Fluid lossmudcake

As the hydrostatic head of the mud is generally higher than the pore pressure in the formation, liquid from the mud will be forced into the formation. Consequently a filtercake consisting of the solids in the mud is formed on the borehole wall. For various reasons it is essentia! that this mudcake is as thin and impermeable as possible. Dispersed and deflocculated clay particles are very small and flat and can form a thin and impermeable mudcake. If larger particles are present (clay aggregates, flocculated clay, sand, weighting material) the space between the particles in the mudcake is bigger and various chemicals are required to control the fluid loss

The fluid loss is determined according to an API method and expressed in ml/30 min. Local experience is required to establish the fluid loss requirements for particular hole intervals. The condition and thickness of the filtercake obtained from the API test are very important for e.g. sticking tendency of the hole.

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