## How to Calculate and Solve for Diffusivity Constant | Well Testing

The image above represents diffusivity constant.

To compute for the diffusivity constant, four essential parameters are needed and these parameters are pemerability (k), porosity (φ), viscosity (μ) and total compressibility (CT).

The formula for calculating diffusivity constant:

η = 0.000263k / φμCT

Where;

η = Diffusivity Constant
k = Permeability
φ = Porosity
μ = Viscosity
CT = Total Compressibility

Let’s solve an example;
Find the diffusivity constant where the permeability is 12, porosity is 9, viscosity is 7 and total compressibility is 11.

This implies that;

k = Permeability = 12
φ = Porosity = 9
μ = Viscosity = 7
CT = Total Compressibility = 11

η = 0.000263k /  φμCT
η = 0.000263 x 12 / 9 x 7 x 11
η = 0.003156 / 693
η = 0.000004554112554112554

Therefore, the diffusivity constant is 0.000004554112554112554.

Calculating the Permeability when the Diffusivity Constant, Porosity, Viscosity and Total Compressibility is Given.

k = n x φμCT / 0.000263

Where;

k = Permeability
η = Diffusivity Constant
φ = Porosity
μ = Viscosity
CT = Total Compressibility

Let’s solve an example;
Find the permeability where the diffusivity constant is 24, porosity is 10, viscosity is 5 and total compressibility is 13.

This implies that;

η = Diffusivity Constant = 24
φ = Porosity = 10
μ = Viscosity = 5
CT = Total Compressibility = 13

k = n x φμCT / 0.000263
k = 24 x 10 x 5 x 13 / 0.000263
k = 15600 / 0.000263
k = 59315589.3536

Therefore, the permeability is 59315589.3536.

Calculating the Porosity when the Diffusivity Constant, Permeability, Viscosity and Total Compressibility is Given.

φ = 0.000263k / nμCT

Where;

φ = Porosity
k = Permeability
η = Diffusivity Constant
μ = Viscosity
CT = Total Compressibility

Let’s solve an example;
Find the porosity where the diffusivity constant is 28, permeability is 8, viscosity is 12 and total compressibility is 18.

This implies that;

k = Permeability = 8
η = Diffusivity Constant = 28
μ = Viscosity = 12
CT = Total Compressibility = 18

φ = 0.000263k / nμCT
φ = 0.000263 x 8 / 28 x 12 x 18
φ = 0.002104 / 6048
φ = 3.478e-7

Therefore, the porosity is 3.47e-7.