Trace element content and distribution in a single fluid inclusion from Dunbar Oil Field, North Sea
Résumé
Synchrotron X-ray fluorescence (SXRF) analysis of individual fluid inclusions was performed on a suite of samples collected above and beneath a well-documented connectivity barrier of the Dunbar oil field, North Sea. The fluid inclusion analyzed consists of two phases (liquid + vapor), low salinity aqueous brines lining overgrowth zone of detrital quartz that formed during secondary silicification of the host sandstone. SXRF measurements indicate that the inclusion fluid contains a large variety of major and trace elements including CI, K, Ca, Ti, V, Cr, Mn, Fe. Co, Ni, Cu. Zn, Ga, Se, Br, Rb, Sr. Zr, Nb, Cd, Ba, Pb. Chemical mapping of a large inclusion (30 $\mu$m) together with element correlation diagrams show that, with the exception of Ca, Sr, Br and in lesser extent Zn, which display an homogeneous distribution throughout the inclusion, most elements show small-scale distribution heterogeneities that are best interpreted in terms of infra- $\mu$m solid phases suspended in the fluid phase. Calculated concentration estimates are critically dependent of the interpretation made for the origin of these solid phases (heterogeneous trapping vs. precipitated from the ambient inclusion fluid).