STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

694 Drilling and Well Completions
Table 4-57
Specific Gravity of Liquids and Solids in Mud [29]
Material
Anhydrite
Barite"
Calcite
Chlorite
Dolomite
Galena
Gypsum
Hematite
Illite
Lignite
Limestone
Montmorillonite
Pyrite
Quartz
Sodium Chloride
Sulfur
Water
'Chemically pure
Specific
Gravity'
2.95
4.45
2.71
2.71
2.85
7.50
2.32
5.26
2.84
1.10
2.69
2.35
5.06
2.65
2.1 65
1.96
1 .oo
Composition
NaCl
Solids in Unweighted Muds
Solids in unweighted muds include viscosifers and drilled solids. The most
expensive portion of unweighted muds are the liquids and colloidals. The
main concern in unweighted muds is to keep mud weight as low as possible
and to maintain flow properties. Thus, viscosifers are added as needed
to unweighted muds to control filtration, to suspend solids, and to provide
the properties necessary to clean the borehole. The detrimental solids in
unweighted muds are those of ultrafine size and larger, produced by the
bit. It is essential to have a good solids removal system to prevent solids
dispersion and mud density buildup. Size and range of solids in unweighted
muds are shown in Figure 4-117 [29].
Solids in Weighted Muds
Solids in weighted muds consist of viscosifers, weighting material, and drilled
cuttings. The most expensive portion of weighted mud is the weighting material.
The main problem related to solids control is the prevention of viscosity increase
caused by accumulation of colloidal drilled solids. Chemical treatment can be
used initially to control this viscosity, but it becomes ineffective as colloidal
solids in the mud increases. Eventually, mud dilution and mechanical removal
of solids are needed. The size range of solids in a weighted mud is illustrated
in Figure 4-118 [29].
Figure 4-119 through 4-122 can be used to evaluate the extent of drilled solids
contamination [25].