Reservoir EngineeringPVT and Rock-Fluid Properties

Effective Compressibility in Undersaturated Oil Reservoirs – Hawkins Formula

c_e = \frac{S_{oi} \cdot c_o + S_{wi} \cdot c_w + c_f}{1 - S_{wi}}

Effective Compressibility in Undersaturated Oil Reservoirs – Hawkins calculates effective compressibility for pvt and rock-fluid properties workflows in reservoir engineering.

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How engineers use this formula

Use this formula when the listed inputs (S_oi, c_o, S_wi, c_w, c_f) are known and the assumptions behind the cited pvt and rock-fluid properties relationship match the engineering case being checked.

Assumptions

Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
The declared units match the field-unit constants used in the formula.
The cited formula applies to the selected petroleum engineering workflow.

Limitations

The calculation does not replace a full engineering model or operating procedure.
Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.

Common mistakes

Mixing unit systems without converting the inputs.
Using default example values as field recommendations.
Applying the formula outside the source assumptions.

Default example

Using the default inputs, c_e equals 0.00002 1/psi.

S_oifraction

0.75

c_o1/psi

1.2e-5

S_wifraction

0.25

c_w1/psi

3e-6

c_f1/psi

5e-6

Inputs

S_oi

fraction

Initial Oil Saturation

c_o

1/psi

Oil Compressibility

S_wi

fraction

Initial Water Saturation

c_w

1/psi

Water Compressibility

c_f

1/psi

Formation Compressibility

Outputs

c_e

1/psi

Effective Compressibility

S_oi

fraction

Initial Oil Saturation (rearranged)

c_o

1/psi

Oil Compressibility (rearranged)

S_wi

fraction

Initial Water Saturation (rearranged)

c_w

1/psi

Water Compressibility (rearranged)

c_f

1/psi

Formation Compressibility (rearranged)

Source and review

reviewed

Hawkins, M.F. (1956). Fluid Flow Through Porous Media. University of Tulsa Petroleum Abstracts, Page: 8.; Ahmed, T., McKinney, P.D. 2005. Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter: 5, Page: 334.

Source