We do this...sort of...except that its downstream of the compressors and the injection rate is about 1/4 of yours (25 bbl/mmcf). The injection points go into the middle of the pipe and are equipped with spray nozzles. One of the constraints on the control system also is keeping the injection rate per unit of volume a healthy safety margin away from the dew point at process conditions.
Personally, I have always found mixing to be a tough thing to predict well so I always go to an expert. In this case you also have to deal with evaporation which makes it even more complicated.
Things I would look closely at: time to get from injection point to compressor, distance from injection point to compressor, routing of pipe (ie elbows, etc.), temperatures (and how stable they are).
Another area to look closely at is control. Is 20,000 bbl/d an average number? Does this fluctuate a lot (short bursts of high flow)? If so, you will probably have problems.
Besides nozzles, you might have some luck with others things to atomize the liquids (or at least get some small drops or films) and get good quick mixing). Static mixers or some sort of other piping internals may help.