Geochemical and Microbiological Surface Investigation in Northern Germany Indicates Interesting Hydrocarbon Potential

摘要

In 2006 RWE Dea conducted a surface-geo-chemical pilot survey in Lower-Saxony (Germany) to test surface indications of deep seated Permian-Rotliegend gases productive at over 4500 m depth within the survey area. The programme was designed as grid layout with ca. 1 km sample spacing totalling 172 sample locations. Multi-discipline analytical methods consisting of direct HC-indicators (geochemical methods) and indirect HC-indicators (microbial methods) were used to detect surface hydrocarbon signals. The applied geochemical methods used the adsorbed HC-gas characterization, iso-tope-geochemical analysis and fluorescence measurements, whereas the microbial discipline after the MPOG method detected the existence of methane and C3/C4 consuming microbes. The yields of the adsorbed HC-gases C1—C6 averaged 194 ppb with a maximum of 3551 ppb. The methane is generated from a mature marine source as analyzed from iso-tope-geochemical diagnostic. No gases of terrestrial origin were recorded above the proven producing accumulations and the remaining survey area according to isotopic analysis and the HC-gas characterization. The methane concentration of 59% indicates an oil associated gas compound. However, the MPOG method detected a prominent oil indicating "textbook" anomaly in the south eastern survey area. According to the existing seismic control the feature is located above a salt-bridge, where fractured Chalk and/or Caprock intervals at ca. 800-1000 m depth are considered as potential reservoir zones. Isotope geochemical and fluorescence characteristics in close vicinity supported the presence of a possible oil accumulation generated by mature marine source rocks. The applied multi-discipline biogeochem-ical surface-prospecting method is cost-effective and may be able to identify and con- firm subsurface HC-accumulations as an independent supplemental exploration instrument to further reduce the dry hole risk. The diagnostic results of the survey could justify a drilling test if the full geologic play could be proved.