Renjing Liu, SPE, Huiqing Liu, Xiusheng Li, Jing Wang, China University of
Petroleum (Beijing); and Changting Pang, China Oilfield Service Ltd., CNOOC
As an important parameter of multiphase flow in porous media, relative
permeability curve is often calculated by JBN method which ignores the
capillary pressure. However, owing to the fine throat and the complex construct
in extra low permeability reservoir, the capillary pressure is very
significant. In addition, researches have shown that the flow in low
permeability media doesn’t follow the Darcy’s law and there is threshold
pressure gradient occurring in the percolation. Therefore, the traditional
method is no longer available for the extra low permeability reservoirs and a
new method is needed urgently to resolve this problem.
In this paper, the relative permeability of extra-low permeability core was
calculated by three methods: JBN method, fractal model and modified JBN method.
The fractal model was set up based on the capillary pressure curve and the
fractal geometry theory. The modified JBN method taken into the effects of
capillary pressure and threshold pressure gradient, and a semi-log fit function
other than polynomial function was used to improve the accuracy.
The results show that, comparing with JBN method, the fractal model and the
modified JBN method can predict the relative permeability more accurately. And
the modified JBN method is the best. The water cut calculated by the new method
matched the production data better than that calculated by JBN method.
The new method overcomes the limitations of previous researches. It can be used
to calculate relative permeability for extra low permeability reservoirs more
accurately and help to develop extra low permeability reservoirs more
Relative permeability is an important parameter of multiphase flow in porous
media, which is the required parameter for the plan of oilfield development,
dynamic prediction and numerical simulation. The relative permeability curve
can predict oil production rate, ultimate recovery and water cut. At present,
the measure methods of relative permeability are usually the followings: steady
method; unsteady method; capillary pressure method; centrifugal method and
production data method (Firoozabadi, A., Aziz, K. 1988, Li Kewen et al. 1989,
E.Ebeltoft et al. 1998, C. Wouter Botermans et al. 2001, Janos Toth et al.
2002). The fore two methods are usually used in laboratory researches.
In steady method, the fluid was injected as a fixed ratio until the equilibrium
state of saturation and pressure was established. The key focus in this
experiment is to remove or reduce the saturation gradient caused by the
capillary pressure effect. There are several methods: Penn. State method,
single core method, immobilizing fluid method, Hassler method, Hafford method
and disperse injection method. Steady method is the most direct method and is
the most easy to explain method. But it is difficult to get the relative
permeability curve with continuous saturation distribution and it is only to
get one point one time. Therefore, it is very time-consuming. In addition, the
development effect predicted by the data gotten from steady method may cause
very much error because the saturation gradient is changing continuously during
Unsteady method is that the core was saturated by one fluid and then it is
displaced by another fluid. Welge, Efros, Johnson, Jones develop and improve
this method, and the JBN method was created, which is extend to three-phase
relative permeability calculation.