Recombined surface samples are usually used for volatile oil laboratory fluid property studies. A procedure for stabilizing and surface sampling of volatile oil wells is currently used in the industry. However, no investigation of the quality of the samples resulting from this procedure has ever been published.

Typically, during surface sampling, bottom-hole flowing pressure is less than the bubblepoint pressure of the original reservoir oil. This causes gas to form in a cylinder of the reservoir around the wellbore. Understanding the dynamics of this cylinder of gas saturation is critical to obtaining a recombined surface sample representative of original reservoir oil. It is possible to obtain a representative sample if this cylinder is stable.

This paper presents the results of a study of the sampling procedure. The effects of production rate prior to and during the sampling process were quantified using radial compositional simulation. The buildup and stability of the ring of gas saturation were examined.

Guidelines for sampling volatile oil wells is presented. It is based on comparisons of the compositions of recombined surface samples with the compositions of original reservoir oils for various producing schemes. These guideline are expected to give the best chance of obtaining a representative sample from a volatile oil well.

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