In a high-pressure region gas flow rate for a petroleum reservoir, "skin" (See Skin Factor) refers to a concept in petroleum engineering that accounts for the additional resistance (or sometimes enhancement) to gas flow near the wellbore. It’s a dimensionless number that tweaks the flow rate calculation to reflect real-world conditions around the well that aren’t captured by basic rock and pressure assumptions.
When gas flows from a high-pressure region in the reservoir toward the well, it doesn’t always move smoothly. The area right around the wellbore, called the near-wellbore zone, can get messed up during drilling, completion, or production. Maybe the drilling mud clogged the pores, or perforations didn’t punch through right, or even scale built up over time. This extra resistance reduces the flow rate compared to what you’d expect from a perfect, clean reservoir. On the flip side, if the well’s been stimulated, like with acidizing or fracturing, it might flow better than expected. "Skin" captures all that.
