Discussion/Reply: Advances in Measuring Permeability Address Shortcomings of Crushed-Rock Technique
- Dou Hong'en (Research Institute of Petroleum Exploration and Development, PetroChina)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- October 2012
- Document Type
- Journal Paper
- 160 - 164
- 2012. Copyright is retained by the author. This document is distributed by SPE with the permission of the author. Contact the author for permission to use material from this document.
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Dou Hong’en, SPE, Research Institute of Petroleum Exploration and Development, PetroChina
I was very glad to read paper SPE 152257, titled “Advances in Measuring Standards and Flow Properties Measurements for Tight Rocks Such as Shales,” summarized in the JPT August 2012 issue (p 57). I have several issues regarding the paper.
Sinha et al. mentioned that Darcy’s law may not be valid under those conditions that are at the pore pressure, the flow of gas through tight-rock samples such as shales may be in the free- molecular-flow regime or transition regime because of the relatively small pore sizes in nanometer range in this paper. However, they did not present any new method dealing with non-Darcy flow. In contrast, the authors used the Hagen-Poiseuille equation combined with Darcy’s law to obtain effective permeability. As it is well known, the Hagen-Poiseuille equation can only be used to describe the linear flow in accordance with Darcy’s law. Therefore, I do not think that the authors solve the non-Darcy flow of the permeability measurement at low-rate flow. Assuming that the fluid flow does not follow Darcy’s law in low permeability reservoirs, permeability value will not be obtained by Darcy’s law, in this case, if gas flow is high-rate at turbulent flow, the Forchheimer’s equation may be met, if gas/oil flow is low-rate/ultra-low-rate, the permeability is not a constant, and it will change with pressure gradient, for the above two cases, the permeability is difficult to measurement under laboratory conditions. Generally, low-rate and ultra-low-rate flow occurs in the tight rock of low-permeability reservoirs. Thus, the Forchheimer’s equation will not be considered applicable with the experimental data. Obviously, the authors will not derive the function relationship between the permeability and pressure gradient; and they cannot solve non-Darcy flow at low-rate flow in the low-permeability reservoirs. Once the study on the fluid flow in porous media is not based on Darcy’s law, any one permeability value will not be obtained in the whole process of cores displacement.
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