In the ever-evolving landscape of energy exploration, precision in measuring the properties of subsurface rocks is paramount. A recent study published in the journal “Bulletin of the Tomsk Polytechnic University: Engineering of Georesources” sheds new light on the intricacies of nuclear magnetic resonance (NMR) relaxometry, a method increasingly used in well logging and laboratory investigations. The research, led by Timofey A. Yanushenko, delves into the nuances of how grain size can affect the accuracy of porosity measurements, offering insights that could revolutionize how the energy sector approaches reservoir characterization.
NMR relaxometry is a cutting-edge technique used to determine petrophysical properties such as porosity, permeability, and fluid saturation. However, the method’s reliability has been called into question due to its reliance on a simplified model of pore space as a set of spheres of various diameters. This model, while useful, does not always align with the complex structures found in granular rocks.
Yanushenko’s study aims to bridge this gap by examining the influence of grain size on NMR relaxometry measurements. Using artificial samples made from various sand and quartz glass bead fractions, the research team employed water-saturation, gas-volumetric, and NMR relaxometry methods to determine porosity. The results were striking. For samples with grain sizes less than 0.160 mm, NMR relaxometry consistently underestimated porosity, regardless of whether the samples were consolidated or unconsolidated.
“The effect of underestimated porosity was observed across all our samples with smaller grain sizes,” Yanushenko noted. “This suggests that the complex shape and increased specific surface area of the samples, which grow as particle size decreases, play a significant role in this discrepancy.”
To rule out other potential factors, the team conducted a thorough analysis of the sand composition using X-ray diffraction and assessed particle shape and size through polished specimens. The findings confirmed that these factors were not the primary cause of the underestimated porosity effect. Further validation with additional statistical samples and different NMR relaxometers reinforced the reproducibility of the results.
The implications of this research are profound for the energy sector. Accurate porosity measurements are crucial for assessing the potential of oil and gas reservoirs. An underestimation of porosity can lead to misjudgments in resource estimation, affecting investment decisions and operational strategies. By understanding the limitations of NMR relaxometry in fine-grained samples, energy companies can adopt more precise measurement techniques or adjust their interpretations accordingly.
“This study highlights the need for a more nuanced approach to porosity measurement in fine-grained rocks,” Yanushenko explained. “As we push the boundaries of exploration into more complex reservoirs, it’s essential to refine our tools and methods to ensure accurate and reliable data.”
The research published in the Bulletin of the Tomsk Polytechnic University: Engineering of Georesources, offers a glimpse into the future of reservoir characterization. As the energy sector continues to evolve, the insights gained from this study could pave the way for more accurate and efficient exploration and production techniques. By addressing the challenges posed by fine-grained samples, the industry can move closer to unlocking the full potential of subsurface resources, ensuring a more sustainable and profitable future.