Remerciez-le!

Remerciez @Admin pour avoir partagé cet document gratuitement, de la manière la plus simple, en partageant sur les réseaux sociaux.

See discussions, stats, and author profiles for this publication at: https://ww

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/269631174 Quantification of pore structure and its effect on sonic velocity and permeability in carbonates Article in AAPG Bulletin · October 2009 DOI: 10.1306/05270909001 CITATIONS 98 READS 345 5 authors, including: Some of the authors of this publication are also working on these related projects: The Tropical Ostracod Record of The Maldives and its Paleoceanographic Implications View project Maldives Monsoon, Sea Level and Currents View project Ralf J. Weger University of Miami 38 PUBLICATIONS 671 CITATIONS SEE PROFILE Gregor P. Eberli University of Miami 511 PUBLICATIONS 4,329 CITATIONS SEE PROFILE Gregor Baechle Repsol, Houston, USA 36 PUBLICATIONS 572 CITATIONS SEE PROFILE Jose Luis Massaferro YPF 25 PUBLICATIONS 275 CITATIONS SEE PROFILE All content following this page was uploaded by Gregor P. Eberli on 19 April 2016. The user has requested enhancement of the downloaded file. GEOHORIZONS Quantification of pore structure and its effect on sonic velocity and permeability in carbonates Ralf J. Weger, Gregor P. Eberli, Gregor T. Baechle, Jose L. Massaferro, and Yue-Feng Sun ABSTRACT Carbonate rocks commonly contain a variety of pore types that can vary in size over several orders of magnitude. Tradi- tional pore-type classifications describe these pore structures but are inadequate for correlations to the rock’s physical prop- erties. We introduce a digital image analysis (DIA) method that produces quantitative pore-space parameters, which can be linked to physical properties in carbonates, in particular sonic velocity and permeability. The DIA parameters, derived from thin sections, capture two-dimensional pore size (DomSize), roundness (g), aspect ratio (AR), and pore network complexity (PoA). Comparing these DIA parameters to porosity, permeability, and P-wave velocity shows that, in addition to porosity, the combined ef- fect of microporosity, the pore network complexity, and pore size of the macropores is most influential for the acoustic be- havior. Combining these parameters with porosity improves the coefficient of determination (R2) velocity estimates from 0.542 to 0.840. The analysis shows that samples with large sim- ple pores and a small amount of microporosity display higher acoustic velocity at a given porosity than samples with small, complicated pores. Estimates of permeability from porosity alone are very ineffective (R2 = 0.143) but can be improved when pore geometry information PoA (R2 = 0.415) and Dom- Size (R2 = 0.383) are incorporated. Furthermore, results from the correlation of DIA parameters to acoustic data reveal that (1) intergrain and/or intercrystalline AUTHORS Ralf J. Weger University of Miami, Rosenstiel School of Marine and Atmospheric Science, Division of Marine Geology and Geo- physics, 4600 Rickenbacker Causeway, Miami, Florida 33129; rweger@rsmas.miami.edu Ralf J. Weger was a postdoctoral researcher with the Comparative Sedimentology Laboratory at the University of Miami when the article was written. He received his B.S. degree in systems analysis (2000) and his Ph.D. in marine geology and geophysics (2006) from the University of Miami. His dissertation focuses on quantitative pore- and rock-type parameters in carbonates and their relationship to velocity deviations. His main interests range from processing and visu- alization of geophysical data to petrophysical characterization of carbonate rocks. Gregor P. Eberli University of Miami, Ro- senstiel School of Marine and Atmospheric Science, Division of Marine Geology and Geophys- ics, 4600 Rickenbacker Causeway, Miami, Florida 33129; geberli@rsmas.miami.edu Gregor P. Eberli is a professor in the Division of Marine Geology and Geophysics at the University of Miami and the Director of the Comparative Sedimentology Laboratory. He received his Ph.D. from the Swiss Institute of Technology (ETH) in Zürich, Switzerland. His research integrates the sedimentology, stratigraphy, and petrophysics of carbonates. With laboratory experiments and seismic modeling, his group tries to understand the physical expression of carbonates on log and in seismic data. He was a distinguished lecturer for AAPG (1996/97), Joint Oceanographic Institutions (1997/1998), and the European Association of Geoscientists and Engineers (2005/2006). Gregor T. Baechle University of Miami, Rosenstiel School of Marine and Atmospheric Science, Division of Marine Geology and Geo- physics, 4600 Rickenbacker Causeway, Miami, Florida 33129 Gregor T. Bächle graduated from the University of Tübingen in 1999 with a Diploma (equivalent to M.Sc. degree) in geology. In 2001, he joined the Comparative Sedimentology Laboratory (CSL) with a Scholarship of the German Academic Ex- change Service to obtain a Ph.D. from the Univer- sity of Tübingen. From 2004 to 2008, he was a research associate in the CSL, managing the rock physics laboratory. He is currently working for ExxonMobil Upstream Research Company, Quan- titative Interpretation, Houston, Texas. Copyright ©2009. The American Association of Petroleum Geologists. All rights reserved. Manuscript received January 7, 2009; provisional acceptance March 27, 2009; revised manuscript received May 2, 2009; final acceptance May 27, 2009. DOI:10.1306/05270909001 AAPG Bulletin, v. 93, no. 10 (October 2009), pp. 1297–1317 1297 and separate-vug porosity cannot always be separated using sonic logs, (2) P-wave velocity is not solely controlled by the percentage of spherical porosity, and (3) quantitative pore ge- ometry characteristics can be estimated from acoustic data and used to improve permeability estimates. INTRODUCTION Several attempts have been made to find a rock or pore-type classification that would capture rock texture, pore type, and petrophysical characteristics (Archie, 1952; Choquette and Pray, 1970; Lucia, 1983, 1995; Lønøy, 2006). In this article, we describe a digital image analysis (DIA) method for mea- suring quantitative pore-structure parameters derived from thin sections and introduce four parameters that are most re- liable for capturing the geometrical character of pore struc- ture in carbonates. Many studies have recognized that acoustic velocity in car- bonates is dependent upon pore geometry (Anselmetti and Eberli, 1993, 1997, 1999; Kenter et al., 1995; Wang, 1997; Sun et al., 2001; Eberli et al., 2003; Baechle et al., 2004; Weger et al., 2004; Weger, 2006). In many theoretical studies, the pore aspect ratio is assumed to be the main geometric variable influencing acoustic velocity (Assefa et al., 2003; Saleh and Castagna, 2004; Agersborg et al., 2005; Kumar and Han, 2005; Rossebø et al., 2005). The theoretical concept is that high-aspect-ratio pores, such as molds and vugs, provide more grain-to-grain contact than interparticle and intercrystalline pores, thus decreasing the pore compressibility and provid- ing more stiffness to the rock at equal porosity (Mavko and Mukerji, 1995; Saleh and Castagna, 2004). Consequently, a sequence of rocks with mostly moldic and/or vuggy porosity will have a higher acoustic velocity than a formation with pre- dominantly intercrystalline and/or interparticle porosity with the same amount of total porosity. Many scientists exploited this fact to quantitatively estimate the amount of secondary porosity (Schlumberger, 1972, 1974) and separate-vug po- rosity by modeling porosity from acoustic logs (e.g., Nurmi, 1984; Lucia and Conti, 1987; Wang and Lucia, 1993; Lucia, 1999). This modeling was based on (1) Wyllie’s time-average equation (Wyllie et al., 1956) and (2) the assumption that separate-vug porosity has a minor influence on the acoustic log (Schlumberger, 1972, 1974; Lucia, 1987; Doveton, 1994). Lucia and Conti (1987) and Lucia (1991) calibrated the influ- ence of separate-vug porosity on acoustic logs by point counting separate-vug porosity on thin sections of oomoldic rocks, and Jose L. Massaferro Gerencia Geología y Estudios Integrados, Dirección Exploración y De- sarrollo de Negocio, Macacha Güemes 515, (C1106BKK), Puerto Madero, Buenos Aires, Argentina Jose Luis Massaferro is a geology manager in Repsol YPF’s exploration office in Argentina. He received his Ph.D. from the University of Miami in 1997. He was a Fulbright Fellow while pursuing his studies in Miami. Prior to his Ph.D. studies, he worked for Texaco as a geologist. In 1998, he joined Shell E&P and was involved in different projects, including 3-D seismic volume interpretation, high- resolution sequence stratigraphy, and kinematic modeling of compressional structures. In 2005, he joined Repsol in Madrid. Yue-Feng Sun Department of Geology and Geophysics, Texas A&M University, College Station, Texas 77843 Yue-Feng Sun is an associate professor at Texas A&M University. He received his Ph.D. (1994) from Columbia University. He has 25 years of experience as a geoscientist in the industry and academia. His professional interests include carbonate rock physics, poroelasticity, poroelectro- dynamics, reservoir geophysics, and petroleum geology. He is a member of AAPG, the American Geophysical Union, American Physical Society, and the Society of Exploration Geophysicists. ACKNOWLEDGEMENTS The methodology presented in this paper was developed in collaboration with Shell‘s carbon- ate development team in Rijswijk, Holland, and the Comparative Sedimentology Laboratory of the University of Miami. We acknowledge fi- nancial support from Shell and the Industrial Associates of the Comparative Sedimentology Laboratory. Discussions with Guido Bracco Gartner, Gene Rankey, and Peter Swart were essential to the technical development of the equipment and methodology. Comments and reviews on several versions of the manuscripts by Wayne Ahr, Stephen Ehrenberg, Jerry Lucia, Mark Longman, David Kopaska-Merkel, and Jeroen Kenter greatly improved the manuscript. The AAPG Editors thanks the following reviewers for their work on this paper: Jeroen Kenter, David C. Kopaska-Merkel, and Mark W. Longman. 1298 Geohorizons proposed empirical equations to calculate separate- vug porosity from acoustic transit time. Anselmetti and Eberli (1993, 1997, 1999), however, showed how in carbonates a variety of pore types uploads/Litterature/ weger-et-al-2009-aapgbull.pdf