Single probe downhole sampling apparatus and method

摘要

A single probe system is utilized to quickly obtain uncontaminated formation fluid samples. The single probe includes an outer guard tube and an inner sampling tube which is slightly recessed relative to the outer tube such that the pressure at the front face of the probe is substantially uniform. Each tube is coupled to its own pump which controls the flow rate of the fluid moving through that tube. Knowing the size of the sampling tube relative to the size of the outer probe tube, and optionally based on relative viscosities of formation fluids and filtrates, the pumps are caused to generate a particular flow rate ratio through the tubes such that an appropriate pressure is maintained at the front face of the probe and such that the fluid flowing through the sampling tube is substantially uncontaminated.