Wellbore Skin and Formation Damage

Introduction

Skin is method for quantifying damage to operating wells represents the wellbore condition by an incremental pressure drop at the wellbore in addition to the normal pressure profile due to flow in the formation. In other words, the ideal scenario versus actual productivity.

The superposed pressure drop called the skin effect is often presumed to occur over an infinitesimally thin skin zone in which the permeability impairment is confined.

However, skin can also be considered to a finite region region around the wellbore. The skin factor s are is positive for localized permeability reduction in the neighbourhood of a producing well. However, in this region, it is also possible to achieve an increase in permeability (or effective permeability) relative to the value in the remainder of the formation as a result of well stimulation treatments such as acidizing or fracturing.

The image below shows:

For positive skin, the pressure drop at the wellbore is greater for a given flow rate
For a negative skin, the pressure drop at the wellbore is reduced for a given flow rate
Zero skin = is the ideal/normal scenario.

Associated Pressure Drop

The pressure and/or dimensionless pressure drop associated with a skin can be calculated from:

Where skin = dP_D

Nomenclatures (Field Units)

k = Permeability, md

h = Net pay, ft

B = Oil Formation Volume factor (dimensionless)

u = Oil Viscosity (cp)

References:

Gas Research Institute, A Guide to Coalbed Methane Reservoir Engineering, 1996
T. A. Blasingame, Analysis Well Performance, v20230723, Texas A&M

Introduction

Associated Pressure Drop

Nomenclatures (Field Units)

See Also:

Related CSG Reading:

References: