This paper details the study of a new fracturing fluid that is based on a supramolecular complex between associative polymer and viscoelastic surfactant (VES). The crosslinked complex gel was based on weak physical attractive forces, such as van der Waals, hydrogen bonding, and electrostatic interaction between associative polymer and wormlike micelles of VES. The concentration of surfactant in the new fluid is 10 times less than that of VES fracturing fluid. The combination of VES and associative polymer synergistically enhances the viscosity to several times more than that of the individual components alone. The fluid system was optimized by experimental design. The microstructure of wormlike micelles and complex formation was verified by electron microscopy. The fluid is shear stable at high temperature for 1 hour. The dynamic rheological properties of the supramoleulcar fluid show high viscoelasticity, in which the elastic moduli are higher than the loss moduli below an angular frequency of 0.1 rad/s. The proppant-transport test in a large-scale fracture simulator showed good proppant-suspension ability. The fluid has 50% lower formation damage than conventional guar. The fluid was prepared with fewer additives, formed gel instantly, and can be mixed on the fly in the field. The gel can be completely broken with almost no residue. Field application of the new fracturing fluid in a gas well showed the enhancement of gas production by more than 100%. The fluid has 20% lower friction pressure than guar fluid. Hence, the new supramolecular fluid is an effective fracturing fluid.
The multifracture competitive growth from a horizontal well is an essential issue in multi-cluster fracturing design. In recent years, extremely limited entry (ELE) fracturing has been implemented to promote uniform multifracture growth. However, the mechanism of multifracture growth and ELE design remain unclear. Based on the planar three-dimensional multifracture propagation model, a multi-cluster horizontal well fracturing model that considers ELE design has been developed. The model considers flow in the wellbore and fluid filtration loss in the fracture. The simulator enables the simulation and analysis of non-uniform in situ stress, filtration loss, and fracture properties. Using this program, we simulated the propagation process of multiple clusters of fractures in ELE fracturing of horizontal wells. The results show the following: The perforation friction in the ELE fracturing can counteract the difference in fluid allocation caused by stress interference, allowing all clusters of perforations to have even fluid allocation but to differ significantly in fracture geometry. The in situ stress profile and 3D fracture stress interference determine the fracture geometry, and the fracture of the middle cluster could cross through the layer with relatively higher in situ stress, resulting in a decrease in effective fracture area in the pay zone. Furthermore, an increase in perforation diameter causes the flow-limiting effect of the perforations to decrease. The fluid volumes entering different clusters of perforations become less uniform. The difference in fracture toughness within a perforated stage has a minor influence on the fluid allocation between different clusters, while the in situ stress distribution within a perforated stage has a significant impact on the fluid allocation between different perforation clusters in the stage. Fractures preferentially propagate at the perforation points with lower in situ stress and stress interference. This study can be helpful to understand multifracture competitive growth and the optimization of ELE fracturing design.
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