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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes


AAPG Memoir 69: Previous HitReservoirNext Hit Quality Prediction in Sandstones and Carbonates, 1997
Edited by J. A. Kupecz, J. Gluyas, and S. Bloch
Pages 19-27

Prediction of Previous HitPorosityNext Hit in Compacted Sands

Jon Gluyas,1, Christopher A. Cade


We present a new Previous HitporosityNext Hit-depth relationship for clean, rigid grain (quartz, feldspar) sands under hydrostatic burial. This allows the prediction of Previous HitporosityNext Hit in uncemented sandstones to an accuracy of ±2.5 Previous HitporosityNext Hit units at 95% confidence levels. The relationship was derived using experimental data from laboratory compaction experiments and field data for buried uncemented sandstones from around the world. The equation is:

0019_u1.jpg (3,479 bytes)

where Previous HitporosityNext Hit (phi.gif (848 bytes)) is in percentages and depth (z) is in meters.

By scaling this relationship in terms of effective stress rather than depth, it can be used to provide an equally accurate prediction of Previous HitporosityNext Hit for uncemented sands in overpressured settings. This is done using the following equation:

0019_u2.jpg (3,128 bytes)

where zprime1.gif (824 bytes) = effective burial depth (in meters); z = burial depth (in meters); rho.gif (842 bytes)r = density of rock (in Kgm-3 [kilograms per cubic meter]) = typically 2650; rho.gif (842 bytes)w = density of water (Kgm-3) = typically 1050; g = gravity (in ms-2 [meters per second squared]) = 9.8; phi.gif (848 bytes)sigma.gif (843 bytes) = average Previous HitporosityNext Hit of overburden = typically 0.2; and u = overpressure (in MPa [megapascals]).

We propose that there is considerable value in a "compaction only" Previous HitporosityNext Hit-depth relationship. A compaction-only trend allows the accurate prediction of Previous HitporosityNext Hit in uncemented sandstones, and gives a maximum Previous HitporosityNext Hit baseline to which cement volumes, and resultant cemented Previous HitsandstoneNext Hit porosities, can be compared. If both cemented and uncemented Previous HitsandstoneNext Hit data are included to produce a "Previous HitporosityNext Hit loss-depth" relationship, the resultant scatter (typically ±5 Previous HitporosityNext Hit units for a given depth) in the relationship limits its usefulness.

1 Present affiliation: Monument Oil and Gas, London, United Kingdom

End_Page 19-------------------------

Prior to drilling, the new relationships may be used either to predict the Previous HitporosityNext Hit of sands that are known to be uncemented or to place an upper limit on the Previous HitporosityTop estimated for sandstones either known or suspected to be cemented.

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