High Temperature Methane
High maturity source rocks generate gas, but we now know that not all source rocks generate gas at the same level of thermal stress. Organic-rich marine type II source rocks generate secondary gas from unexpelled oil during the second half of catagenesis, beginning at the relatively low maturity of Ro >1.2%. In contrast, shales containing a mixture of marine and terrigeneous phytoclasts generate most of their gas at much higher maturity levels (Ro > 2.0%). This late gas originates neither from kerogen (primary) nor from unexpelled oil (secondary) but from a neoformed recombination residue generated at lower maturation levels.
Within the project we examine a series of immature source rocks and natural maturity sequences from our worldwide sample base and additional samples provided by sponsors to find out how the formation of this late gas potential is a function of organic matter evolution and depositional environment. Using open- and closed-system pyrolysis we document stable isotope characteristics for formed hydrocarbons within these systems and build a kinetic model for primary and secondary gas generation. Additionally, residues will be characterised using pyrolysis, isotopic and spectroscopic methods to investigate directly compositional changes of the initial kerogen structure and early formed bitumen.
The work has immediate application in both conventional and unconventional gas plays. Shale gas “sweet spots”, for instance, are strongly controlled by secondary gas occurrence.
- B. Horsfield
- N. Mahlstedt
Partners and Sponsors
Shell, Eni, Devon, Total, Petrobras, Wintershall, Maersk