Bernhard Cramer¹, Peter Gerling¹, Eckhard Faber², Roland Gaschnitz³, Bernd M. Krooss³
(1) Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany
(2) Federal Institute for Geosciences and Natural Resources (BGR)
(3) Aachen University of Technology (RWTH), Aachen, Germany

Abstract: Pre-Drilling Quality Prediction of Reservoir Contents from Geochemical Modelling of Natural Gas - New Approaches based on Molecular and Isotope Kinetics

Gas and isotope geochemical data, together with other geoscientific information, is the key to understanding reservoir development of natural gas accumulations. During the last three decades, geochemists have developed various techniques and interpretation tools for the genetic characterisation of natural gas, for correlating gas with source rocks, for understanding of migration and secondary fractionation processes, and for surface geochemistry. These interpretation tools use chemical and isotopic compositions of natural gas. While the numerical description of natural gas generation by chemical reaction kinetics is state of the art and widely applied in basin modelling programs, the interpretation of the isotopic composition of gas components still largely relies on empirical relationships. For example, these relationships are used to deduce from stable carbon isotope ratios of individual light hydrocarbons the type and maturity of the source rock.

Using a new analytical approach - a combination of dry, open-system pyrolysis with stable isotope mass spectrometry (IRMS) - natural gas generation from coal and the associated isotope fractionation has been investigated in detail. Based on the experimental results a reaction kinetic model of isotope fractionation during natural gas generation has been developed.

Applying this new model to data from producing gas fields in the Northwest European Basin it is demonstrated that the timing of reservoir filling can be reconstructed even under complex geological conditions including tectonic inversion. Moreover, taking into consideration a specific geological setting it is possible to predict gas quality for structures to be drilled.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana