Now I'm in the process of planning DST in a Deepwater exploration well.
As you know, there is a high uncertainly in pore pressure prediction at exploration wells.
We plan to use brine as packer fluid and type of brine would be selected based on the best estimate of pore pressure of target formation. However, in case that the actual pore pressure has exceeded maximum available weight of prepared brine type, DST with under-balanced condition (under-balanced brine above DST packer) could be one of possible options.
I'd like to know information about DST operations with under-balanced condition.
Is this kind of operation performed commonly?
What types of risk do we need to assume for this operation?