New Insights into the Formation and Properties of Wellbore Skin: Why We Have to Rethink the Concept

The deposition of fine‐grained material of low permeability on the borehole wall during drilling (wellbore skin) is a common problem affecting the operation and efficiency of water wells. Here, we present new data and novel insights from four excavated dewatering wells from a lignite surface mine. All wells have the same age, are of similar construction, and were sampled at two different depths each. The thickness of the skin layer increases with depth. Its composition and permeability is strongly influenced by the surrounding aquifer material. Nonuniform sediments of low permeability result in less permeable wellbore skin deposits. The presence of discontinuities in the skin layer may be a determining feature for the resulting flow to wells, especially with skin layers of low permeability. The presence of naturally occurring swelling clay (smectite) provides the skin layer with a significant self‐sealing capacity. Article impact statement: In‐depth analysis of samples of wellbore skin, insights into formation, dependency on aquifer properties, and role of discontinuities.