•Drilling fluids are slurries composed of a liquid phase and solid particles.
–Filtration refers to the liquid phase of the drilling mud being forced into a permeable formation by differential pressure.
–During this process, the solid particles are filtered out, forming a filter cake
•Mud systems should be designed to seal permeable zones as quickly as possible with thin, slick filter cakes.
–In highly permeable formations with large pore throats, whole mud may invade the formation (depending on the size of the mud solids).
–In such situations, bridging agents must be used to block the openings so the mud solids can form a seal. Bridging agents should be at least one-half the size of the largest openings.
–Such bridging agents include calcium carbonate, ground cellulose and a wide variety of other lost-circulation materials
•Filtration occurs under both dynamic and static conditions during drilling operations.
–Dynamic tests are normally run in a laboratory environment using equipment such as a Fann 90
–Static test are run in the field and include the standard API filter press and the HPHT filter press
•For filtration to occur, three conditions are required:
–A liquid or a liquid/solids slurry fluid must be present.
–A permeable medium must be present.
–The fluid must be at a higher pressure than the permeable medium.
•Factors affecting filtration
–Time
–Pressure differential
–Filter cake permeability
–Viscosity
–Solids
•Orientation and composition
•Dynamic Filtration
–Dynamic filtration is significantly different from static filtration, often with considerably higher filtration rates.
–No direct correlation exists between API and HTHP static filtration measurements and dynamic filtration.
–Experience has shown that a mud which exhibits good static filtration characteristics and stability will have satisfactory performance under actual drilling conditions, indicating the dynamic fluid loss is in a satisfactory range.
–Filtration refers to the liquid phase of the drilling mud being forced into a permeable formation by differential pressure.
–During this process, the solid particles are filtered out, forming a filter cake
•Mud systems should be designed to seal permeable zones as quickly as possible with thin, slick filter cakes.
–In highly permeable formations with large pore throats, whole mud may invade the formation (depending on the size of the mud solids).
–In such situations, bridging agents must be used to block the openings so the mud solids can form a seal. Bridging agents should be at least one-half the size of the largest openings.
–Such bridging agents include calcium carbonate, ground cellulose and a wide variety of other lost-circulation materials
•Filtration occurs under both dynamic and static conditions during drilling operations.
–Dynamic tests are normally run in a laboratory environment using equipment such as a Fann 90
–Static test are run in the field and include the standard API filter press and the HPHT filter press
•For filtration to occur, three conditions are required:
–A liquid or a liquid/solids slurry fluid must be present.
–A permeable medium must be present.
–The fluid must be at a higher pressure than the permeable medium.
•Factors affecting filtration
–Time
–Pressure differential
–Filter cake permeability
–Viscosity
–Solids
•Orientation and composition
•Dynamic Filtration
–Dynamic filtration is significantly different from static filtration, often with considerably higher filtration rates.
–No direct correlation exists between API and HTHP static filtration measurements and dynamic filtration.
–Experience has shown that a mud which exhibits good static filtration characteristics and stability will have satisfactory performance under actual drilling conditions, indicating the dynamic fluid loss is in a satisfactory range.
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