CREATE OR REPLACE DIRECTORY documents AS 'C:\';

SET SERVEROUTPUT ON
DECLARE
  l_file    UTL_FILE.FILE_TYPE;
  l_clob    CLOB;
  l_buffer  VARCHAR2(32767);
  l_amount  BINARY_INTEGER := 32767;
  l_pos     INTEGER := 1;
BEGIN

    SELECT some_data
      INTO   l_clob
      FROM   some_table
      
  l_file := UTL_FILE.fopen('DOCUMENTS', 'report.txt', 'w', 32767);

  LOOP
    DBMS_LOB.read (l_clob, l_amount, l_pos, l_buffer);
    UTL_FILE.put(l_file, l_buffer);
    l_pos := l_pos + l_amount;
  END LOOP;
  
END;

l_clobLen := DBMS_LOB.GETLENGTH(l_clob);
  
 WHILE l_pos < l_clobLen LOOP
    DBMS_LOB.read (l_clob, l_amount, l_pos, l_buffer);
    UTL_FILE.put(l_file, l_buffer);
    l_pos := l_pos + l_amount;
  END LOOP;