2019 AAPG Annual Convention and Exhibition:

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Quantifying the Influence of Fractures for More Accurate Laboratory Measurement of Shale Matrix Permeability


Quantifying the Influence of Fractures for More Accurate Laboratory Measurement of Shale Matrix Permeability

Sheng Peng*1, Bo Ren2, Mianmo Meng3, 1

1. Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, Texas 78713, USA

2. Hildebrand Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, TX 78703, USA

3. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China

Abstract: Matrix permeability is a key petrophysical parameter in reservoir evaluation and simulation. However, measurement of this parameter still remains problematic for unconventional reservoirs. One of the biggest challenges lies in the influence of fractures, which can be artificially induced and are ubiquitous in almost all shale plug samples. Inclusion of fractures in measurement and data interpretation can lead to overestimation of shale-matrix permeability. In this study, new experimental and data analysis procedures are developed for more accurate measurement of shale matrix permeability based on a previous work (Peng and Loucks, 2016). The new experimental procedures also allow fast pressure equilibrium and takes 15-60 minutes, which is less time than that compared to other methods such as pulse-decay or steady-state methods. Permeability and porosity values under confining pressure are obtained from quantitative analysis on measured pressure-decay curve for oven-dried samples. The influence of fractures on matrix porosity and permeability is quantified and excluded. Reliability and consistency of the measurement results are confirmed through multiple means, including analytical solution back-calculation, numerical modeling, and multiple measurements for similar samples but with different plug diameters. Because the influence of fractures is explicitly excluded in the data analysis, the new method is also more flexible regarding sample conditions – even broken plug samples with fractures can be used in this method. This is another advantage of the new method given the difficulty in obtaining “intact” plugs because of the fissility of shale. The newly-developed method can thus serve as a fast yet reliable technique for “real” shale matrix permeability measurement. Measurement results for 50+ shale samples with detailed lithofacies information will be presented.