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STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

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Drilling Muds and Completion Fluids 703<br />

Table 4-60<br />

Drillina Fluids: Problems in Intermediate Drillina<br />

SHALES<br />

MLT OR SALT WATER<br />

BEARING FOlMATlONS<br />

______<br />

SILTSTONE<br />

SAND<br />

ANHYDRITE AND<br />

GYPSUM<br />

?RACTUIED FORMATION2<br />

AND CONGLOMERATES<br />

Loy drruhlloa.<br />

<strong>GAS</strong> AND OIL BEARING<br />

FORMATION8<br />

The invasion of particles can be eliminated either by using solids-free systems<br />

or by formation of a competent filter cake on the rock surface. If the components<br />

forming the filter cake are correctly chosen and blended, they will form<br />

a very effective "downhole" filter element. This ensures that colloidal sized clays<br />

or polymeric materials are retained within the filter cake and do not enter the<br />

formation. Further protection is provided by ensuring that a thin filter cake is<br />

formed due to low dynamic and static filtrate losses. Thus, the cake may be easily<br />

removed when the well is brought into production. Additionally, the filter cake<br />

can be soluble in acid or oil.

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