The Dolphins have invested heavily this offseason and need to fill their gaping hole at LT if they want to make the playoffs. Sitting at #12 their chances of someone falling to them are very low. Luke Joekel is likely to go #1 to KC, Eric Fisher won't fall out of the Top 5 and Lane Johnson has seen his stock rise as well.
Reports suggest the Dolphins like Joekel and Fisher immensely more than Johnson, so they decide it's worth it to trade up significantly. Philadelphia has already demonstrated interest in a tackle, so a trade with Oakland would be a logical choice. Fortunately, the Dolphins have the ammunition to pull this trade off. The Raiders pick up good value and more young talent for their rebuilding process.
Here is how the trade would shake out:
Miami receives pick #3 (2591 value points)
Oakland receives pick #12 (1716), #42 (626) and #82 (208)
Beyond the obvious benefit of getting more picks, the Raiders get back into the all-important second round which historically has the best "bang for the buck". Plus the players available at #12 vs #3 will help the rebuilding process more or less equally. I'm not saying the player will be as good, but with where the team stands at the moment this difference really doesn't impact the overall team quality much.