BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
mineralogical type produces a characteristic spectrum. With the help of a collection of spectra,
mineral structures can be identified.
Table 2-3
Typical Mineralogical Analysis of Norway Shale
Mineral Component Percentage
Quartz 10 - 15
Feldspar 1 - 2
Calcite
Trace
Pyrite 1 - 2
Illite 10 - 15
*Mixed Layer 35 - 40
Kaolinite 15 - 20
Chlorite 3 - 5
* Mixed layer clays have 25% to 50%
expandable layers
Sandstone
Composition and Characteristics
Sandstone bodies are formed in a large variety of environments and acquire a variety of shapes and
characteristics. Because sandstone is deposited virtually everywhere, it occurs most often as a
reservoir rock.
Sandstone is composed of sand-sized particles, ranging in size from 1/16 mm to 2 mm, that have been
compacted or cemented together. Its size relative to other clastic sedimentary rocks (rocks composed
of clasts, which are fragments or grains of pre-existing rock) is shown in table 2-4.
Table 2-4 Clastic Sedimentary Rocks
Sediment Size Rock
Gravel > 2 mm Conglomerate
Sand 2 to 1/16 mm Sandstone
Silt 1/16 to 1/256 mm Siltstone
Clay < 1/256 mm Shale
Sorting of sandstone particles ranges from good to poor in a rock that can be designated as coarse,
medium or fine within the size range for sandstone. Since sandstone fragments can be of virtually any
composition, sandstone rock itself can be designated according to its mineral composition or its
combination of constituents. Examples are:
• Quartz sandstone, consisting of resistant quarts grains
• Felspathic or Arkosic sandstone with more than 20% feldspar grains
• Greywacke, consisting of poorly-sorted grains with abundant feldspar
• Clay matrix, some of which may be altered to chlorite
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 2-9