The reason oil prices have come down is because OPEC has cut prices arbitrarily. They were artificially high to begin with. On average it costs an OPEC nation ~$30 to produce a barrel of crude. They're still making a shitload of profit.
It's not arbitrary at all, and it's not really OPEC, as many OPEC members would rather see higher prices for their own internal political reasons. The primary driver is Saudi Arabia, who is trying to crush the shale oil producers in the US (particularly, and to some extent Canada) where oil cannot be produced at profit for less than $80 a barrel. A sustained price below that point is
intended to chase US firms out of the market, as they can't produce profits at this level, which in the long-run would be good for Saudi Arabia.
Prices aren't "set" in that way. It is primarily a global auction market price, with some lesser side-deals.
What the OPEC countries do is set and publish production targets for themselves. Sometimes they also violate these targets and release more oil than they say that they will behind the backs of the cartel partners.
To say what is "intended" by them is essentially a bizarre claim of mind-reading. There may well be other intentions entirely, (such as maintaining the largess of their regime and thus forestalling a democratic revolt) and the effects on USA and Russia may be merely side effects and unintended consequences, or even simply not as big of a factor as other financial concerns of selling enough oil as they feel that they need to sell.
Not all effects of actions are controlled. Even children know this the first time they accidentally break something.