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Organic geochemistry of Palaeozoic source rocks, central North Sea (CNS)

Vane, C.H.; Uguna, C.; Kim, A.; Johnson, K.; Monaghan, A.A.. 2015 Organic geochemistry of Palaeozoic source rocks, central North Sea (CNS). British Geological Survey, 100pp. (CR/15/123N) (Unpublished)

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Abstract/Summary

This report details a regional analysis of the source rock quality and potential of Palaeozoic rocks of the UK Central North Sea for the 21CXRM Palaeozoic project. The objective was to undertake a regional screening of all intervals to identify source rocks using new and legacy datasets of all Carboniferous and Devonian samples. In addition, a literature review (Appendix 1) summarises source and kerogen typing information from legacy reports. The background and stratigraphic nomenclature are given in Monaghan et al. (2016), details on individual well interpretations and stratigraphy are given in Kearsey et al. (2015). Geological context on the results of this work are included in basin modelling (Vincent, 2015) and were synthesised into a petroleum systems analysis in Monaghan et al. (2015). New and legacy Carboniferous and Devonian source rock geochemical data were examined per well using industry standard criteria to give an overview of the source rock quality, type (oil or gas prone) and maturity. The aims of this study were to classify the source rock quality of 33 wells, to examine if intervals were ‘gas-prone’ or ‘oil-prone’, and to ascertain the hydrocarbon generation stage of each well based on Rock-Eval pyrolysis, vitrinite reflectance (VR, where available) and total organic carbon (TOC) data. The term ‘gas prone’ was used to describe source rocks that have or could generate gas; ‘oil prone’ for source intervals that have or could generate oil. This study was a rapid screening exercise to identify intervals or areas of interest, and as such the data and inferences must be used concomitantly with other geological data to fully assess the source rock potential within the studied wells. It should be noted that the wells studied penetrate different parts of the geological succession and in many cases only small sections of the Devonian and Carboniferous interval. An initial sift through the wells with available geochemical data indicated that 33 wells had enough data to be usefully evaluated. Subsequently it was found that 8 of the 33 wells had incomplete, unreliable or otherwise poor source rock quality data sets and therefore were not analysed further; the reasons are detailed in this report. The remaining 25 wells selected for analysis were: 43/28-2, 26/07-1, 26/08-1, 36/13-1, 36/23-1, 38/16-1, 38/18-1, 39/07-1, 41/08-1, 42/10a-1, 42/10b-2ST, 42/09-1, 41/10-1, 42/10b-2, 41/15-1, 43/21-2, 41/01-1, 41/20-1, 41/14-1, 43/02-1, 43/17-2, 43/20b-2, 43/28-1, 43/28-2, 44/13-1, 44/16-1. Samples analysed from the majority of these wells were interpreted to be gas prone in the Carboniferous succession (Figure 1). 1. 41/10-1, 41/14-1 and 41/20-1 contained source rocks that were both gas window mature (e.g. VR >1.3) and can be regarded as excellent gas source. Strata in 43/17-2, 44/16-1 and 43/28-1 were also gas mature in all or parts of the section of interest, but with variable source rock quality. The six wells all had low S2 peaks: this may be due to either prior hydrocarbon generation and depletion or the initial presence of low amounts of non-inert kerogen. 2. 41/15-1, 42/10b-2 and 43/21-2 were also identified as possessing good gas-prone source rocks with elevated S2 values and also a high maturity attained by the source rocks. 41/01-1 was identified as a good for gas generation in the deeper section. 3. 26/07-1, 26/08-1, 36/13-1, 38/16-1, 39/07-1, 41/08-1, 42/10a-1, 42/10b-2ST, 42/09-1, 43/02-1, 43/20b-2, 43/28-2 and 44/13-1, contain good to excellent quality source rocks, but have not matured sufficiently to generate significant amount of gas, so these can be regarded as poor gas sources based on their current maturity. If present, in deeper basins some of these intervals will have generated significant quantities of gas.

Item Type: Publication - Report (UNSPECIFIED)
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This report is a published product of the 21st Century Exploration Road Map (21CXRM) Palaeozoic project. This joint industry-Government-BGS project comprised a regional petroleum systems analysis of the offshore Devonian and Carboniferous in the North Sea and Irish Sea. This report made open April 2017
Date made live: 04 Apr 2017 08:51 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/516765

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