Importance

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Abstract

A method and apparatus for downhole formation testing is provided for acquisition of a phase intact sample of connate fluid by direct or indirect pumping for filling of pressure containing sample tanks that are removable from a formation testing and sampling instrument for phase intact transportation to a laboratory facility. One or more fluid sample tanks contained within the instrument are filled with connate fluid samples in such manner that during filling of the sample tanks the pressure of the connate fluid is maintained within the predetermined range above the bubble point of the fluid sample. The sample tank incorporates an internal free-floating piston which separates the sample tank into sample containing and pressure evacuation chambers. During indirect pumping a positive displacement piston pump draws fluid from the pressure evacuation chamber and permits formation pressure to shift the separator piston as the first variable volume chamber is filled with a connate fluid sample. The sample tank is provided with a cut-off valve enabling the pressure of the fluid sample to be maintained after the formation testing instrument has been retrieved from the well bore for transportation to a laboratory facility. To compensate for pressure decrease upon cooling of the sample tank and its contents, the piston pump mechanism of the instrument has the capability during direct pumping for increasing the pressure of the sample sufficiently above the bubble point of the sample that any pressure reduction that occurs upon cooling will not decrease the pressure of the fluid sample below its bubble point.

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