Onshore Shale Gas Potential of the Lower Jurassic Althena Group (2010)

Deze MSc scriptie is geschreven door oud-stagiair Laurens Kee.

Global demand for fossil fuels rises every day as the world population and its standard of living increase. For decades, the Netherlands have had the privilege to provide part of Western Europe with natural gas, contributing to the national economy with its resulting profit. In 2009, Dutch gas production was over 70 billion cubic metres (BCM), of which 37 BCM came from the Groningen field.

At the present day however, most conventional gas fields have already been located and put into production, and only few significant prospects remain. Even the giant Groningen field is nearing depletion. Consequently, the Netherlands will have to find new, unconventional, gas resources or face losing their economic role as gas producer. One such unconventional resource is shale gas, gas trapped in its shale source rock. Following the great success of the North American Barnett shale, oil companies worldwide have gained interest in this new, high-potential reservoir.

In the Netherlands, two onshore shale strata occur that have potential for shale gas: the Lower Jurassic Altena Group, including the Posidonia shale, and the Lower Namurian Geverik member. For the Geverik member, very few data are available. This makes defining its potential difficult. Therefore, this thesis focuses on the Lower Altena group of the West Netherlands Basin and Roer Valley Graben, comprising the Posidonia Shale, Aalburg and Sleen formation.

In this study, the experience from successful plays in other parts of the world is combined with regional log data to investigate the potential of each formation. Additionally, shale cores were pyrolysed for TOC content and kerogen, and analysed for bulk mineralogy and clay-content by Qemscan. Five Jurassic cores were also subjected to adsorption measurements, which are one of the first adsorption measurements ever performed for Dutch substrata.

From the various data sources, it appeared that on average the Posidonia formation is the formation with the highest potential for shale gas, despite its low maturity. Its substantial thickness, TOC content, wide-spread occurrence, and high gas shows make it a formation with good shale-gas prospects. The Aalburg and Sleen formation are found to be of less importance. This is mainly due to the low TOC content of both formations. However, significant gas shows in mainly the western part of the Netherlands suggest that these formations have more potential than TOC level suggests.

Areas with the highest shale-gas potential (so-called sweet spots) have been identified for each formation. Although an estimate of gas-in-place is made using all measured and analysed parameters, production potential does not only depend on whether or not the gas is physically in place, but also on factors such as technical feasibility, environmental impact, political stance toward fossil fuels, and economic conditions. This thesis however states that all three formations contain sweet spots that may be of economic importance. It is therefore recommended that the study of these spots is continued in order to assess their development. It is recommended that the focus of such a study should be in the region between the cities of Utrecht and Tilburg, where a major sweet spot for the organically-enriched Posidonia shale overlaps sweet spots for the Aalburg and Sleen formation.