Online Journal for E&P Geoscientists

Jourdan, Anne-Lise ^*1; John, Cedric M.¹; Davis, Simon ¹
(1) Earth Science and Engineering, Imperial College London, London, United Kingdom.

The “clumped isotope carbonate paleothermomether” can determine within a few degrees the temperature of formation of a carbonate mineral without having to know the composition of the fluid from which it precipitates. The novel field of clumped isotopes geochemistry relies on the natural abundance of CO2 molecules containing two heavy isotopes (i.e. 13C18O16O with a mass of 47), which are temperature-dependant because more ordered systems are more stable at low temperatures. Temperatures are thus determined by measuring the differences between a theoretical stochastic distribution of the isotopes among the molecules and their actual distribution in the lattice of the carbonate crystal.

In this study, we aim to improve the characterization of subsurface reservoirs in Qatar for CCS and EOR operations. Modifications of the reservoirs by diagenesis, either related to fault zones or to the rock matrix, are a major component in possible changes of the petrophysical properties of carbonate reservoirs. Therefore, understanding the diagenetic history of a reservoir is essential. Consequently, we are calibrating clumped isotopes thermometry for diagenetic cements. The current clumped isotopes calibrations are limited to lower temperatures and ambient pressure, and do not necessarily reflect reservoir conditions.

Our contribution will highlight the details and challenges of the calibration and manual preparation of clumped isotopes measurements. One of our aims is to reduce the size of the sample needed (presently 5mg) in order to be able to measure individual generations of cement, and understand every stage of the diagenetic process. Two different protocols for sample preparation have been tested and are being compared. Different methods have been used for mass spectrometer measurements to improve the quality of the measurements.

We will also show the preliminary results of temperature and pressure-controlled mineral precipitation experiments to be used for the calibration. Different carbonate minerals are being synthetically precipitated in the lab, from different compositions of solutions and at different temperatures and reservoir pressures.

The project is part of the Qatar Carbonate and Carbon Storage Research Centre (QCCSRC), funded jointly by Qatar Petroleum, Shell and the Qatar Science and Technology Park.