天然裂缝对水力压裂的影响研究

Influence of Natural Fractures on Hydraulic Fracturing

从裂缝的微观延伸出发,从理论上剖析了井壁附近天然微裂缝在裂缝连接、裂缝延伸方面的作用:在水力裂缝延伸沿程的天然裂缝会改变水力裂缝的传播方向,从而使裂缝的连接性能变差,产生多条水力裂缝;在射孔边缘的天然裂缝,虽然在方位上对裂缝连接极为不利,但仍可能成为水力压裂裂缝的最初通道,直接改变裂缝的延伸方向,使得裂缝自然连接的过程变缓或失败。应对措施,一是加入细陶或微陶,封堵部分狭窄裂缝,兼降滤作用;二是在前置液中加入柴油,降低滤失;三是缩小射孔段的长度,减少裂缝的起裂点。

During the operation of hydraulic fracturing in the reservoirs with the growth of carboniferous natural fractures, abnormal high pressure and sand fallout were commonly induced, sometimes operation failure resulted in, the basic cause was multi-fractures. Studying from a microscopic extension of fractures, the action of natural fractures on its connection and extension induced near the wellbore was analyzed theoretically: the natural fracture along its extension path would change the fractural transmission direction, result in poor fracture connection and induce multiple hydraulic fractures. Although the natural fractures on the margin of perforation were unbeneficial for its connection in azimuth, it was possibly the most initial channel of hydraulic fractures, by which the direct change of extension orientation and slow down or failure of its natural connection were caused. In allusion to the above situations, countermeasures taken include that ①fine and micro ceramic shots are deployed to block part of the narrow fractures and reduce the filtration; ②diesel oil is added into pad for filtration reduction; ③perforation length is shortened to decrease the crack point of fractures.