# VARIATION OF WHOLE AND FRACTURED POROUS ROCK PERMEABILITY WITH CONFINING PRESSURE

Phenomenological models have been devised to explain the pressure variation of permeability of whole porous rocks and fractured rocks. The theory for the whole porous rock is based on the Hertz theory for the deformation of spheres by spheres. It gives permeability variations and porosity variations with pressure which have many of the characteristics noted in experimental data. The model indicates that the permeability (and porosity) will have the same variation with pressure for more than one cycle if the effective pressure is not made too high and if the porous rock is well cemented or, for non-cemented aggregates, well packed. For aggregates, the model shows an infinite slope for the pressure variation of permeability and porosity at zero-effective pressure, as is generally measured. For cemented porous rock, the model indicates that the infinite slope at zero-effective pressure will not exist. The variation of fracture permeability with pressure has been described by a "bed of nails" model to represent the asperities on the fracture face by a distribution of rods. It is shown that hemispherical, conical or wedgelike asperities can be treated by the same "bed of nails" model. Simple theoretical expressions for the fracture-permeability pressure variation are obtained if power-law distribution functions for the asperity heights are assumed. These asperity-height distribution functions should be accurate representations of the actual asperity distribution functions since they need to represent the actual distributions only over a limited range (generally less than 1/2) of the asperity heights. The use of the asperity-height distribution functions provides insight into the reason why the pressure variation of permeability is different (for the same sample) on the second loading cycle than it is on the first loading cycle. In addition, it allows one to predict what would happen on subsequent loading cycles whether the pressure variation on the first cycle is exceeded or not. A comparison of the theoretical curves with Nelson's experimental data on navajo sandstone shows excellent agreement. A favourable comparison is also made with Jones' data on fractured carbonate rocks. /TRRL/

• Availability:
• Corporate Authors:

Pergamon Press, Incorporated

Oxford OX30BW,
• Authors:
• Gangi, A F
• Publication Date: 1978-10

## Filing Info

• Accession Number: 00189666
• Record Type: Publication
• Source Agency: Transport and Road Research Laboratory (TRRL)
• Files: ITRD, TRIS
• Created Date: Jun 13 1979 12:00AM