Home Facts & Figures Knowledge base Gas Review of the Lower Triassic Play in the Roer Valley Graben, SE Onshore Netherlands (2012)

Review of the Lower Triassic Play in the Roer Valley Graben, SE Onshore Netherlands (2012)

This MSc this has been written former intern Roderick van der Kroef.

In the last decades extensive E&P efforts have led to a great variety of proven hydrocarbon plays and traps in the sedimentary succession of the Netherlands, both on- and offshore. The majority of the fields encountered have gas, only several small fields contain oil. The distribution of the TOC rich Posidonia shale formation of lower Jurassic (Toarcian) age clearly controlled the location of the oil fields. It has been an active source and kitchen in the West Netherlands basin, resulting in an abundance of oil fields in the Rijswijk License. The Roer Valley Graben is in fact the SE extention of this basin, although with a different burial history. It was only mildly inverted during the Sub-Hercynian tectonic pulse and has strong ongoing subsidence with tectonic activity. Currently, it is believed that the Posidonia Shale is near or at maturity level. This gives reason to believe that there may lie oil potential in the Lower Triassic play in the Roer Valley Graben. The scope of this study is to re-evaluate the available 3D and 2D seismic, well data and literature on the Roer Valley Graben to review its prospectivity, particularly focusing on oil from the Posidonia Shale and trapping style of the Main Buntsandstein Subgroup. The approach for the prospectivity review was the creation of a high resolution structural framework for the Roer Valley Graben using the structural framework module in Petrel which allows models to be built on the fly in a ‘Modeling while interpreting’ workflow. The results were a detailed 3D structural fault framework and four new detailed structural maps in elevation time of the top Posidonia Shale, base Altena Group and near top and base Main Buntsandstein Subgroup. The following step was to convert this interpretation to depth. For this purpose a hybrid velocity model was constructed which includes input from the Velmod-2 model of TNO and input calculated in Petrel from the available checkshot data. This process resulted in two detailed structural maps in depth for top and base Main Buntsandstein Subgroup. These surfaces were used in the identification of potential leads. A total of 25 leads were identified of which 7 possible oil leads, the other were identified as having gas potential. For each lead a rough estimate has been calculated for the STOIIP and GIIP. In the end a risk qualification was made based on the trap type, configuration and its location with respect to already drilled sites as well as the probability of maturity. From this classification the most promising leads were identified. These are located in fault-dip closures in the northwestern sector (lead 1, 9, 10 and 11), in a fault-dip closure south of the Waalwijk South field (lead 22) and in a down-thrown fault-dip closure in the southern sector (lead 5). From the re-evaluation it can be concluded that the juxtaposition for the Posidona Shale below the Main Buntsandstein Subgroup is not ideal and oil charge into this reservoir from this source is deemed very unlikely. However, stratigraphicly higher formations, such as the Brabant Limestones might prove successful as well as gas charge from Carboniferous Coal measures into the leads that have been identified.

A secondary objective to this study was to assess the quality of 2D lines which are reconverted from paper copies back to digital SEGY files. The conclusion of this process is that it greatly enhances the quality and usefulness of old 2D seismic data. After digitization the regenerated