Exploration Applications of Downhole Measurement of Crude Oil Composition and Fluorescence

Abstract

TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractIn addition to geological and petrophysical data acquisition during the exploration stage, in-situ fluid analysis provides a wealth of information for the appraisal of new discoveries. A recently introduced wireline sampling tool incorporating a downhole fluid analyzer is capable of analyzing fluid composition in real time at downhole conditions, and of measuring the fluorescence spectra of crude oils. These new measurements provide valuable information necessary for the identification and validation of reservoir structures that define the distribution of fluids in the accumulation. The relevance of high quality fluid data in the early stages of the producing life of the reservoir is widely recognized. We present field results of the application of the new sampling tool in an exploration well, where a composition gradient was detected along a 30m liquid hydrocarbon column grading from a 45API crude on the top to a 33API crude on the bottom. During the sampling of the gas cap, retrograde dew formation was detected identifying the fluid and identifying valid sampling conditions. This new information was used to modify the sampling program. Fluid composition analysis relies on optical absorption methods and is currently capable of providing the mass fraction of three hydrocarbon molecular groups: C1, C2-5 and C6+, and CO2.We perform fluorescence spectroscopy by measuring light emission in the green and red ranges of the spectrum after excitation with blue light. Fluorescence in this range is related to the concentration of polycyclic aromatic hydrocarbons (PAH's) in the crude oil. Using the pump-out module to segregate different fluid phase enhances phase detection with fluorescence.

A regression model for estimation of dew point pressure from down-hole fluid analyzer data

“…The development of these tools was to address several production problems (e.g., sizing of facilities, well placement, completions equipment, and production prediction). According to Betancourt et al (2004Betancourt et al ( , 2007, the Composition Fluid Analyzer (CFA) is a tool which has a sensor for performing fluorescence spectroscopy by measuring light emission in the green and red ranges of the spectrum after excitation with blue light. It was originally introduced in order to track phase transitions in gas condensate sampling.…”

The Impact of Reservoir Fluid Compositional Variation and Valid Sample Acquisition on Flow Assurance Evaluation

“…[11] Detection of multiple (hydrocarbon) phases is greatly augmented by the phase separation that takes place in the pumpout unit. The fluids have a finite residence time in the pumpout enabling gravity segregation to give pure phases.…”

Reservoir Architecture Characterization From Integration of Fluid Property Distributions With Other Logs

“…However, fluorescence is very sensitive and can detect small amount of liquid dropout in real time even when the pressure is slightly below the dew point, thereby ensuring high-quality representative condensate gas samples. Figure 2 shows an example in which liquid dropped out of a condensate gas due to the pressure below the dew point, and the fluorescence signal gave the clearest evidence compared to fluid composition and water fraction (Betancourt et al, 2004;Dong et al, 2005). In addition to single phase assurance, fluorescence properties also aid fluid type identification when different fluids share the same absorption spectroscopy signature.…”