The aperture through which the sand runs is so tiny that first it seems as if the level in the upper glass never changes.
沙子穿过的孔太小了，第一次看到它时就好像上面的沙子永远没有变化。
Reasonable aperture of sand prevention meshwork is important if liner in sand prevention of horizontal well is adopted.
水平井若采用筛管防砂，合理的防砂网孔径的确定尤为重要。
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