Maturity modelling of selected wells in the Orcadian Study Area

Vincent, C.J.. 2016 Maturity modelling of selected wells in the Orcadian Study Area. British Geological Survey, 61pp. (CR/16/036N) (Unpublished)

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This report details maturity and migration modelling of four wells for the 21CXRM Palaeozoic project, Orcadian study area. The aim of the maturity modelling was to predict if Devonian and Carboniferous source rock intervals within the wells are, or have been, mature for hydrocarbon generation. Wells 12/27- 1 and 20/10a- 3 were chosen for 1D modelling based on availability of maturity and geochemical data (Figure 1). As this region comprises a series of Palaeozoic structural highs and basins, two wells cannot fully represent the geological evolution of the study area. Two ‘scenario’ or ‘pseudo’ wells, 12/16- 1 and 21/06b- 5 were included to contrast the basin history. Previous basin modelling work in the Inner Moray Firth is summarised in Greenhalgh (2016) and this study is placed in regional context in Monaghan et al. (2016). Inner Moray Firth (IMF) Lacustrine strata deposited during Lower and Middle Devonian times are believed to offer the main source rock potential in the IMF (see summary in Greenhalgh, 2016), as the high TOC Jurassic strata are largely immature (Fraser et al., 2003, their fig. 17.2). Well 12/27- 1 is situated on a post-Lower Devonian relative high (Figure 2), has moderate/good Total Organic Content (TOC) in the Lower Devonian Struie Formation and oil and gas shows are observed (well report; Vane et al., 2016). Two cases were modelled to accommodate uncertainty in the maturity data, with a significant impact on the timing of generation. If deepest burial was achieved during Devonian times (fitted to higher maturity values; Figure 13, 14, 15), then main hydrocarbon generation occurred during Devonian burial (Figure 17). However, if deepest burial occurred during Cretaceous – Cenozoic times (best fit to maturity values, though these data are possibly supressed; Figure 5, 7, 8) then generation occurred from the Struie Formation during both Devonian and Cretaceous – Cenozoic times (Figure 9). Please see Section 4 for more detail. Carboniferous strata are rarely penetrated by wells in the IMF. The anomalous Firth Coal Formation to Devonian succession proven in Well 12/16- 1, close to the Great Glen and Wick faults was modelled (Figure 21, 24). Well 12/16-1 lies in a different Palaeozoic sub-basin to Well 12/27-1. It is classed as a ‘scenario’ well due to uncertainties in the constraining data. The source rock intervals contain mainly gas prone kerogens and as the Carboniferous strata only reached the main oil maturity window during deep Carboniferous burial, significant gas generation is not expected. Given the block and basin structure of the IMF during the Palaeozoic Era and the variable distribution of facies, any single well is unlikely to provide a complete representation of the geological history and petroleum systems. The model results are useful in assessing the maturity geohistory and generation potential of the region, but must be considered in the regional context of the Orcadian study area (see Monaghan et al., 2016). South Buchan Basin Well 20/10a- 3 was drilled on a high at the western margin of the South Buchan Basin and was chosen for modelling based on availability of maturity data. The Firth Coal Formation source rocks are interpreted to be mainly gas prone but some condensate prone intervals were noted towards the bottom of the drilled interval. The 1D basin modelling shows that the Firth Coal Formation reached the mid mature window for oil generation during deep Cenozoic burial (Figure 288, 30, 31, 32).

Item Type: Publication - Report
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 Roadmap (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: 03 Apr 2017 11:33 +0 (UTC)

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