Patent ID: 8020437

Claim:
A method to determine quality of a downhole fluid sample, comprising: locating a toolstring comprising a drill stem testing device downhole, the drill stem testing device having a chamber for collecting fluid samples; opening the chamber to induce flow of the fluid sample into the chamber and subsequently closing the chamber to trap the fluid sample; measuring at least one selected from the following list: a pressure inside a wellbore and a pressure inside the drill stem testing device; obtaining properties including at least one selected from the following list: initial pressure inside a formation, permeability of a formation, and skin factor; reconstructing a pressure history of the fluid sample by tracking the locations and pressures of the fluid sample from the formation into the chamber based on at least the obtained properties; and determining whether the pressure history of the fluid sample dropped below a critical pressure from the formation into the chamber; the critical pressure being a bubblepoint pressure for a liquid and a dewpoint pressure for a gas.