What is the ruling on repeatedly swearing not to practice oral sex with one's wife, and does it require expiation? What are the consequences of practicing it in the future after these oaths?

As for the enjoyment in this manner between spouses, it has been previously detailed in fatwas number: 31122 and 39916.

Regarding the oaths you swore, for every oath you broke by returning to the act with your wife, you owe an expiation for breaking an oath. If you swore not to do it in the future and you did not do it, then there is nothing upon you. But if you do it in the future, then you must expiate for your oath, and the permissibility or impermissibility of the act remains subject to the guidelines mentioned in the previous fatwas.

The expiation for breaking an oath is feeding ten needy persons, or clothing them, or freeing a slave. If one cannot find any of these, then it is fasting for three days, as in His (Allah's) saying: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [or afford it] - then a fast of three days. That is the expiation for your oaths when you have sworn" (Al-Ma'idah: 89). Refer to the detailed explanation in fatwa (definition) number: 31077.