Bottom Hole Sampling Method

In order to provide a good sample for PVT analysis, bottom hole sampling method is one of the best way. Bottom hole sampling usually not suitable for gas-condensate reservoir and oil reservoir with substantial quantity of water. The production bottom hole sampling operation involves running a special sampling tool into the well on wire line, so that a sample of the fluid in the well can be collected under the increased pressure of the fluid column. It is also needed some of the high technology apparatus on the surface in order for getting a much better sample properly.

Bottom hole sampling represents the simplest and most convenient mechanism for collecting representative reservoir fluid samples. Basically, the bottom hole sample can represent fluid at their true reservoir, but the challenge is to avoid the contamination from occurred in the fluid sample. Sample that already contaminated with impurities can affecting the result from PVT analysis, which making characterization process of the particular reservoir became more difficult. The other thing is, bottom hole sampling is a very expensive and

Drilling mud especially Oil Based Mud (OBM) will infiltrate the fluid collected by the probe, resulting in significant mud filtrate contamination. This happens even after pumping out for hours before collecting a sample at that situation. In comparison with Water Based Mud (WBM), such contamination can be easily separated in the laboratory while for OBM, contamination is more difficult to detect and literally impossible to remove it from the sample. Drawdown pressure must be controlled to ensure a true reservoir fluid sample is attained. If the drawdown pressure is too large, the fluid can end up spill out into multiple phase at the wellbore, resulting the highly difficult problem occurred because sampling vessel might not retain both phase