压裂液屈服应力实验研究

Experimental Research on Yield Stress of Fracturing Fluid

压裂施工过程中裂缝内浓缩的压裂液具有较高的屈服应力,会导致压裂液返排效率低,有效缝长短。实验原理基于虎克定律,压裂液屈服前的应力与应变为线性关系;当其偏离线性关系时,压裂液屈服。采用自制实验装置考察了瓜尔胶与破胶剂浓度对压裂液屈服应力的影响。实验结果表明,瓜尔胶浓度较低时,压裂液屈服应力较小,瓜尔胶浓度4.8g/L时的屈服应力仅为0.329Pa;随着瓜尔胶浓度的增加,压裂液屈服应力迅速增大,瓜尔胶浓度为24g/L时,屈服应力增至63.292Pa。在压裂液中加入破胶剂可以有效减小压裂液的屈服应力。压裂液屈服应力为0时,瓜尔胶浓度与所需破胶剂量的关系近似为线性关系,瓜尔胶浓度越高所需破胶剂量越大。

During fracturing treatment,fracturing fluid concentrated in the fracture had significant yield stress which decreased the effective fracture length.The experiment theory was based on Hookes law.The relationship between stress and strain should be linear before fracturing fluid yield,which indicated that the fracturing fluid had yielded when the relationship departed linearity.The effect of the concentration of guar and breaker on the yield stress of fracturing fluid was measured by self-made experimental apparatus.The experimental results showed that the yield stress was of 0.329 Pa with 4.8 g/L guar.However,the yield stress increased quickly with the increasing of guar concentration.The yield stress of fracturing fluid had reached 63.292 Pa when the guar concentration was of 24 g/L.The yield stress could be decreased dramatically by putting breaker into fracturing fluid.When yield stress turned to zero,the relationship of the concentration between guar and breaker was near linear.