating the intensive-stage fracturing, a coupled three-dimensional (3D) fracture model of multiple-fracture simultaneous propagation is proposed. The dynamic behavior of the fracture propagation and stress field was analyzed using this model. The perforation parameters were optimized for improving the fracture geometry equilibrium. The results showed that the exterior fractures of the multiple fractures penetrated by the horizontal well become the main fractures, while the interior fractures are drastically restrained. The exterior fracture widths increased with increasing injection time, while the interior fracture widths decreased with increasing injection time. An extruded region was created among the multiple fractures, which restrained the propagation of the interior fractures. Only increasing the perforation cluster number did not improve the fracture geometry equilibrium in the intensive-stage fracturing. To improve the fracture geometry equilibrium, we suggest designing more perforation numbers in each perforation cluster and ensuring that both the perforation number and diameter in the interior perforation cluster are greater than those of the exterior ones.