Piezometric Surface The imaginary surface to which groundwater rises under hydrostatic pressure in wells or springs.

Proppant Sand-sized solid grains that are injected in a fluid suspension and used to hold open stimulated fractures in a geothermal reservoir.

Propylitic Alteration A term borrowed from studies of hydrothermal ore deposits that refers to an assemblage of secondary hydrothermal minerals which forms in igneous rocks. This assemblage...