Estimating the surface relaxivity as a function of pore size from NMR T2 distributions and micro-tomographic images. (September 2017)

• Record Type: Journal Article
• Authors: Benavides, Francisco; Leiderman, Ricardo; Souza, Andre; Carneiro, Giovanna; Bagueira, Rodrigo
• Is Part Of: Computers & geosciences. Volume 106(2017)
• Page Start: 200
• Page End: 208
• Publication Date: 2017-09
• Subjects: Surface relaxivity -- NMR magnetization decay -- Digital petrophysics -- Random walk -- Pore size distribution; Environmental policy -- Periodicals; 550.5
• DOI: 10.1016/j.cageo.2017.06.016
• Languages: English
• ISSNs: 0098-3004

Abstract

Abstract: In the present work, we formulate and solve an inverse problem to recover the surface relaxivity as a function of pore size. The input data for our technique are the T 2 distribution measurement and the micro-tomographic image of the rock sample under investigation. We simulate the NMR relaxation signal for a given surface relaxivity function using the random walk method and rank different surface relaxivity functions according to the correlation of the resulting simulated T 2 distributions with the measured T 2 distribution. The optimization is performed using genetic algorithms and determines the surface relaxivity function whose corresponding simulated T 2 distribution best matches the measured T 2 distribution. In the proposed methodology, pore size is associated with a number of collisions in the random walk simulations. We illustrate the application of the proposed method by performing inversions from synthetic and laboratory input data and compare the obtained results with those obtained using the uniform relaxivity assumption. Highlights: We recover the surface relaxivity as function of pore size. The input data are T 2 distribution measurement and micro-tomographic image. We find the surface relaxivity that leads to the best T 2 distribution correlation. We show inversions from synthetic and laboratory input data. We compare the obtained results with those obtained with uniform relaxivity.