Drill Stem Testing has been described as 'Old School' technology for evaluating oil and gas wells. There are exceptions to this misconception. One is the system used by Horizontal Well Testing of Calgary, Alberta. This is a unique, totally electronic DST system that uses wireline inside the drill pipe and a wet connect to power up the downhole tools and receive telemetry for: formation, hydrostatic, temperature, inflate and recovery fluid pressures (over 15 years and 1500 DST's so far).
This DST system can be run in vertical, deviated and horizontal wells. It has the capability of not only showing the hydrostatic head pressure of recovered fluids inside the drill pipe but you can now use their Recovery Logging Tool (RCT) to run into the drill pipe after the final shut-in and measure the density of the various fluids that may have entered the drill pipe during the testing of the formation. You can then look at the Recovery Log and with confidence say this is drilling mud, this is water or this is oil.
This has been an old question and at present Horizontal Well Testing is the only Drill Stem Test Company in the world that can offer this new service to their customers. Pulling the test string and using a mud can to drain each stand and identify the recovered fluid and grab a sample is not a safe option. Also, if you want to run multiple tests on one run in the well it will be very difficult if not impossible to determine what fluid came from which formation. Now you can log the recovery after each zone has been tested and say with confidence what each one produced and how much!
You can run a wireline sampler in conjunction with the Recovery Logging Tool and obtain a conclusive sample from the recovery fluid of each zone. Trying to catch samples while reversing the recovery fluids out of the drill string is difficult and the samples usually are not representative of what flowed in during the flow periods. More often than not you end up with a blended recovery mixed with lots of drilling mud.