Skin-effect (from English skin) in oil-and-gas sphere – means phenomena of additional resistivity arising in bottom-hole formation zone and in face area to fluid influx into the well.

Skin-effect results from production-induced impact on the bottom-hole formation zone when completing the well. Due to that, gas-dynamic features of the bottom-hole zone differ from the other part of the pay zone.

Skin-effect provides quantitative characteristic of the difference between equivalent permeability of the bottom-hole zone of the well from the other part of the drainage area. It reflects the quality of completion job dependent on the following factors: degree of reservoir contamination with drilling mud and flushing sludge; nature and quality of reservoir connection with the wellbore; type and efficiency of fluid influx into the well (enhanced oil recovery), etc.

The numerical value is defined by gas-dynamic methods of well survey as an outcome of processing the bottom-hole build-up and stabilization curves.

Positive skin-effect values (above zero) indicate poor quality of completion. Negative skin-effect values (below zero) normally are associated with production-induced generation of caverns, fissures and channels in the bottom-hole zone.