ABSTRACT: FT-IR Microspectrometry of Petroleum Inclusions : CH₄, n-alkanes, CO₂ and Water quantitative analysis

Pironon, Jacques¹, Régis Thiery², Frédéric Walgenwitz³, Mohamed Ayt Ougougdal⁴, Georges Baudoin⁴
(1) CNRS - UMR G2R, Vandoeuvre-lès-Nancy, France
(2) B. Pascal University, Clermont-Ferrand, France
(3) Elf Aquitaine, Pau, France
(4) Laval University, Québec, QC

Petroleum inclusions are ubiquitous in petroleum reservoirs and may be one phase (liquid or vapor), two phases (vapor bubble in a liquid phase), or three phases (vapor, liquid, and solid phases). Their composition and phase equilibrium are related to the PVTX conditions at the time of trapping. Bulk methods (i.e. GC-MS) can give quantitative composition of petroleum inclusions after crushing or heating. However, this composition does not take into account different oil generations, frequently trapped in diagenetic minerals.

We have developed a novel approach allowing individual petroleum inclusion analysis using FT-IR. Previous works have shown the ability of this technique to determine the CH2/CH3 ratio of the alkane fraction of the oil. Standard inclusions, rich in condensate gases, from Quebec area, gave us the opportunity to calibrate the CH4/alkane infrared ratio: a reference spectrum of CH4 is recorded in gas phase of a big inclusion. The composition of a two phases petroleum inclusion, homogenizing in critical phase, has been modeled. The ir spectrum of methane is subtracted from the spectrum of this critical inclusion and then, the CH4/alkane ratio is calculated. CO2/CH4 molar ratio is estimated from the relative ir absorption coefficients.

FT-IR microspectrometry can also detect the presence of water in petroleum inclusions. Coupled with a heating stage it determines the bulk homogenization (water in oil) temperature of petroleum inclusions.

Consequently, and for the first time, FT-IR individual analyses permit to model the oil composition of petroleum inclusions. These new data help us to reconsider PVTX interpretations of petroleum inclusion.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia