Abstract
Refracturing is one of the most effective techniques to enhance the production of tight sandstone gas (TSG) well. Many TSG gas wells are facing the problem of water invasion after refracturing, the formation water may gradually occupy the gas-producing channels, preventing high gas productivity. In this paper, we newly developed a fuzzy-ball temporary plugging fluid (FTPF) with diverting fractures and water cutting after refracturing in one operation. The temporary plugging and water breakthrough control capabilities of the FTPF system were evaluated through the true triaxial large-scale core diversion fracturing experiment and matrix core and artificial fracture waterproof experiments. Meanwhile, the permeability damage evaluation experiments were performed to analyze the reservoir recovery ability. Results showed that the pressure-bearing capacity could reach up to 62.6 MPa, the rock fracture pressure was increased by 5–10 MPa compared with the initial hydraulic fracturing and an apparent fracture network structure was formed after refracturing. The breakthrough pressure gradients of simulated formation water were 2–10 times higher than that of nitrogen after the cores (including matrix and cores with 4 mm fractures) were plugged with FTPF, indicating its good water cutting ability. Before and after gel breaking, the permeability recovery value of the matrix core and the artificial fracture core was about 85–98%. The on-site application of FTPF to the refracturing of two TSG wells in the Sulige Gas Field in Northwest of China displayed that the average gas production has been enhanced by 64.8%. It is proposed that fuzzy balls can easily enter and gather at the tip of the initial fractures and form a stable pressure-bearing structure due to its viscoelastic properties and deformability. In addition, the hydrophilic fuzzy-ball core agents can adsorb on the rock's surface and form a polymer membrane, increasing the resistance of water flow.
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