套管孔眼压裂冲蚀大型现场实验研究

Large-Scale Field Experimental Study of Casing Perforation Erosion During Fracturing

限流压裂过程中,携砂液高速流经射孔孔眼会产生严重的冲蚀现象,孔眼形态发生改变,导致孔眼限流作用失效,直接影响压裂改造效果。为明确限流压裂条件下孔眼冲蚀规律,本研究设计并搭建了孔眼冲蚀大型现场实验模拟系统,孔眼流速可达到191 m/s,套管压力达到35 MPa以上,采用真实压裂材料进行模拟实验,针对压裂施工的主要参数对套管内壁孔眼冲蚀规律进行实验研究。实验结果表明:井筒内壁孔眼冲蚀分布存在明显的不均匀性,孔眼优先沿跟端侧发生形变;压裂液黏度增大有助于孔眼限流作用保持;相同工况条件下,陶粒组冲蚀速率大于石英砂组;冲蚀速率对排量较为敏感,排量增大会加速孔眼限流失效;冲蚀速率与砂比间呈非线性关系,孔眼冲蚀速率在砂比7%~16%范围内相对稳定,砂比超过16%后,孔眼冲蚀速率急剧增大,在施工过程中建议将砂比控制在16%以下,可减缓孔眼冲蚀导致的孔眼形变。

In the process of limited entry fracturing,sand-carrying fluid flowing through perforation at high speed will cause serious erosion and change the perforation morphology,resulting in the failure of limited entry effect,which directly affects the fracturing effect.In order to clarify the law of perforation erosion under limited entry fracturing conditions,in this study,a large-scale field experimental simulation system for perforation erosion was designed and established,where the perforation flow velocity can reach 191 m/s and the casing pressure can exceed 35 MPa,real fracturing materials were used to simulate experiments,and the erosion law of casing inner wall perforation was studied according to the main parameters of fracturing operation.The experimental results show that:the distribution of perforation erosion in the inner wall of the wellbore is obvious uneven,and the perforation is preferentially deformed along the heel side;the increase of fracturing fluid viscosity helps to maintain the flow restriction of perforation;the erosion rate of ceramic granule group is larger than that of quartz sand group under the same working conditions;the erosion rate is sensitive to the discharge volume,and the increase of discharge volume will accelerate the failure of perforation flow restriction;the relationship between erosion rate and sand ratio is non-linear,and the erosion rate of perforation is relatively higher in the range of 7%-16%of sand ratio.The erosion rate of perforation is relatively stable within the range of 7%~16%of sand ratio,but after the sand ratio exceeds 16%,the erosion rate of borehole increases sharply,so it is recommended to control the sand ratio below 16%during the operation,which can slow down the deformation of perforation caused by erosion.