Case insensitive search of CLOBs in Oracle 12
Searching without any kind of index seems to be not a good idea. And an analysis without further details is difficult. But you can add resources to improve your speed.
It seems that the bottleneck of your query is CPU and not the disks. If disk speed is the limitation there would not be a difference between regexp and LIKE.


You can try to parallelize your query. If the work is done by 4 processes instead of one, it is possible that the query response tim is a quarter of the original time.
you can add an additional clob field that contains the content of dataClobfield  in uppercase. this field is used for searching the records you are interested in