Thank you very much for your question. It is our pleasure to answer it.

In the name of Allah, We praise Him, seek His help and ask for His forgiveness. Whoever Allah guides none can misguide, and whoever He allows to fall astray, none can guide them aright.

The intention to perform a specific prayer is obligatory (fard). It is one of the pillars of prayer. Any act of worship without a valid intention will be invalid. It has been narrated that the prophet (peace be upon him) said, "(The value of) an action depends on the intention behind it. A man will be rewarded only for what he intended. The emigration of one who emigrates for the sake of Allah and His Messenger (peace be upon him) Allah and His Messenger (peace be upon him) on of one who emigrates for gaining a worldly advantage". (Muslim) 

Before offering prayer bring to mind the following points: 

1- Which prayer of the day you are praying. Is it Zhuhr or `Asr, etc?

2- Are you praying behind an imam in a congregational prayer or individually? 

It is not obligatory to utter the intention. Verbal intention is an innovation. There is no authentic hadith from the Prophet (peace be upon him) or any one of the companions or the salaf that one has to utter the intention before offering prayer. The sunnah and correct way to make intention is in your heart.

I hope this answers your question.