海水基速溶低摩阻胍胶压裂液的研究

海上油田压裂采用海水配制压裂液成为降本增效的有效技术手段，但海水水质具有硬度高、矿化度高等问题。针对此问题，笔者将胍胶原粉分子重建物理改性，并经羟丙基化学改性，取代度0.45的两次改性胍胶在海水环境中3 min增黏速率达90%，相比普通同取代度的羟丙基胍胶，分子重建羟丙基胍胶在海水中增黏速度明显提升。交联剂通过对比，优选树状大分子有机硼交联剂，由于硼原子在交联过程中扩散速率降低，在应用阻垢剂基础上交联胍胶过程中可实现延迟交联，形成的冻胶微观网格尺寸平均40～55 nm，比小分子络合硼交联冻胶网格尺寸大，有效延迟交联速度，降低压裂摩阻。由分子重建羟丙基胍胶、树状大分子有机硼交联剂制备的海水基压裂液经在120℃剪切，2 h的流变性能为200 mPa·s，大于行业标准，降阻率可达80%，黏弹性能高于一般小分子络合硼交联胍胶。 

Study on Instant Low Friction Seawater Based Guar Gum Fracturing Fluids

To reduce operation cost, sea water is frequently used to formulate fracturing fluids for fracturing offshore wells. Sea water generally has higher hardness and higher salinity, which are adverse to the viscosity development of fracturing fluids. To solve this problem, a guar gum was first physically modified by molecule reconstruction followed by chemical modification with hydroxypropylation. This physically and chemically modified guar gum of a degree of substitution (D.S.) of 0.45 can efficiently viscosify sea water, with rate of viscosification reaching at 90% in 3 min. Compared with conventional hydroxypropyl guar gum of the same D.S., the molecule-reconstructed hydroxypropyl guar gum viscosifies seawater in an obviously fast manner. By testing the performance of different crosslinking agents, the dendrimer organoboron crosslinking agent was selected because the diffusion rate of boron atoms in the course of crosslinking is low, by using scale inhibitor, the crosslinking process can be delayed, and a gel whose average microgrid size of 40-50 nm was formed. The grid size is greater than the grid size of a gel formed by low molecular weight complex agent instead of dendrimers, and this helps delay the crosslinking rate of guar gum effectively and thus reduces the friction and drag of the fracturing fluid. Laboratory evaluation of the seawater fracturing fluid formulated with molecule-reconstructed hydroxypropyl guar gum and dendrimer organoboron crosslinking agent showed that after aging at 120℃ for 2 hours, the viscosity of the fracturing fluid was 200 mPa.s, greater than the value specified in the industrial standard and the flow resistance was reduced by 80%. The viscoelasticity of this fracturing fluid is greater than the boron-complexed guar gum using low molecular weight complex agents.