Oracle dump to csv and keep NULL as empty string
This is how I normally make .csv files.
You should be able to open the file with Excel.

SET TERMOUT OFF
SET FEEDBACK OFF
SET ECHO OFF
SET PAGESIZE 0
SET LINESIZE 2048
COLUMN text format A2048
SET VERIFY OFF
SET TRIMSPOOL ON
SET TAB OFF
SET UNDERLINE OFF
SET TERMOUT ON

SPOOL dump_audit_table.csv

SELECT '"'||timestamp||'","'||PROXY_SESSIONID||'","'||sessionid||'"' text
FROM dba_audit_trail where rownum &lt; 10;

SPOOL OFF
QUIT