в документации по ДОА написано, что для работы с BLOB полями нужно использовать локаторы (лишнее выкинишь сам):

var
...
LOB: TLOBLocator;
...

begin
...
with DMForm.TempInOraQuery do begin
Clear;
SQL.Add('INSERT INTO '+AttachTableNameEdit.Text+' (Receive_Time, Dir_Name, Name_File, Body_File)');
SQL.Add('VALUES (:RecTime, :DirName, :Name_File, empty_blob())');
SQL.Add('RETURNING Body_File INTO :Body_File');
DeclareVariable('RecTime', otDate);
DeclareVariable('Name_File', otString);
DeclareVariable('Body_File', otBLOB);
DeclareVariable('DirName', otString);
SetVariable('DirName', TempDirInside);
SetVariable('RecTime', RecTime);
SetVariable('Name_File', searchRecFile.Name);
LOB := TLOBLocator.Create(DMForm.OraSession, otBLOB);
SetComplexVariable('Body_File', LOB);
Execute;
LOB.LoadFromFile(TempDir+'\'+SearchRecFile.Name);
LOB.Free;
end;
...
end;

вот что написано в документации:

You need to insert new LOB data into a table in two situations:

1. You are inserting a new record.
2. You are updating a record where the old value of the LOB column is null. In this case, the record does not contain a LOB Locator that you can use to write data to.

If you are not using a temporary LOB, you must first insert/update an empty LOB Locator into the record. To do so, you can use the SQL function empty_blob() or empty_clob() in an insert or update statement. On the server, the LOB Locator will be initialized. The initialized LOB Locator can then be returned to the client in a variable by using the new Oracle8 returning clause. After this, you can start writing data to the LOB column. Note that you must use SetComplexVariable to set a LOB variable.

The following is an example of an insert:

var LOB: TLOBLocator;

Buffer: array[0..99] of Byte;

begin

// insert into lobtable (id, lobcolumn) values (:id, empty_blob())

// returning lobcolumn into :lobcolumn

with LOBQuery do

begin

SetVariable('id', 1);

// Create a new BLOB (initially Null)

LOB := TLOBLocator.Create(Session, otBLOB);

// Assign it to the returning variable

SetComplexVariable('lobcolumn', LOB);

Execute;

// After the insert, use the LOB Locator to write the data

LOB.Write(Buffer, 100);

LOB.Free;

end;

end;

If you are using temporary LOB's, you can write the LOB data before executing the query, and directly use this LOB data for an insert or update without a returning clause:

var LOB: TLOBLocator;

Buffer: array[0..99] of Byte;

begin

// insert into lobtable (id, lobcolumn) values (:id, :lobcolumn)

with LOBQuery do

begin

SetVariable('id', 1);

// Create a new temporary BLOB and write the data

LOB := TLOBLocator.CreateTemporary(Session, otBLOB, True);

LOB.Write(Buffer, 100);

// Assign it to the returning variable

SetComplexVariable('lobcolumn', LOB);

// Insert it

Execute;

LOB.Free;

end;

end;