There is no OJEE as the admission will be based on Jee main score/rank only but in case there are vacant seats left then the special OJEE will be held after end of OJEE 2018 counselling for JEE Main 2018 candidates so you are advised to prepare for Jee main properly and get required rank so that you can easily get seat in Orissa colleges so there would be no requirement to be dependent on its special entrance exam.

Also, to check how to prepare for Jee main 2018, you can go through the below link -

https://engineering.careers360.com/articles/how-prepare-for-jee-main

Good Luck!!!