Unfortunately the scenario is a bit different from a water well...

Unfortunately the scenario is a bit different from a water well drilled to a few hundred metres. You're dealing with very high formation pressures that you need to keep under control via a column of weighted drilling fluid in the borehole. You're also working at depths of 3-4000m.

To collect a sample of formation fluid in the above scenario requires isolating a small section or point on the borehole wall and getting the fluid to flow into a small sample chamber...without interfering with the ability of the mud column to keep the formation pressure under control. The sample chamber needs to be in connection with the formation via a probe that must penetrate any mud cake on the borehole wall and also not allow any mud in the borehole to leak past the probe packer and into the sampling flow line.