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The Ensign enigma: improving well deliverability in a tight gas reservoir

K. Purvis, K. E. Overshott, J. C. Madgett and T. Niven
Geological Society, London, Petroleum Geology Conference series, 7, 325-336, 1 January 2010, https://doi.org/10.1144/0070325
K. Purvis
Venture Production plc, Kings Close, 62 Huntly Street, Aberdeen AB10 1RS, UK (e-mail: )
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  • For correspondence: katie.overshott@centrica.com
K. E. Overshott
Venture Production plc, Kings Close, 62 Huntly Street, Aberdeen AB10 1RS, UK (e-mail: )
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  • For correspondence: katie.overshott@centrica.com
J. C. Madgett
Venture Production plc, Kings Close, 62 Huntly Street, Aberdeen AB10 1RS, UK (e-mail: )
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  • For correspondence: katie.overshott@centrica.com
T. Niven
Venture Production plc, Kings Close, 62 Huntly Street, Aberdeen AB10 1RS, UK (e-mail: )
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  • For correspondence: katie.overshott@centrica.com
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Abstract

The Ensign Gas Field is located in the Sole Pit basin in the Southern North Sea. The reservoir is the Rotliegend Group Leman Sandstone Formation of Lower Permian age and comprises sediments deposited in an arid continental environment. The main gas-bearing interval in the field consists of sabkha, waterlain and minor aeolian sands, reflecting deposition in an erg margin/lake margin setting. The poor primary reservoir quality of these sands has been severely reduced by extensive illite cementation resulting in average air permeabilities of <1 mD. Attempts to develop the field economically utilizing fracture‐stimulated vertical wells has met with mixed results, with flow rates of 14 MMscf per day and lower being measured during testing. The most recent appraisal well drilled on the field was a long horizontal well that was stimulated with five hydraulic fractures resulting in an economic flow rate of 44 MMscf per day. Analysis of the core and log data acquired during the appraisal of the field has shown that the reservoir contains a heterogeneous distribution of fractures, faults and micro-faults. The fracture population is dominated by conductive north–south striking fractures, with subordinate NNW–SSE resistive fractures and NE–SW mixed fractures that are arranged in clusters, with zones of high and low fracture density. Well results to date suggest that the NE–SW open and partially open fractures observed in core do not improve reservoir productivity, but those orientated north–south that are conductive appear to improve well deliverability.

Keywords
  • Rotliegend
  • Leman Sandstone
  • illite cementation
  • fracture stimulation
  • © Petroleum Geology Conferences Ltd. Published by the Geological Society, London
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Geological Society, London, Petroleum Geology Conference 				series: 7 (1)
Geological Society, London, Petroleum Geology Conference series
Volume 7
2010
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The Ensign enigma: improving well deliverability in a tight gas reservoir

K. Purvis, K. E. Overshott, J. C. Madgett and T. Niven
Geological Society, London, Petroleum Geology Conference series, 7, 325-336, 1 January 2010, https://doi.org/10.1144/0070325
K. Purvis
Venture Production plc, Kings Close, 62 Huntly Street, Aberdeen AB10 1RS, UK (e-mail: )
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: katie.overshott@centrica.com
K. E. Overshott
Venture Production plc, Kings Close, 62 Huntly Street, Aberdeen AB10 1RS, UK (e-mail: )
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: katie.overshott@centrica.com
J. C. Madgett
Venture Production plc, Kings Close, 62 Huntly Street, Aberdeen AB10 1RS, UK (e-mail: )
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: katie.overshott@centrica.com
T. Niven
Venture Production plc, Kings Close, 62 Huntly Street, Aberdeen AB10 1RS, UK (e-mail: )
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: katie.overshott@centrica.com

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The Ensign enigma: improving well deliverability in a tight gas reservoir

K. Purvis, K. E. Overshott, J. C. Madgett and T. Niven
Geological Society, London, Petroleum Geology Conference series, 7, 325-336, 1 January 2010, https://doi.org/10.1144/0070325
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  • Article
    • Abstract
    • Field history
    • Structure and tectonic setting
    • Stratigraphy
    • Reservoir sedimentology
    • Reservoir structure
    • Seismic interpretation
    • Field appraisal Phase I
    • Appraisal Phase II
    • Discussion: the potential role of naturally occurring fractures on productivity in tight gas reservoirs
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