Advances in Measuring Permeability Address Shortcomings of Crushed-Rock Technique
- Adam Wilson (JPT Editorial Manager)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- August 2012
- Document Type
- Journal Paper
- 57 - 61
- 2012. Society of Petroleum Engineers
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- 217 since 2007
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This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 152257, "Advances in Measurement Standards and Flow Properties Measurements for Tight Rocks Such as Shales," S. Sinha, SPE, E.M. Braun, SPE, Q.R. Passey, SPE, S.A. Leonardi, SPE, A.C. Wood III, T. Zirkle, SPE, J.A. Boros, SPE, and R.A. Kudva, SPE, ExxonMobil Upstream Research, prepared for the 2012 SPE/EAGE European Unconventional Resources Conference and Exhibition, Vienna, Austria, 20-22 March. The paper has not been peer reviewed.
The most commonly used industry method for measuring permeability is the Gas Research Institute (GRI) technique or its variants, which involve the use of crushed samples. The accuracy of such techniques, however, is questionable because of a number of inadequacies, such as the absence of reservoir overburden stress while conducting these measurements. In addition to the questionable accuracy of crushed-rock techniques, studies have indicated that there is significant variability in results reported by different laboratories that use crushed-rock techniques to measure permeability on shale samples. The complete paper presents a robust steady-state technique for measuring permeability on intact tight-rock samples under reservoir overburden stress. These standards can be used to calibrate any permeability-measurement apparatus used on intact tight-rock samples, such as shales, to enable delivery of consistent results across different laboratories.
For low-permeability reservoirs such as shales, the GRI method is popular because of the relatively quick times associated with the measurements as a result of the increased surface area available and because of the perception that measurements on intact low-permeability plug samples by use of well-established methods such as steady state or pulse decay could take such long times that it would make such measurements impractical. However, using crushed rock for measuring permeability has a number of inadequacies, resulting in skepticism associated with the accuracy of such measurements. Perhaps the most serious drawback of the crushed-rock method for measuring permeability, as presented in a number of studies, is the wide variability in results reported by different vendors, with results that could differ by as much as three orders of magnitude.
Shortcomings of GRI Technique of Measuring Permeability
The GRI, or crushed-rock, technique for measuring permeability is a relatively fast method for measuring permeability on low-permeability samples, but it has the following shortcomings.
Absence of Overburden Stress. The GRI technique is implemented on crushed rock samples, and, therefore, these measurements are not conducted at reservoir overburden stress. Ignoring the effect of overburden stress while measuring the permeability could lead to significant discrepancy between permeability measured in the laboratory and in-situ permeability.
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