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.
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