Re-fracturing diverting has been planned in the well Zheng-x in Zhengzhuang CBM gas field with fuzzy ball temporary plugging fluid. This job was to be done in an effort to increase the gas production by generating new fractures in the reservoir formations, without disturbing the production of the existing fractures. In laboratory studies, a fuzzy ball fluid was used to temporarily plug the artificial fractures on a 33 mm (diameter) coal plug, then an activated water was used to test the pressure bearing of the temporary plugging; it was 20 MPa, exceeding the fracturing pressure of the formation, which is 18 MPa. The percent recovery of the permeability of the coal plug previously flushed with the fuzzy ball fluid was 85%, satisfying the needs for the production of the existing fractures. In field applications, a fracturing blender truck and a water tank were used for the circulation of the fracturing fluid. A fuzzy ball fluid, with density between 0.94 g/cm³ and 0.98 g/cm³, apparent viscosity between 30 mPa·s and 34 mPa·s, was prepared through a shear funnel. After checking the existence of fractures with activated water, 60 m³ of fuzzy ball fluid was injected into the formation at 3.0-3.5 m³/h. The tubing pressure was stabilized at 12 MPa while stopping pumping for 30 min, indicating that the plugging of existing fractures with the fuzzy ball fluid was successful. The formation was then fractured with activated water when the tubing pressure was increased to 18 MPa. The azimuth of the new fractures was N13°W, as measured with microseism, meaning that 55° of diverting was realized compared with the N42°E azimuth of the existing fractures. A gas production of 200 m³ in 2 h after fracturing was achieved, doubling the gas production rate before the fracturing job. Microseism monitoring and the gas production rates before and after the fracturing job indicated that the fuzzy ball forced the fracturing fluid to divert to generate new fractures, while the production of the existing fractures was not affected. This technology is suitable for the re-fracturing of old CBM wells to generate new fractures, while the production of the existing fractures was not affected. This technology is suitable for the re-fracturing of old CBM wells.

The quality of water from the backflow fluid of guar gum fracturing fluids is determined through analyses of the backflow fluid from multiple wells. The effects of pH, reducing ions, hardness, salinity, oil contents and contents suspended matters on the performance of the guar gum fracturing fluids were studied based on the aforesaid analyses. To recycle the backflow fluid, the water quality should be controlled as follows:pH between 6.5 and 7.5, Fe²⁺ less than 5 mg/L, S²⁺ less than 2 mg/L, Ca²⁺ less than 500 mg/L, salinity less than 100,000 mg/L, and suspended matter less than 300 mg/L. These data provide a basis for the recycling of the backflow fluids of fracturing fluids.

A hydrophobically associating quadripolymer, AAMS-1, was synthesized through reverse emulsion polymerization, using AM, AMPS, hydrophobic monomer M (2-Dimethyl hexadecaneaminomethacrylate chloride)/rigid monomer S (4-acrolylamino sodium benzenesulfonate). The synthesized AAMS-1 was characterized with IR spectrum. Thermogravimetric analysis showed that AAMS-1 was chemically stable at 250℃. The synthesized AAMS-1 emulsion had particle sizes around 2,500 nm, with critical associating concentration of 0.15%. The network structure of AAMS-1 in fracturing fluids can be clearly seen using with an SEM. Fracturing fluids formulated with AAMS-1 have good viscoelasticity, sand carrying capacity, and permeability protection performance. Water solution of 0.6% AAMS-1 sheared at 150℃ and 170 s^-1 for 2 h had residue viscosity not less than 50 mPa·s, indicating that AAMS-1 had satisfactory shearing stability and high temperature stability.

A new hydrophobically associating polymer, LP-3A was synthesized through inverse emulsion polymerization, using AM, AMPS and monomers with hydrophobic chains and polyoxyalkylene groups as raw material, and benzoperoxide (BPO) as initiator. The polymerization conditions such as the optimum ratios of monomers, reaction time, temperature and initiator concentration etc. were determined through one-factor-at-a-time method. The molecular structure of LP-3A, a viscosifier used in fracturing fluids, was characterized, and the properties of LP-3A, such as temperature stability, shearing stability, recovery performance after shearing, viscoelasticity and thixotropy were studied. The study demonstrated that LP-3A had good high temperature stability and shearing performance. After being sheared under 150℃ and 170 s^-1 for 2 h, LP-3A still had residue viscosity of 200 mPa·s. After being sheared for 20 min at 500 s^-1 and 1,000 s^-1, respectively, shearing was stopped, and 90% of the viscosity of the LP-3A solution can be recovered. Compared with guar gum, energy needed to destroy the network structure of LP-3A was higher, and time needed for the recovery of the structure was longer. In the LP-3A fracturing fluids, elasticity prevails, and the viscoelasticity of LP-3A fracturing fluids is superior to guar gum fracturing fluids.