A Note on the Skin Effect

Abstract

Horner' and van Everdingen' have shown that the pressure drop within the wellbore, as a result of having produced the well at a constant rate q for time {, where t is sufficiently large, is:.6.pe = 47rk e h In /Lefr:van Everdingen observed that better agreement between theory and well performance can be obtained if, instead of assuming the permeability is ke everywhere about the well, it is assumed the permeability near the wellbore is substantially reduced as a result of drilling, completion andlor production practices. In order to account for the additional pressure drop he introduced the dimensionless quantity S, the skin effect factor, so that Eq. 1 becomes:.6.p, = 4::eh [ In ( /L~;~: ) + .809 + 2 s] .(2)Eq. 2 might have also been obtained as follows. Assume a zone of altered permeability k. exists about the well out to a radius r,,, and beyond that the unaltered, external permeability k e • The additional pressure drop required to overcome this skin of reduced permeability may be calculated with sufficient accuracy using the incompressible flow equation; for Brownscombe and Collins' have shown almost no difference between compressible and incompressible steady-state flow, in the vicinity of the wellbore, and the small volume of fluid in the vicinity of the wellbore makes unsteady-state mechanics unnecessary. Then, q/Lln(r.lrw) q0

Rate transient analysis of Well-07 and Well-10 of Habiganj gas field, Bangladesh

“…Additionally, the dimensionless value of skin factor (s) was estimated surrounding the Well-07 and Well-10 to 7.017 and 7.014, respectively. So, permeability near these two wellbore regions was substantially reduced as a result of the highly valued skin effect as recommended by Hawkins Jr. (1956). This reduced permeability causes an additional pressure drop across the altered zone.…”

“…In this model, the altered zone around the wellbore is assumed to have uniform permeability k s out to a radius r s , beyond which the formation permeability, k, is unaltered (Altered zone and skin effect 2016). Everdingen found that better agreement between theory and well performance is possible, if the permeability reduction near the wellbore region is assumed due to drilling, completion and production practices (Hawkins Jr. 1956). …”

Derivation and application of mathematical model for well test analysis with variable skin factor in hydrocarbon reservoirs

“…In light of the definition of the skin factor in steady radial fluid flow of vertical wells, the mathematical equation is given as 4,22 …”

“…Hawkins introduced an improved model called "thick-skin mathematical model" which was accepted by researchers and engineers and developed further into what is now called "skin factor". [2][3][4] There are many factors that causes skin effect which includes invasion of mud during drilling process, incomplete perforation, fines migration, hydraulic fracturing, acidification and so on. [5][6][7][8] Skin factor is an important parameter that is obtained in well test analysis.…”

Hydrogeologic characterization of a fractured granitic rock aquifer, Raymond, California

“…Assuming that the zone of differing permeability is an annular region around the wellbore, Hawkins (1956) showed that (4.8)…”