Permeability per unit thickness of a static (not in motion) shale-shaker screen. NOTE It is expressed in units of kilodarcies/millimetre. The darcy is not an SI unit. The SI unit of permeability to fluid flow is defined as the amount of permeability that permits 1 m3 of fluid of a viscosity of 1 pascal per second to flow through a section 1 m thick with a cross section of 1 m2 in 1 second at a pressure difference of 1 pascal. That unit has no special name. The SI unit of permeability = 1,013 25 × 1012 darcy.
Source: API RP 13C, Recommended Practice on Drilling Fluids Processing Systems Evaluation, Upstream Segment, Fourth Edition, December 2010. Global Standards