致密砂岩气藏提高返排效果技术对策

Countermeasures Against Improving Flowback Efficiency for Tight Sandstone Gas Reservoirs

压后排液是气井增产作业的重要环节,直接影响压裂改造的效果。岩心实验显示影响排液速度的主要因素为压裂液滤失后形成的启动压力以及返排压差,支撑剂回流受到地层闭合压力和破胶液黏度的影响。川西致密气藏由于水敏性强、水锁伤害严重,需要快速排液降低伤害,提出了水平井高效返排技术对策。一是采用液氮增能助排工艺为地层提供较大返排压差,并优化形成了"阶梯"降排量的伴注模式;二是采用纤维加砂工艺提高支撑剂在裂缝内的稳定性,在分段压裂每段施工末期进行一定比例的尾追。高效返排技术在中浅层应用超过30井次,提高了返排速度和最终返排率,保证了压裂改造的效果。

For most gas wells, flowing back after fracturing is a vital part of stimulation, which may affect directly a fracturing effect. Core experiments show that the main factors influencing flowback velocity are the start-up pressure caused by fracturing-fluid filtration and the flowback differential pressure; and the proppant backflow is influenced by formation closure pressure and the viscosity of gel breaking fluid. Due to strong water sensitivity and severe water-blocking damage existing in many tight sandstone gas reservoirs of western Sichuan Basin, a rapid drainage is needed to reduce this damage. Therefore, an efficient flowback technology of horizontal well is proposed. Firstly, liquid nitrogen energized-assisted drainage is adopted to provide a higher differential pressure of flowback, and a mode of accompanied injection with'stepped'discharge reduction is optimized; secondly, fiber sanding is used to improve the stability of proppant in fractures, and during a staged fractureing, a certain proportion of tail chase should be implemented in the final operation of every stage. This technology has been applied to over 30 wells in middle-shallow layers, resulting in improvement of flowback velocity and final flowback rate.