1. n. [Geophysics]

An area in which water is too shallow for acquisition of marine seismic data with towed streamers, such as near the shoreline, marshes and lagoons. In some cases, source explosives can be rammed into the unconsolidated sediments of transition zone environments rather than drilling more costly shot holes. Likewise, hydrophones can be placed by ramming to couple the receiver to the Earth better and to save time and money during survey acquisition.

See: acquisition,  coupling

2. n. [Formation Evaluation]

With reference to invasion, the volume between the flushed zone and the undisturbed zone in which the mud filtrate has only partially displaced the moveable formation fluids. One common model of invasion assumes a smooth transition in resistivity and other formation properties from the flushed to the undisturbed zone. Based on this assumption, the inner and outer diameters of invasion can be determined from array resistivity logs. Another common invasion model, which does not assume a smooth transition, is the annulus.

See: step profile