RESEARCH NOTE: permeability control on the relationship between nuclear magnetic resonance (NMR) measured porosity and r
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ORIGINAL PAPER
RESEARCH NOTE: permeability control on the relationship between nuclear magnetic resonance (NMR) measured porosity and routine core porosity Mohammed A. Aqel 1
Received: 6 January 2015 / Accepted: 20 January 2016 # The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract A new criterium is proposed as a hypothesis that gives a dividing line between conventional and unconventional reservoir rocks from the permeability point of view. For rocks with higher permeability, the laboratory porosity values are higher than the NMR porosities. For rocks of lower permeability, the laboratory porosity values are lower compared to NMR porosities. This tendency of permeability to control the relation between porosities measured by two techniques is noticed in published data collected from different literature sources. Keywords Unconventional reservoir rocks . Permeability . NMR porosity . Routine porosity
Introduction NMR and laboratory porosity measurements were collected from published papers for carbonate rock plugs. Three sets of data were used in this study, two of which are from the same source: (1) Twenty-seven (27) carbonate core plugs analyzed by low-field NMR and conventional core analysis (Chang et al. 1997), (2) a total of 35 core plugs selected from off-shore, carbonate, oil-producing formations (the Glorieta carbonates in West Texas): Field A. (Lyne et al. 1996), and (3) a total of 29 core plugs selected from off-shore, carbonate, oil-producing * Mohammed A. Aqel [email protected]
1
King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia
formations (the Clearfork carbonates in West Texas): Field N. (Lyne et al. 1996).
Porosity and permeability procedures Porosity can be determined by different lab procedures. Porosity is determined by using helium-gas expansion as described by Boyle’s law (Kazimierz et al, 2004) where in a gaseous system at a given temperature, the product of absolute pressure and volume is constant. Also, porosity is calculated by using saturation method where the pore volume is determined by dividing the difference in weight between the saturated sample and the dry sample by the known density of the saturating fluid. And by applying Archie’s laws on laboratory-measured electrical properties (i.e., resistivity, formation resistivity factor, and cementation exponent), porosity is calculated (Efnik et al, 2006). In NMR measurements, core plug measurements provide important details about the variations in the pore size, and free/bound fluid volumes (Moss, 2004). Using Darcy’s law, permeability is calculated from fluid flow rate, cross-sectional area of the core sample, differential pressure (between upstream and downstream pressures), viscosity of flowing fluid, and length of the core sample. For the first set (Chang et al, 1997), plugs were cleaned for laboratory porosity measurements by hydrostatic weighing in toluene and for Klinkenberg-corrected air permeability measurements. Then, the samples were saturated by brine for NMR p
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