Corey Relative Permeability Curves

Introduction

Burdine (1953) developed the following model to predict wetting and non-wetting phases relative permeabilities, this model was developed to be used in conventional reservoir where it was used just one parameter , that means pore size distribution index. In the original Burdine correlation, . Seidle (2011) shows that this model can be applied for non-conventional reservoir such as coal seam gas (coal bed methane) when is a variable.

The gas relative permeability is given by:

The water relative permeability is given by:

The normalized water saturation is given by:

where:

- gas relative permeability at irreducible water (also KrgMax);

- empirical coefficient;

- empirical coefficient;

- irreducible water saturation (also defined as connate water saturation);

- current water saturation.

Based on Burdine correlation, Corey et al. (1956) developed the following models for water-oil systems and an explicit correlation for gas-oil systems, which is often used for coal seam gas (coal bed methane) (Dandekar 2013). Note, a generalized form is shown:

where:

- gas relative permeability;

- gas relative permeability at irreducible water (also defined as );

- water relative permeability;

- water relative permeability at irreducible gas (also defined as );

- irreducible gas saturation (also defined as connate gas saturation);

- Corey coefficient for gas;

- Corey coefficient for gas;

Demonstration

The video below illustrates how the various inputs change the shape and behavoir of the Corey curves. In particular, the video demonstrates the impact of:

• Corey water exponent n_w

• Corey gas exponent n_g

• Maximum relative permeability to gas k_rg Max

• Maximum relative permeability to water k_rw Max

Final Comments

• No “best” model really exists. There have been many modifications to Corey Curves for.

• Curves can often be difficult to evaluate without substantial data.

References

• Baker, Richard O. / Yarranton, Harvey W. / Jensen, Jerry L. , Practical Reservoir Engineering and Characterization, 2015, Gulf Professional Publishing

• Seidle, John. Fundamentals of Coalbed Methane: Reservoir Engineering, 2011, PennWell Corporation.

• Dandekar, A.Y. Petroleum reservoir rock and fluid properties, 2013 CRC press.