Отправлено: 15.11.12 17:23. Заголовок: Using NMR Logs to Enhance Permeability Estimates in Siderite Rich Intervals

AAPG Annual Meeting
March 10-13, 2002
Houston, Texas
Edwin H Westergaard, Raymond L Eastwood, Austin Boyd. Greg Gubelin(1) BP Alaska, Anchorage, AK (2) Schlumberger-Doll research, Ridgefield, CT (3) Schlumberger,
Oklahoma City, OK

Using NMR Logs to Enhance Permeability Estimates in Siderite Rich Intervals at Aurora and Borealis, North Slope Alaska Satellite Fields
Aurora and Borealis are North Slope Lower Cretaceous Kuparuk Formation satellite fields
with combined estimated reserves over 130 MMBO. The Kuparuk C, the primary reservoir
at Aurora/Borealis, contains significant siderite and glauconite. NMR logs are being used
to help improve permeability estimates in constructing a 3D Geocelluar Model. This model
will be the foundation for reservoir simulation.
A key challenge to petrophysical interpretation and building a geologic model has been the
effect of complex lithology on log-computed permeability. NMR log permeability and
measured core permeability show close agreement except in sideritic zones. The
presence of siderite causes a significant shift in the NMR T2 relaxation times and a
subsequent decrease in NMR log permeability estimation. The shift to faster T2 relaxation
time is primarily due to iron content in the siderite. NMR total porosity is unaffected by
siderite. Adjustments can be made to NMR log processing parameters for improved
permeability and capillary bound fluid estimation. Core comparisons demonstrate, in
sideritic intervals, NMR logs can provide a more accurate total porosity than conventional
neutron-density cross-plot porosity. Siderite content can then be determined from variation
between NMR total porosity and density porosity in sideritic zones. Using this technique,
adjustments can be made to NMR processing and interpretation parameters in sideritic
zones to provide more accurate permeability estimation and capillary bound fluid
determination. Lab NMR on selected siderite rich cores was performed to verify this
technique.
Comparisons between NMR T2 cut-off, surface relativity and internal field gradient vs. siderite content will be presented.
http://www.searchanddiscovery.com/abstracts/pdf/2002/annual/SHORT/ndx_41334.pdf