基于淀粉微球交联剂的低浓度羟丙基胍胶压裂液性能研究

Study on the performance of low-concentration hydroxypropyl guar gel fracturing fluid based on starch microsphere crosslinking agent

目的针对低渗透油藏,需要降低压裂液稠化剂用量,减少对储层的伤害,并确保压裂液具备延迟交联、携砂等性能和耐温耐剪切性能。方法利用反相乳液聚合法合成淀粉微球,通过硅配体和硼羟基修饰淀粉微球表面,制备了一种交联性能优良、伤害性低的微球型硅硼交联剂(KBSM)。结果KBSM交联剂能够实现多活性位点交联,增强交联密度,从而降低羟丙基胍胶(HPG)的用量,具有延迟交联特性。其延迟交联时间在2~6 min内可调。质量分数为0.2%的HPG交联冻胶在120℃、170 s-1剪切120 min后的黏度为80 mPa·s。交联冻胶中砂质量分数(以下简称携砂比)为40%时,陶粒沉降速度为0.1167 cm/min。加入质量分数为0.25%的过硫酸铵破胶剂可使交联冻胶在90℃下、120 min内完全破胶,且残渣质量浓度为214 mg/L。同时,破胶液的岩心损害率为26.55%。结论基于淀粉微球交联剂的低含量羟丙基胍胶压裂液对于降低低渗储层伤害有一定的指导意义。

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 0.1167 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.