Abstract

Texaco's Exploration and Production Technology Department has developed two fluorescence techniques to enhance the detection of crude oil extracted from formation samples and to improve mudlogging as a formation evaluation tool.

The first of these is a portable field method called the Quantitative Fluorescence Technique (QFT™), which uses a single excitation wavelength and a short range of emission wavelengths. The intensity measurements are used to generate an oil concentration profile of the well. This method has proven successful in locating oil-bearing zones that were difficult to identify using conventional mudlogging techniques.

The second technique uses a more sophisticated ultraviolet (UV) spectroscopic instrument and is called the Total Scanning Fluorescence Technique (TSF™). This method generates a three-dimensional fluorescence spectra or fingerprint. The spectra results from the total fluorescence contribution from each of the fluorescing species in the oil. The unique chemical makeup of different crude oils gives spectral characteristics that can be used to predict oil composition or type. This method gives more information than conventional fluorescence techniques.

This paper discusses the effectiveness of these fluorescence methods in identifying crude oil, even in the presence of similar fluorescing substances commonly added to drilling muds, such as base oils or diesel. It also includes a feasibility study that demonstrates the application of these methods in a North Sea well drilled with an oil-based mud. Other examples are cited to show how these methods worked in offshore wells in the Mediterranean, and an offshore well in the Gulf of Mexico.