Oil shales: compaction, petroleum generation and expulsion

Permian to Miocene oil shales (Torbanite, Posidonia, Messel, Himmetoglu and Condor) from six basins in Australia, Germany and Turkey were studied using a variety of techniques that incorporate petrophysics, geochemistry and petrology. The objectives of this project were to improve understanding of compaction, petroleum generation and expulsion in nature as well as provide insights that may be exploited by technology for oil shale exploitation. The physical properties of the oil shales were compared to those of other oil shales from previous studies. Similar to other oil shales, grain densities ranged from 1.1g/cm³ to 2.4 g/cm³ with a strong correlation to organic matter content. Organic matter content is related to the oil shale grade used for economic assessment. The organic matter content strongly controls the behaviour of the oil shales including their mechanical properties. Existing data shows that mechanical properties are very unpredictable at high temperature especially for high-grade oil shales. The relevance of the evolution of mechanical properties at high temperature with repect to exploitation and basin modelling was investigated. Only strength can be discussed with some certainty at the moment and indicates the need for more tests to be conducted at high temperature. First indications were found demonstrating how temperature can enhance microfracturing during petroleum generation. Compaction behaviour of the six oil shales was studied under different thermo-mechanical conditions. Strength determined by compressive loading to failure at room temperature showed that the unconfined compressive strengths of the oil shales ranged from very weak to medium (5.3 to 70 MPa). Strength considered as maximum effective stress attained during burial and initial porosity (7.6 to 20.1%) showed that none could be used for burial depth estimation as suggested for organic matter-poor mudstones. Vitrinite reflectance (0.19-0.52%) limited the maximum burial to between zero and 2 km for the different oil shales. Axial strain at room temperature (1.9-23%) compared to that at 310ºC (12-79%) and 350ºC (1.38-40%) showed that temperature superceedes effective stress as the principal factor controlling mudstone deformation when rocks are rich in organic matter. Only dehydration of smectite (94-150ºC) showed a distinct contribution of mineralogy to compaction and was corroborated by X-ray diffraction. High organic matter content favours creep that is very important with increasing temperature. Transformation of organic matter characterised by the petroleum generation index was found to be a source of porosity during compaction (0.7 to 51.4%). Volume balance (2.6-12.5 % solid to liquid conversion) supported the increase in porosity experienced (1.5-6.4%) by samples after compaction. The limitation of the effective stress approach to predict porosity increase during compaction was highlighted and experiments that incorporate thermo-mechanical conditions recommended for studying compaction based on axial strain rather than porosity and void ratio change.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• Eseme, Emmanuel

Contributors dc:contributor

• Littke, Ralf

• info:eu-repo/classification/ddc/550
• Geowissenschaften
• Erdöl
• Ölschiefer
• Verdichtung, Erdöl-Erzeugung, Freisetzung
• Oil shales
• Compaction
• Petroleum Generation
• Expulsion

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123040%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:61369