Objective  The purpose of implementing high-pressure filling sand control or fracturing sand control in the 139 block heavy oil reservoir is to improve the oil flow channel. Due to the high viscosity of the heavy oil, a viscosity-reducing agent is used to reduce its viscosity and improve its fluidity. However, the process is complex and costly. To reduce the application cost, a new type of sand-carrying fluid with a viscosity-reducing effect on heavy oil was developed.

Method A hydrophobic associative polymer was developed by aqueous solution polymerization using acrylamide, acrylic acid, Gemini cationic surfactant, and 2-acrylamidoalkyl sulfonic acid as monomers. The polymer structure was characterized by infrared spectroscopy. Combined with viscoelastic surfactant and pH regulator, a sand-carrying fluid with heavy oil viscosity-reducing effect was developed. Its viscosity, shear resistance, sand-carrying capacity, gel breaking performance, and viscosity reduction efficiency were evaluated in the laboratory.

Results The existence of hydrophobic monomer structural units in the polymer was verified by infrared spectroscopy. The initial viscosity of the sand-carrying fluid was 240 mPa·s. At the temperature of 90 ℃ and the shear rate of 170 s⁻¹, the viscosity of the sand-carrying fluid after shearing for 120 minutes was 75 mPa·s. After the sand-carrying fluid was maintained at a constant temperature of 90 ℃ for 60 minutes, the settling rate of 0.425~0.850 mm quartz sand was 0.77 mm/s, indicating that the sand-carrying fluid has good sand-carrying performance. After adding ammonium persulfate and completely breaking the gel at 90 ℃, the viscosity of the gel-breaking fluid was 2.37 mPa·s, the surface tension was 26.34 mN/m, and the interfacial tension was 1.36 mN/m, achieving a viscosity reduction rate of over 98% for the heavy oil in Zhuangxi. The sand-carrying fluid was used in 12 wells in this reservoir. The average consumption of the sand-carrying fluid for a single well was 179 m³, and a sand addition was 23.2 m³ for a single well. Due to the effects of the sand-carrying fluid, the average oil production rate per well increased by 4.3 t/d.

Conclusion In heavy oil reservoirs, the use of this sand-carrying fluid for high-pressure sand control can significantly increase heavy oil production without the need for viscosity reduction construction. This study provides an efficient technical solution for sand control in heavy oil reservoirs.