Geochemistry of formation waters and hydrodynamic evolution of a young and restricted sedimentary basin (Mahakam Delta Basin, Indonesia)

Abstract

Chemical and isotopic data on formation waters of oil‐fields from two parallel anticline axes of the Mahakam Delta Basin provide information about the present‐day mass transfers in the sedimentary sequence of this basin. Depletions in Ca, Sr and K, enrichment in Rb, and the Sr/Ca ratios in the waters are related to illitization of smectite and precipitation of carbonate minerals, as well as dissolution of K‐feldspar and precipitation of albite. These short‐lasting processes seem to have been more pronounced in the deeper segments of the proximal anticline. The Sr, oxygen and hydrogen isotopic data emphasize occurrence of lateral migrations of the formation waters within permeable units from Borneo Island to the proximal anticline under continental influence, and further to the distal anticline under marine influence. Description of a combined process including illitization of smectite, precipitation of carbonate minerals, dissolution of K‐feldspar and precipitation of albitic feldspar, during lateral migrations of the formation waters was only possible because of the young age and the restricted volume of the basin. In addition, the chemical signatures in the formation waters were not obscured by water‐rock interactions during long‐distance migrations that occur systematically in large sedimentary basins.

Geochemical modelling of petroleum well data from the Perth Basin. Implications for potential scaling during low enthalpy geothermal exploration from a hot sedimentary aquifer

“…Secondary phases start precipitating from a pore fluid when the latter becomes saturated with these phases and a dynamic, tightly temperature dependent equilibrium between fluid and phase evolves. This principle of mineralfluid interaction reaching equilibrium, which is the basis of geothermometry (Giggenbach, 1981(Giggenbach, , 1988), has been extensively studied in sedimentary settings (Bjørlykke and Gran, 1994;Connolly et al, 1990;Furlan et al, 1995;Garrels and MacKenzie, 1972;Hanor, 1994;Hutcheon et al, 1993;Michael and Bachu, 2002;Osborne et al, 1994;Stueber and Walter, 1991;Yardley et al, 2003) and successfully applied to reconstruct in-situ compositions of sedimentary formation waters (Bazin et al, 1997;Palandri and Reed, 2001). Especially the latter of these last two references provides a detailed protocol that can be applied to the scarce chemical information of the petroleum well dataset to stitch together a consistent picture of the likely chemical composition of the geothermal waters permeating the Perth Basin.…”