Petrophysical interpretation of selected wells near Liverpool for the UK Geoenergy Observatories project

Hannis, S.; Gent, C.. 2017 Petrophysical interpretation of selected wells near Liverpool for the UK Geoenergy Observatories project. Nottingham, UK, British Geological Survey, 44pp. (OR/17/037) (Unpublished)

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This report details the petrophysical evaluation of 2 onshore wells near Liverpool UK: Kemira 1 (SJ47NE/101) and Ince Marshes 1 (SJ47NE/100). The results contribute to the geological characterisation for a monitoring experiment in Cheshire for the UK Geoenergy Observatories project. The evaluation is based on the petrophysical interpretation of available digital wireline log curve data for the two wells across the whole logged interval (according to reinterpreted stratigraphic formations defined and correlated for this project). Associated digitised sample data (XRD, XRF, TOC data) is available to help cross-validate the interpretation for 1 of the 2 wells. Outputs for this evaluation include continuous (along borehole) interpretations of clay volume, porosity, and total organic carbon (TOC). These interpreted curves were used to examine the proportions of reservoir rock and shale for each formation in each well and their respective properties. Net reservoir intervals were defined by those intervals where the clay volume was less than 50%, the porosity was more than 5% and no coal intervals were present. Net Shale intervals were defined by those intervals where the clay volume was more than 50% and no coal intervals were present. The Kemira 1 well was logged from the Triassic Bromsgrove Sandstone Formation down to the Carboniferous Westphalian A unit, the base of which is not penetrated (~1400 m logged between 32-1433 m). Data is somewhat limited compared to the Ince Marshes 1 well, comprising parts of a standard log suite, and the curve data is machine-digitised from the legacy log field prints. (Resistivity curves are only available over part of the well; the neutron log was recorded in sandstone matrix units and the specific transformation to limestone matrix units (required for the interpretation) is unknown and has been guessed at; there is less data available for this well in terms of ancillary curves or sample analysis to cross check results than for the Ince Marshes 1 well). The results of the interpretation for this well should therefore be treated with appropriate caution. The Ince Marshes 1 well was logged over the Carboniferous interval comprising the Westphalian C-A and the Millstone Grit Group, the base of which may be drilled through, but was unable to be logged due to hole difficulties (~1084 m logged between 368-1452 m). This well was drilled and logged more recently than the Kemira 1 well and has much more associated data including more advanced logging tools such as image logs, dipole sonic, and elemental spectroscopy to give formation mineral compositions. Sidewall cores were also collected and these and drill cuttings were analysed using various techniques to determine mineral, elemental and total organic carbon contents at the sample depths. There is therefore much more data available with which to cross check and verify results and as such the results of the interpretation can be regarded with a higher level of confidence than those of the Kemira 1 well. The Kemira 1 well contains strata of Permian and Triassic age. These have high reservoir net to gross (NTG) values of 0.99 or 1 (i.e. 100% net reservoir). Their average porosities range from 18- 25% and the Sherwood Sandstone Formation shows the highest average porosity at 25%. Both wells contain older, Carboniferous rocks and these have much lower NTG values, all containing less than 50% reservoir rocks (NTG ranging from 0.08-0.41). Their porosities are also lower, ranging from 8-15%, apart from the Westphalian C unit in the Kemira 1 well, which are anomalously high (23%) resulting from the presence of coal intervals and porosity artefacts adjacent to them (a software/parameter selection limitation Total organic carbon (TOC) was calculated for the rocks beneath the Westphalian B unit in the Ince Marshes 1 well. Shales with TOC values calculated as greater than 1.5 wt% were considered ‘TOC-rich’. The ratio of these to the total formation thicknesses are generally very low: 0.08-0.15 for the Westphalian A and 0.11-0.24 for the Millstone Grit. The lower end of the range is where a OR/17/037; Draft 0.1 Last modified: 2017/05/04 10:09 2 minimum shale thickness cut-off of 2 m is considered. The TOC rich shale in the Westphalian A has an average of 3.38 wt% TOC. However, individual intervals within the unit show typical curve responses for a mature source interval containing hydrocarbons and reach TOC values up to 9.18 wt%. The TOC rich shales in the Millstone Grit have an average of 2.9 wt% TOC. The TOC values measured in samples from sidewall cores and cuttings extend beneath the base of the geophysical well logs to 1575 m. There are 44 measured values averaging 2.89 wt% TOC with a maximum of 6.93 wt% TOC.

Item Type: Publication - Report (UNSPECIFIED)
Funders/Sponsors: NERC
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed. Technical appendix available for this report with permission of authors
Date made live: 19 Jun 2017 14:32 +0 (UTC)

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