Technical Paper: Insitu Characterization of Formation Fluid Samples - Case Studies

Society: SPE
Paper Number: 90932
Presentation Date: 2004
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Sampling in the early stages of the exploration and development cycle is essential to provide key information for field planning and facilities design. In the majority of deepwater and other high cost wells drilled these days, formation tester samples may be the only source of fluid properties reliable enough to be used for economic screening. It is therefore critical to collect representative high quality samples early in any exploration or appraisal campaign. With the aid of real time insitu fluid characterization, sample quality can be assured, and the sampling process can be optimized. Insitu fluid characterization is essential for making decisions about where and when to sample, and how many samples to acquire. In that manner, maximum quality information may be acquired in an optimal amount of time. This is particularly critical in offshore deepwater sampling jobs, where rig rates can reach hundreds of thousands of dollars per day.

This paper describes how the latest techniques for downhole fluid characterization can be put to maximum use. These techniques include real time composition measurement, fluid type identification and single-phase assurance. The absorption properties of hydrocarbons in Near-Infrared spectroscopy and principal component analysis techniques are used to obtain real time composition. This includes carbon dioxide concentration, Gas-Oil-Ratio, and water volume fraction as well as the relative abundance of three broad reservoir fluid pseudo-components. Fluid type identification and single-phase assurance are achieved with downhole gas detection and fluorescence measurements. Fluorescence monitoring enables the detection of condensate formation if the dew point pressure of a wet or retrograde gas system is crossed during sampling. In some cases, it also provides a means of qualitatively distinguishing between gas, condensate, light oil, and heavy oil from oil-base-mud filtrate.

Several case studies are presented here to demonstrate the techniques of composition measurement, fluid type identification, and single-phase assurance. The case studies clearly show how these techniques help obtain high quality sample in an optimal amount of time.