Objective For low permeability oil reservoirs, reducing the amount of fracturing fluid thickener is important to minimize damage to the reservoir and to ensure that the fracturing fluid has delayed cross-linking, temperature and shear resistance, and proppant carrying capacity.

Methods This study aimed to develop a fracturing fluid system that minimizes damage to low-permeability reservoirs. Starch microspheres were synthesized using a reverse-phase emulsion polymerization method, followed by surface modification with silicon ligands and boron hydroxyl groups, to prepare a microsphere-type silicon-boron crosslinker (KBSM) with excellent crosslinking performance and low reservoir damage.

Results This study discovered that the KBSM crosslinker could enable multi-active site crosslinking, improve crosslinking density, and consequently reduce the concentration of hydroxypropyl guar (HPG) used on-site in oilfield fracturing. It exhibited delayed crosslinking characteristics with an adjustable 2-6 minutes. The viscosity of 0.2% HPG crosslinked gel was 80 mPa·s after 120 min at 120 ℃ and a shear rate of 170 s^-1. The crosslinked gel had a strong proppant-carrying capacity, with a proppant settling rate of 0.116 7 cm/min when the proppant concentration reached 40 wt%. The 0.25% ammonium persulfate breaker effectively broke the gel in low-concentration HPG fracturing operations carried out at 90 ℃, leaving a minimum residual mass concentration of 214 mg/L. Meanwhile, the average damage rate in matrix permeability caused by the broken gel was 26.55%.

Conclusion The low-concentration hydroxypropyl guar fracturing fluid based on starch microsphere crosslinking agents has a certain guiding significance for reducing damage to low permeability reservoirs.