Print Email Facebook Twitter Generation, migration, entrapment and leakage of microbial gas in the Dutch part of the Southern North Sea Delta Title Generation, migration, entrapment and leakage of microbial gas in the Dutch part of the Southern North Sea Delta Author Verweij, J.M. Nelskamp, S.N. ten Veen, J.H. de Bruin, G. Geel, K. Donders, T.H. Publication year 2018 Abstract Understanding the shallow gas system is critical for assessing its potential as an energy source, for evaluating the possible hazard of shallow gas for drilling and wind farm locations and for evaluating the effect of gas emissions at the seabed on marine ecosystems and climate. This paper presents the key elements and processes of the microbial shallow gas system in the Plio-Pleistocene Dutch Southern North Sea Delta based on recent findings from different projects. Geochemical and carbon isotopic composition of shallow gas occurrences in the delta are indicative of a microbial origin of the gas. Shallow gas mainly occurs in stratigraphic traps and stacked anticlinal structures above salt structures, as indicated by identified direct hydrocarbon indicators on seismic, such as bright spots. Organic matter in the delta deposits is of predominantly land plant origin with TOC values varying between <1% and 5%, and mostly between 1 and 2%. Simulations of temperature and burial history in combination with dedicated 1D simulations of microbial gas generation reveal that gas generation in the delta started in Early Pleistocene Calabrian times and is still ongoing. Simulated volumes of gas generation are more than enough to fill published estimated volumes of shallow gas prospects in the delta. The geometry of the E-W prograding delta sequences and the close interbedding of interglacial silty/sandy and glacial clayey/silty sediments focus gas migration updip through the foresets towards the topsets of the delta sequences, and ultimately into the anticlinal stacked traps. Grain-size based calculations of the permeability and capillary seal capacity of clayey/silty seals of the stratigraphic and anticlinal traps provided first estimates of permeability values ranging from 2.8E-20 m2 to 1.1E-18 m2 and capillary seal capacity values between 10m and 24m. Comparison of gas column heights derived from grain-size based calculations, cross plots of neutron and density logs and pressure measurements, with trap heights derived from seismic bright spots suggests that many traps in stacked bright spots are not filled to structural spill point. This suggests that filling of the stacked reservoirs is not related to fill-spill migration, but rather to leakage through the top seal. In absence of fault and fracture zones crossing the seal, this leakage is related to the capillary seal capacity and permeability of the top seal. The leakage extends, locally, to the seabed. The microbial gas system in the delta today is a highly dynamic system driven by ongoing burial of the delta sediments and microbial gas generation. © 2018 Subject Geological Survey NetherlandsGeosciences2015 EnergyCapillary seal capacityGas generation modellingMicrobial gas systemSouthern north sea delta To reference this document use: http://resolver.tudelft.nl/uuid:72a6cbee-a500-4928-a6e0-0dbd1760c597 DOI https://doi.org/10.1016/j.marpetgeo.2018.07.034 TNO identifier 842178 Publisher Elsevier Ltd ISSN 0264-8172 Source Marine and Petroleum Geology, 97, 493-516 Document type article Files To receive the publication files, please send an e-mail request to TNO Library.