(n.) Drilling Fluids. A laboratory test used to determine if a drilling fluid blocks movement of filtrate through pore spaces of a shale sample. The PPT device monitors the increase in pore pressure in a shale when exposed to a drilling fluid over a period of time. Shale cores from 1 to 3-inches long are fitted into a modified Hassler cell that has sensitive pressure transducers in reservoirs on each end of the cell. Alt. form: PPT