1) There aren't too many "specifications" for water re-entry for fracking. The problem is that if the water is not 'cleaned' well enough, the turbidity (cloudiness and toxic mix) will clog downhole or simply not effectuate the intended flow of hydrocarbons back up the pipe. So, the goal of cleaning Process and Flowback water for re-use as frac water is to have the turbidity reduced to less than 15,000 (15 thousand or 15k) Parts per Million... preferably 5k/PPM. Thence, lubricants, descalers, etc. are added to the water and used for fracking.
2) Treated water, if cleaned well enough, can be used for agriculture or simply injected back into the aquifer a mile down the pipe and let nature finish the filtering over time. In general, most companies find a way to deal with excess water- whether by having a treatment company take over the responsibility, or in good cases- to use for agriculture and/or simply cast into a holding pond or ground cover and let it seep into the ground. We filter water down to appx 100 PPM, extremely clean (pure), and agriculture is an excellent option. We usually try and replace ponds and small lakes with the cleaner water we produce. Technology is rather great these days.
3) Treated water (cleaned) can be used for pretty much any other after-purpose, so long as it is tested to be purified. Note that I say this in terms of legitimate and conscientious purpose- not to evade EPA or Corps of Engineers regulations by doing only the minimimum. Our water, after filtering, is so clean that it is cleaner than the minimum EPA and CoE city requirements by more than 900%, so it comes down to sale. Farms and ranches do not mind at all, if you can prove your water is cleaner than their own wells. Cities and municipalities... well, it becomes a mental thing of whether or not the locals want to drink water they know came from fracking. Regardless of the quality, some thoughts and doubts will always stay in the back of one's mind.
4) The recovered oil from filtering is guided into tank batteries and sold, just as with other oil. It's up to the frac water co and the well developer to decide who gets to be responsible/benefit from such lefftovers. Generally, we, as the water filter group, are only handed the sludge and dirty water from Flowback and Process, and removing the water away from the well head is more important than arguing over residual oil. Generally, since we can clean Process and Flowback water at upwards of thousands of barrels (bb) per day, the principles/drillers are happier knowing that they have an on-site source of immediate frac water, saving days and multiple tanker charges- than worrying about profiting from residue harvesting. They have bigger things to worry about. Excess oil is rarely simply disposed of as pure waste- this is because most frac water filter companies are engineered to capture excess oil residue for profit, as an elementary part of any basic system. Money is money.
5) If you send me your e-mail address, I will send you a sample of engineering tests done on Flowback and Process water .
Good luck in your search!