Analysing Overpressure Distributions within Palaeogene Strata of the Central North Sea

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1 Analysing Oerpressure Distributions within Palaeogene Strata of the Central North Sea Jenna Robertson Department of Earth Science, Uniersity of Durham

2 Aims Use aailable pressure data from wells to map regional ariations in oerpressure Determine directions of fluid flow and possible connectiity between Palaeogene reseroirs Locate areas with the potential for hydrodynamic trapping

3 Study Area OUTER MORAY FIRTH CENTRAL GRABEN

4 Data Aailability Total of 331wells UK (308) Norway (19) Denmark (4)

5 Methodology UK 15/29a-9 Forties Sandstone Member 16 psi Oerpressure Balmoral Sandstone Unit Constant Hydrostatic gradient Andrew of Sandstone psi/ft Unit

6 Methodology 32 psi Oerpressure UK 15/29a-9 19 psi Forties Sandstone Member GWC Balmoral Sandstone Unit Hydrocarbon down to points Reseroirs containing hydrocarbons only Proide estimate of the maximum Andrew Sandstone Unit oerpressure in aquifer below

7 Methodology Quaternary MONTROSE MORAY STRONSAY NORDLAND Total 482oerpressure NORDLAND GP Pliocene points Miocene Oligocene Each alue assigned Brodie HORDA to FM Eocene the corresponding Caran reseroir unit according Tay to the lithostratigraphic nomenclature BALDER of Knox FM and Holloway (1992) Palaeocene MOUSA FM DORNOCH FM Sele sands LARK FM Forties SELE FM Mey LISTA FM MAUREEN FM Some oerpressure alues were collected from within lower permeability shale units

calibrated where aailable with seismic data and biostratigraphic

8 Reseroir Distribution Reseroir distribution was based on ealuation of wireline log data from 664 Central North Sea wells calibrated where aailable with seismic data and biostratigraphic data Tay Sand Isochron (TWT)

9 Reseroir Distribution Additionally sources such as the Ternan Ltd Reports, Millennium Atlas and arious other published literature were also used

Mey Sandstone Oerpressure (psi) -100 0 500 1000 1500 2000 2500

recorded in Quad 30/8 Laterally draining NW towards the Moray

10 Mey Sandstone Oerpressure (psi) oerpressure points Max alues of oerpressure ~ 2500 psi recorded in Quad 30/8 Laterally draining NW towards the Moray Firth Steep pressure ramp with implications for hydrodynamics Flyndre field

Forties Sandstone Oerpressure (psi) -100 0 500 1000 1500 2000 2500 145 oerpressure points Max alue of oerpressure recorded is ~1300 psi in UK

11 Forties Sandstone Oerpressure (psi) oerpressure points Max alue of oerpressure recorded is ~1300 psi in UK 30/8 Magnitude of oerpressure not as great as the Mey Sandstone Main flow direction SE to NW, with drainage also occurring towards the western margin

12 Forties Sandstone 145 oerpressure points Max alue of oerpressure recorded is ~1300 psi in UK 30/8 Magnitude of oerpressure not as great as the Mey Sandstone Main flow direction SE to NW, with drainage also occurring towards the western margin (Dennis et al. 2000)

Upper Sele Sands Oerpressure (psi) 0 50 100 150 200 250

13 Upper Sele Sands Oerpressure (psi) oerpressure points Maximum of 336 psi Minimum of 29 psi

14 Tay Sandstone ~ 3250 ft (TVSS) Oerpressure (psi) 0 50 UK 21/29a psi OP in Tay TAY 52 oerpressure points Maximum of 72 psi Minimum of 10 psi

15 Residuals Residual alues of oerpressure are the difference in oerpressure between reseroir units Residuals were calculated between each adjacent reseroir unit to help identify areas of ertical connectiity Calculated using the deeper reseroir oerpressure minus the shallower reseroir oerpressure B A = +e POSITIVE RESIDUAL Oerpressure B > Oerpressure A +e oerpressure difference Pressure Transition Zone Redcolour on maps

16 Residuals B A = - e NEGATIVE UK 21/29a-8 RESIDUAL Oerpressure A > Oerpressure B -e oerpressure difference Pressure Reersal Bluecolour on maps B A = zero ZERO RESIDUAL Oerpressure A = Oerpressure B Zero oerpressure difference (+/- 10psi) Reseroir units hae the same oerpressure, they are in pressure connection Neutralcolour on maps

17 Mey-Forties Residual Residual (psi)

18 Forties-Upper Sele Residual Residuals range from -40 to +130 psi

19 Upper Sele-Tay Residual Residuals range from -20 to +20

20 Conclusions The Mey Sandstone Member and Forties Sandstone Members are laterally draining SE NW with additional drainage in the Forties to the western margin Although only weakly oerpressured the Upper Sele and Tay sandstone units also appear to be laterally draining towards the western margin Residual alues indicate that there is oerall good connectiity between sands towards the western margin (Quad 21), which may be a result of faulting or injectites Further work on structure is needed to support interpretations

21 Any Questions? Special thanks to sponsors Maersk Oil Aberdeen and GeoPressure Technology Ltd, Ternan Ltd for supplying Palaeogene play maps and IHS for supplying pressure data

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