A modified pressure-pulse decay method for determining permeabilities of tight reservoir cores

• Modified pressure-pulse decay method is proposed to measure permeability of tight cores.
• The general solution for the method has been obtained.
• The accuracy of the method is much higher than the traditional pressure-pulse decay method.

Permeability is one of the most important parameters for characterizing fluid flow and production from reservoirs. In this paper, a modified pressure-pulse decay (PPD) method is proposed and tested for permeability measurement of tight cores. For this modified method, only one gas chamber is applied at one end of the test core sample, while the other end of the core is sealed. A small pressure pulse is applied to the gas chamber, and the pressure change in it is monitored with time. The mathematical model based on the experimental design has been built, and a general solution has been obtained by considering gas diffusion from the gas chamber to the core, under the pressure difference. Early-time and late-time solutions for the model are also presented for convenient application for post processing of experimental data. Simultaneously, experiments based on the modified model and on the traditional PPD model are carefully conducted to compare their results. The measured permeabilities of a core plug under different fluid pressure conditions, using the modified method, are in good agreement with those from the traditional PPD method. The advantages of the modified PPD method mainly lie in two points: one is that the results are much more accurate than that from the traditional PPD method when error exists in the measurement of chamber volume or pore volume. This advantage is especially significant for tight cores because their pore volume is usually hard to measure accurately. The other is that this modified method needs less transducers, a simpler experimental apparatus and easier operation.