Mohammed A. Aqel

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ORIGINAL PAPERRESEARCH NOTE: permeability control on the relationshipbetween nuclear magnetic resonance (NMR) measured porosityand routine core porosityMohammed A. Aqel1Received: 6 January 2015 /Accepted: 20 January 2016 /Published online: 21 April 2016# The Author(s) 2016. This article is published with open access at Springerlink.comAbstract A new criterium is proposed as a hypothesisthat gives a dividing line between conventional and un-conventional reservoir rocks from the permeability pointof view. For rocks with higher permeability, the labora-tory porosity values are higher than the NMR porosities.For rocks of lower permeability, the laboratory porosityvalues are lower compared to NMR porosities. Thistendency of permeability to control the relation betweenporosities measured by two techniques is noticed inpublished data collected from different literaturesources.Keywords Unconventional reservoir rocks . Permeability .NMR porosity . Routine porosityIntroductionNMR and laboratory porosity measurements were collectedfrom published papers for carbonate rock plugs. Three sets ofdata were used in this study, two of which are from the samesource: (1) Twenty-seven (27) carbonate core plugs analyzed bylow-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 carbonatesin West Texas): Field A. (Lyne et al. 1996), and (3) a total of29 core plugs selected from off-shore, carbonate, oil-producingformations (the Clearfork carbonates in West Texas): Field N.(Lyne et al. 1996).Porosity and permeability proceduresPorosity can be determined by different lab procedures.Porosity is determined by using helium-gas expansion as de-scribed by Boyle’s law (Kazimierz et al, 2004) where in agaseous system at a given temperature, the product of absolutepressure and volume is constant. Also, porosity is calculatedby using saturation method where the pore volume is deter-mined by dividing the difference in weight between the satu-rated sample and the dry sample by the known density of thesaturating fluid.And by applying Archie’s laws on laboratory-measuredelectrical properties (i.e., resistivity, formation resistivity fac-tor, and cementation exponent), porosity is calculated (Efniket al, 2006). In NMR measurements, core plug measurementsprovide important details about the variations in the pore size,and free/bound fluid volumes (Moss, 2004).Using Darcy’s law, permeability is calculated from fluidflow rate, cross-sectional area of the core sample, differentialpressure (between upstream and downstream pressures), vis-cosity of flowing fluid, and length of the core sample.For the first set (Chang et al, 1997), plugs were cleaned forlaboratory porosity measurements by hydrostatic weighing intoluene and for Klinkenberg-corrected air permeability mea-surements. Then, the samples were saturated by brine forNMR porosity measurements. Similarly, the second set ofplugs (Lyne et al, 1996) were cleaned and resaturated withbrine. Laboratory (conventional) porosity and permeabilitymeasurements were conducted by following the Archimedesprinciple and the Klinkenberg correction, respectively(Tanikawa and Shimamoto, 2006). The NMR porosity values* Mohammed A. Aqelaqeel15@hotmail.com1 King Fahd University of Petroleum & Minerals, Dhahran, SaudiArabiaArab J Geosci (2016) 9: 350DOI 10.1007/s12517-016-2335-8Fig. 1 Tendency of permeabilitycontrol on porosities’ relationshipfor 75 % of the data: Permeabilityversus relative error betweenNMR and Lab porosities (Datataken from Chang et al. 1997)Fig. 2 Tendency of permeabilitycontrol on porosities’ relationshipfor 74 % of the data for Field A:Permeability versus relative errorbetween NMR and Lab porosities(Data taken from Lyne et al.1996). Note that this group can bedivided into two sets (red squareswith higher permeability valuesand blue diamonds with lowerpermeability values) having thesame relationshipFig. 3 Tendency of permeabilitycontrol on porosities’ relationshipfor 100 % of the data for Field N:Permeability versus relative errorbetween NMR and Lab porosities350 Page 2 of 3 Arab J Geosci (2016) 9: 350were calculated directly from the NMR signals as they areproportional to the volume of fluids in the pore systems.InterpretationInverse relations between the relative errors of porosities andpermeability values are shown in Figs. 1, 2, and 3. WhenNMR porosity is greater than conventional plug porosity, thepermeability value is expected to be low and vice versa.HypothesisThe measured permeability values were plotted against therelative error between “NMR” porosity and “LAB” porosity(Figs. 1–3).The permeability controls the relation between NMR-measured porosity and conventional laboratory-measured po-rosity according to the best fit relationship:y ¼ a ebxwhere y is the permeability and x is the relative error of po-rosity measurements.I assume, as a work hypothesis, that for higher perme-ability values, the laboratory porosity values are higherthan the NMR porosities (Fig. 4). And, for lower valuesof permeability, the laboratory porosity values are lowercompared to NMR porosities. It seems likely that thisobservation would establish a discriminatory threshold be-tween conventional and tight rocks. Further research isneeded to involve in this study the three classic log-derived (density, neutron, and sonic) porosities and theirrelation with the NMR porosity.ConclusionReferencesChang D, Vinega H, Morriss C, Straley C (1997) Effective porosity,producible fluid, and permeability in carbonates from NMRLogging. The Log Analyst, March.-April, 60–72Efnik M, Dernaika M, Kalam M (2006) Evaluation of Water Saturationfrom Laboratory to Logs. The International Symposium of theSociety of Core Analysts. SCA2006-56 p 1–6Kazimierz T, Jacek T, Stanisław R (2004) Evaluation of Rock PorosityMeasurement Accuracy with a Helium Porosimeter. Acta MontanSlovaca 9(3), p 316–318Lyne A, Vaflni G, Ghilardotti G (1996) Determination of petrophysicalproperties of carbonate rocks by NMR relaxometry. Society ofPetroleum Engineers, (SPE 36852), 331–339Moss A (2004) NMR Core Plug Measurements to Compliment SCALstudies. The International Symposium of the Society of CoreAnalysts. SCA2004-47 p 1–6Tanikawa W, Shimamoto T (2006) Klinkenberg effect for gas permeabil-ity and its comparison to water permeability for porous sedimentaryrocks. Hydrol Earth Syst Sci Discuss 3, 1315–1338Fig. 4 All data points plotted inone graph showing the tendencyArab J Geosci (2016) 9: 350 Page 3 of 3 350The proposed trend—if verified—could delineate the bound-ary between conventional and unconventional rocks from thepermeability point of view. However, more data are neededfor a better definition of the control parameters.Acknowledgments The author thanks Professor Gabor Korvin (KingFahd University of Petroleum and Minerals, KFUPM, Saudi Arabia) forhis valuable comments and suggestions which improved the originalmanuscript.Open Access This article is distributed under the terms of the CreativeCommons Attr ibution 4.0 International License (http: / /creativecommons.org/licenses/by/4.0/), which permits unrestricteduse, distribution, and reproduction in any medium, provided you giveappropriate credit to the original author(s) and the source, provide a linkto the Creative Commons license, and indicate if changes were made.

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RESEARCH NOTE: permeability control on the relationship between nuclear magnetic resonance (NMR) measured porosity and routine core porosity

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RESEARCH NOTE: permeability control on the relationship between nuclear magnetic resonance (NMR) measured porosity and routine core porosity

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