80
3 PARTICLES, PORES, AND PERMEABILITY
- .... .. >. - <.~)<. <>::Z<.> <<
/
L.<::<~. >J:': ?. : .~: : <."<>.-~"?:~. ". .~.
' ~
\
Grain size
Permeability
\
)
<.
\\\ ""\ \",
"\, "'\. ""\ ""\,i '.. \
,\ ..... <<<-.t .<~--<--~q
!
Fig. 3.30. Sketches of cross-bedding to show grain-size and porosity variations. In avalanche tabular-planar
cross-bedding (upper), grain size and permeability increase down each set. In some eolian cross-bedding
(lower), foreset sands curve down into silty toesets. This correlates with a downward decrease in permeability
through each set.
number of reasons. Obviously, water flow through an aquifer will be affected by internal
permeability heterogeneities, so too will be the flow of oil and gas in a petroleum reservoir. Similarly, the permeability variations of sedimentary formations affect the flow of
mineralizing fluids. These fluids often finally precipitate ores at permeability barriers.
Considerable attention has thus been paid to the continuity of sands, and conversely
of shales, in different environments (Harris and Hewitt, 1977; Le Blanc, 1977). Mathematical methods have been devised to quantify the relationship between sand continuity and permeability. Pryor and Fulton (1976) have devised the lateral continuity index
(LCI) and the vertical continuity index (VCI) as significant parameters of sedimentary
deposits. To calculate the LCI a series of cross-sections is drawn. Maximum and minimum sand continuity are measured and divided by the section lengths. The VCI is calculated by measuring the aggregate sand thickness at various locations and dividing it
by the thickness of the thickest sands. In a study of Holocene sands of the Rio Grande,
Pryor and Fulton (1976) found wide ranges of continuity when comparing fluvial,
fluviomarine, and pro-delta deposits. Weber (1982) has approached the problem from
the opposite direction, compiling data on shale continuity in various environments
(Fig. 3.32).
Earlier in this chapter, we mentioned that one should note the different volumes of
sediment whose porosity or permeability is measured by different techniques, ranging
from thin section to seismic. In conclusion one should now also note the hierarchy of
different heterogeneities encountered in sedimentary rocks (Fig. 3.33). This chapter
has mainly described the controls on microscopic heterogeneities, and at its conclu-
3 PARTICLES, PORES, AND PERMEABILITY
- .... .. >. - <.~)<. <>::Z<.> <<
/
L.<::<~. >J:': ?. : .~: : <."<>.-~"?:~. ". .~.
' ~
\
Grain size
Permeability
\
)
<.
\\\ ""\ \",
"\, "'\. ""\ ""\,i '.. \
,\ ..... <<<-.t .<~--<--~q
!
Fig. 3.30. Sketches of cross-bedding to show grain-size and porosity variations. In avalanche tabular-planar
cross-bedding (upper), grain size and permeability increase down each set. In some eolian cross-bedding
(lower), foreset sands curve down into silty toesets. This correlates with a downward decrease in permeability
through each set.
number of reasons. Obviously, water flow through an aquifer will be affected by internal
permeability heterogeneities, so too will be the flow of oil and gas in a petroleum reservoir. Similarly, the permeability variations of sedimentary formations affect the flow of
mineralizing fluids. These fluids often finally precipitate ores at permeability barriers.
Considerable attention has thus been paid to the continuity of sands, and conversely
of shales, in different environments (Harris and Hewitt, 1977; Le Blanc, 1977). Mathematical methods have been devised to quantify the relationship between sand continuity and permeability. Pryor and Fulton (1976) have devised the lateral continuity index
(LCI) and the vertical continuity index (VCI) as significant parameters of sedimentary
deposits. To calculate the LCI a series of cross-sections is drawn. Maximum and minimum sand continuity are measured and divided by the section lengths. The VCI is calculated by measuring the aggregate sand thickness at various locations and dividing it
by the thickness of the thickest sands. In a study of Holocene sands of the Rio Grande,
Pryor and Fulton (1976) found wide ranges of continuity when comparing fluvial,
fluviomarine, and pro-delta deposits. Weber (1982) has approached the problem from
the opposite direction, compiling data on shale continuity in various environments
(Fig. 3.32).
Earlier in this chapter, we mentioned that one should note the different volumes of
sediment whose porosity or permeability is measured by different techniques, ranging
from thin section to seismic. In conclusion one should now also note the hierarchy of
different heterogeneities encountered in sedimentary rocks (Fig. 3.33). This chapter
has mainly described the controls on microscopic heterogeneities, and at its conclu-