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Viscoelastic surfactant fracturing fluids, also known as clean fracturing fluids, have attracted extensive attention in the field of hydraulic fracturing because of their advantages, such as complete gel breaking, no residues, and low formation damage. However, the complex synthesis process, high cost, and the inability to reuse have limited the practical application of clean fracturing fluids. Herein, a pH-responsive clean fracturing fluid with pH-regulated apparent phase and rheological behaviors was constructed based on the mechanism of pseudo-trimeric surfactant and wormlike micelles formed under specific pH conditions by N,N-dimethyl oleoaminde-propylamine and tricarballylic acid. The results show that the zero-shear viscosity of the fracturing fluid can reach more than 111.2 Pa·s, and it can switch between a high-viscosity gel state and a low-viscosity aqueous solution state more than four times by adjusting pH. The constructed clean fracturing fluid is suitable for medium and low-temperature oil and gas reservoirs. The viscosity of the fracturing fluid is still higher than 500 mPa·s after shearing at 60 °C and 170 s−1 for 60 min. In addition, the fracturing fluid can be completely broken within 1 h, and the gel broken-fluid has low viscosity and no residues. [ABSTRACT FROM AUTHOR]

A method of single vertical well combined with hydraulic fracturing is proposed to prevent short circuits and enhance heat mining. The technical and economic feasibilities of geothermal energy exploitation from a deep reservoir are analyzed based on this method. A simulation model was established to analyze the coupled heat transfer between wellbore and reservoir, and then thermodynamic performances and economic analyses of single-flash, double-flash, and flash–organic Rankine cycle geothermal power generation systems were carried out. Simulation results indicate that the heat mining rate can maintain above 3 MW after 40 years of exploitation from the reservoir with 235°C using a water circulation rate of 432 m3/day. A combination of large horizontal permeability, high circulation flow rate, and excellent thermal-insulating tubings favors high heat mining. Thermodynamic cycle analyses show that the net power outputs from the single-flash, double-flash, and flash–organic Rankine cycle systems under the optimal condition are 513, 646, and 627.8 kW, respectively. Correspondingly, the geothermal power generation cost ranges from $0.086/kWh to $0.095/kWh , which is a little higher than the conventional power generation cost. Double-flash or flash–organic Rankine cycle is suggested to be installed for geothermal power generation if more electricity is needed. [ABSTRACT FROM AUTHOR]