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Case Studies - Water and Petroleum Fluid Compositional Variations |
RWE Dea AG, Ueberseering 40, 22297 Hamburg, Germany eric.mueller{at}rwedea.com
The Voelkersen field in northwestern Germany produces thermogenic dry gas from Permian Rotliegend sandstone reservoirs located at depths greater than 4700 m. In addition to this considerable depth Zechstein salt overburden plus the structural complexity and heterogeneity of the reservoirs limit the applicability of conventional methods for definition and characterization of field compartmentalization. The Rotliegend gas is sourced from Westphalian coals of semi-anthracite to anthracite rank with conventional geochemical data suggesting little variation in composition on a field-wide scale. However, detailed analysis of associated condensates and wet-gas hydrocarbons shows considerable differences between compartments and producing horizons, despite the apparent high maturity of the gas. These differences support compartment definition and identification of lateral and horizontal seals. Assuming a quasi-uniform gas composition in communicating reservoirs, variation of carbon and hydrogen isotopic data in particular confirms separation of marginal fault blocks. Additionally, these data also suggest reservoir continuity within a large field compartment and over parts of a major fault system for which the sealing properties so far were previously uncertain.
