(PHP 5, PECL OCI8 >= 1.1.0)
OCI-Lob::erase — Erases a specified portion of the internal LOB data
$offset
   [, int $length
  ]] )
   Erases a specified portion of the internal LOB data starting at a
   specified offset. If called without parameters, it
   erases all LOB data.
  
For BLOBs, erasing means that the existing LOB value is overwritten with zero-bytes. For CLOBs, the existing LOB value is overwritten with spaces.
offset
length
   Returns the actual number of characters/bytes erased  or FALSE on failure.