OracleConnection conn = new OracleConnection("...");
conn.Open();

OracleTransaction tx = conn.BeginTransaction();

OracleCommand cmd = conn.CreateCommand();
cmd.Transaction = tx;
cmd.CommandText = "update table set image=EMPTY_BLOB() where kod='01' RETURNING image INTO :tempblob";
cmd.Parameters.Add(new OracleParameter("tempblob", OracleType.Blob)).Direction = ParameterDirection.Output;
cmd.ExecuteNonQuery();
OracleLob tempLob = (OracleLob)cmd.Parameters[0].Value;
tempLob.BeginBatch(OracleLobOpenMode.ReadWrite);

/* здесь все действия по записи данных */
tempLob.Write(tempbuff,0,tempbuff.Length);

tempLob.EndBatch();
tx.Commit();