一种可回收清洁压裂液的研制和应用

在长庆油田体积压裂施工中需要配制大量压裂液，为避免大量消耗水资源，需对压裂液进行回收利用，而长庆区域普遍使用的羟丙基瓜胶体系回收后不能用于携砂，低分子瓜胶压裂液的回收利用工艺复杂。因此研制了一种可回收的清洁压裂液，该压裂液由3% XYCQ-1稠化剂、0.05% XYPJ-2破胶剂及（0.01%~0.10%）XYTJ-1水质调节剂构成。XYCQ-1稠化剂是将蔗糖经微生物培育、发酵而得到的一种微生物多糖稠化剂，在10 s内可使压裂液黏度趋于稳定，增稠快。XYPJ-2破胶剂是一种天然酶和分子改造酶的混合物，由特异水解稠化剂的多糖构成，通过对稠化剂分子结构进行定点突变，促进酶有针对性的反应，形成非天然的新二硫键，从而保证了破胶液的再次成胶反复使用。XYTJ-1水质调节剂与返排液中的Ca2+、Mg2+等高价金属离子可形成溶于水的络合物或螯合物，消除高价离子对成胶的不利影响。实验表明，该压裂液耐温80.0℃，且有较好的悬砂、降阻及助排性能，在常温静置24 h和80℃水浴中静置15 min后基本无沉降，注入排量为64 L/min时降阻率为67%，岩心损害率仅为6.70%。该压裂液在长庆区域油水平井体积改造中应用21口井，施工用液10.46×104 m3，返排液经分离沉砂等简单处理后即可再配压裂液，处理工艺简单，且回收液配制的清洁压裂液携砂性能良好，现场回收利用多达10次，表明该新型清洁可回收压裂液能满足多级压裂施工要求。 

The Development and Application of a Recyclable Clear Fracturing Fluid

Stimulated reservoir volume fracturing operation in Changqing oilfeld requires large amount of fracturing fluids. To save water, fracturing fluids are required to be recycled. However, the recycled hydroxypropyl fracturing fluid presently commonly used in Changqingdoes not have the ability to carry sands, and the technique for recycling low molecular weight guar gum fracturing fluid is not feasible for feld use. A recyclable clear fracturing fluid was developed recently in an effort to solve these problems. This fracturing fluid was formulated with 3% XYCQ-1 (a thickening agent), 0.05% XYPJ-2 (gel breaker), and 0.01%-0.1% XYTJ-1 (a water quality conditioner). XYCQ-1 is a polysaccharide thickening agent made by microbial cultivation and fermentation, and has the ability to render fracturing fluid stable viscosity in only 10 sec. XYPJ-2 is a mixture of a natural enzyme and a molecularly modifed enzyme, composed of the same polysaccharide as that in XYCQ-1. Site-specifc mutagenesis was used on the molecular structure of the thickening agent to promote specifc reaction to the enzymes to form non-natural new disulfde bond, thereby ensuring the gel resuming and recycling of gel-broken fracturing fluid. XYTJ-1, by reaction with Ca2+ and Mg2+in the recycled fracturing fluid to form watersoluble complexes or chelates, eliminates the negative effects of high valence metal ions on gel formation. Laboratory experiments indicated that the properties of the fracturing fluid remained stable at 80℃, and had good sand carrying capacity, frictionreduction and cleanup capacity. Almost no sedimentation was found of the fracturing fluid kept quiescence at room temperature for 24 hours, or stayed in 80℃ water bath for 15 minutes. At injection rate of 64 L/min, the percentage of friction reduction was 67%, and percentage of core damage only 6.70%. In the stimulated reservoir volume fracturing operation in 21 horizontal wells in the Changqing oilfeld, 10.46×104 m3 fracturing fluid was consumed, and the recycled fracturing fluid, after simple treatment (liquid-sand separation by settling), was reused for making fracturing fluid. The fracturing fluid has been recycled for 10 times, and the clear fracturing fluid made from the recycled fracturing fluid has good sand carrying capacity, indicating that the recyclable clear fracturing fluid has satisfed the needs of multi-stage fracturing operation.