Enter the permeability, viscosity, thickness, and pressure drop into the calculator to determine the Forster Radius. This calculator helps in evaluating the effective radius of a wellbore during a pressure transient test.

Forster Radius Formula

The following formula is used to calculate the Forster Radius. 

FR = √((162.6 * k * h) / (μ * ΔP))

Variables:

  • FR is the Forster Radius (feet)
  • k is the permeability of the formation (millidarcies)
  • h is the thickness of the formation (feet)
  • μ is the viscosity of the fluid (centipoise)
  • ΔP is the pressure drop across the formation (psi)

To calculate the Forster Radius, take the square root of the product of 162.6 times the permeability and thickness of the formation, divided by the product of the viscosity and pressure drop.

What is a Forster Radius?

The Forster Radius is a concept used in petroleum engineering to describe the effective wellbore radius during a pressure transient test. It is a measure of the distance from the wellbore to the point in the reservoir where the pressure has dropped to half the value of the pressure drop at the wellbore. This radius is important for understanding the flow characteristics and the extent of the reservoir influenced by the well during the test.

How to Calculate Forster Radius?

The following steps outline how to calculate the Forster Radius.

  1. First, determine the permeability of the formation (k) in millidarcies.
  2. Next, determine the viscosity of the fluid (μ) in centipoise.
  3. Next, determine the thickness of the formation (h) in feet.
  4. Next, determine the pressure drop across the formation (ΔP) in psi.
  5. Next, gather the formula from above = FR = √((162.6 * k * h) / (μ * ΔP)).
  6. Finally, calculate the Forster Radius (FR) in feet.
  7. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Permeability of the formation (k) = 150 millidarcies

Viscosity of the fluid (μ) = 1 centipoise

Thickness of the formation (h) = 50 feet

Pressure drop across the formation (ΔP) = 200 psi