24 PLUGGED BASE PIPE FOR SAND CONTROL The flow apparatus of a perforated mandrel are temporarily sealed by plugs which are made of a sacrificial material, for example, zinc, aluminum and magnesium. The plugs prevent dirty completion fluid from passing through the screen as it is run into the hole, thereby protecting the screen from plugging. While the screen mandrel is temporarily sealed by the plugs, cleaning fluid is circulated through a work string and is returned through the annulus between the screen and the well bore for removing filter cake, drilling debris and lost circulation material. After the annulus has been cleaned, it is filled with an acid or caustic solution, which dissolves the sacrificial plugs. In an alternative embodiment, each sealing plug has a vent pocket sealed by a stub portion which projects into the mandrel bore. The screen mandrel flow apertures are opened by mechanically shearing the stub portion of each sealing plug.
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