Diagenetic research on samples from the Beerse geothermal well GT 01 A

Abstract

This report focusses on the reconstruction of the diagenetic history and reservoir properties of the dominantly Dinantian carbonate succession in the Beerse area, based on cuttings of the geothermal Beerse GT 01 A borehole. After a binocular inspection of representative cuttings displaying diagenetic features, thin sections were prepared for classical petrographic, cathodoluminescence (CL) and fluorescence microscopy inspection. Geochemical analyses complement the interpretations. The results show a sedimentological setting of a dominantly shallow marine shelf at the transition to the slope. Some remarkable diagenetic observations are the development of replacive authigenic quartz phases during burial; the absence of evaporite phases and/or their pseudomorphs (notwithstanding their previous reporting); and the presence of under mature coal and shale in the main fault zone. The reservoir development can be explained as the result of two karst phases leading to an extensively developed karst reservoir with Namurian infills and weathered rock. Also oil migration, of which bitumen relicts have been found, might have played a role. In this study, the possibility of using Computer Tomography (CT) as a quick scan screening tool for challenging cutting material from deep boreholes was tested. Although differentiating different lithologies is roughly possible, the method failed due to the sampling conditions (containing drilling fluid, relatively large sample volume as well degree of mixing).