Wellbore Radius & Equivalent Wellbore Radius

Introduction

In the AFA models, the wellbore is assumed to be cylindrical and has a specific radius called wellbore radius. The wellbore radius is used to determine the sandface area (2 rw h) which represents the area through which all the produced reservoir fluids must flow. This area has a significant effect on the flowing wellbore pressure.

In real life, the area of contact between the wellbore and the formation is rarely cylindrical due to perforations, scale and/or wax deposition, and so on.

Equivalent Wellbore Radius

For some purposes, it may be more convenient to take non-ideal conditions into account by the concept of equivalent wellbore radius. In this scenario, we attempt to model a fracture or stimulated region as a skin. A fictitious well with a larger radius is intended capture the effect of deeper penetration into the reservoir, or the altered permeability region.

The simple relationship is:

Equivalent Xf

Alternatively, the apparent or effective wellbore radius can be defined as:

References

• Jelmert, Tom Aage, Introductory Well Testing , 2013

• Fikri J. Kuchuk, T. S. Ramakrishnan, Mustafa Onur, Wireline Formation Testing: Hardware, Pressure Transient Testing, Interpretation and Sampling , 2021, Society of Petroleum Engineers