«THERMAL MATURATION-INDUCED EVOLUTION OF THE ELASTIC AND TRANSPORT PROPERTIES OF ORGANIC-RICH SHALES A DISSERTATION SUBMITTED TO THE DEPARTMENT OF ...»
THERMAL MATURATION-INDUCED EVOLUTION OF THE
ELASTIC AND TRANSPORT PROPERTIES OF
SUBMITTED TO THE DEPARTMENT OF GEOPHYSICS
AND THE COMMITTEE ON GRADUATE STUDIES
OF STANFORD UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE
OF DOCTOR OF PHILOSOPHYAdam M. Allan September 2015 © 2015 by Adam Mark Allan. All Rights Reserved.
Re-distributed by Stanford University under license with the author.
This dissertation is online at: http://purl.stanford.edu/vj625gh3300 ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy.
Tiziana Vanorio, Primary Adviser I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy.
Stephan Graham I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy.
Gerald Mavko Approved for the Stanford University Committee on Graduate Studies.
Patricia J. Gumport, Vice Provost for Graduate Education This signature page was generated electronically upon submission of this dissertation in electronic format. An original signed hard copy of the signature page is on file in University Archives.
iii iv ABSTRACT The primary focus of this dissertation is to improve the applicability of rock physics models for elastic anisotropy and ﬂuid transport in organic-rich shale through the development and implementation of practical workﬂows and pioneering experimental methodologies. Shale accounts for the vast majority of rocks in sedimentary basins and, subsequently, the elastic anisotropy of shale must be comprehensively understood for proper processing and interpretation of surface seismic studies. Additionally, as unconventional reservoirs are increasingly targeted, the development of detailed physical relationships between geochemical indicators of hydrocarbon generation and retention with parameters quantiﬁable from remote sensing surveys, such as elastic anisotropy from seismic surveys, are key to improving unconventional exploration procedures and workﬂows. Further, the development of relationships between these geochemical indicators and transport properties, such as porosity and permeability, will be vital to the identiﬁcation of sweet spots and the development of improved recovery eﬀorts in unconventional reservoirs. However, previous attempts at developing these relationships by comparing shale samples from a vast range of formations are suspected to be contaminated by issues of heterogeneity in mineralogy, organic matter type, texture, and burial history between the samples.
In this dissertation, I provide further evidence that relationships developed by comparing samples from multiple formations are obfuscated, or indeed corrupted, by inter-sample heterogeneity. Subsequently, I develop a pioneering methodology for the characterization of a single sample before and after inducing hydrocarbon generation (also called thermal maturation) on individual core plugs. This process is implemented in two manners: ﬁrstly, an experimentally simple method in which samples are thermally matured without any applied conﬁning pressure, and, secondly, an experimentally taxing method in which samples are matured in a purpose-built vessel under in situ conﬁning pressures.
v The ﬁrst lesson learned in this dissertation is that conﬁning pressure must be applied during thermal maturation to preserve the integrity of the sample for future experimental characterization. Without applied conﬁning pressure, the pore pressure induced by hydrocarbon generation can fracture the rock. This fracturing overwhelms any maturation-dependent elastic signature developed in the intact rock matrix, and, as such, renders the sample of little use in developing the complex geochemical-rock physical relationships we desire.
By applying conﬁning pressure during thermal maturation, fracturing is suppressed, and the induced evolution of microstructures and geophysical parameters can be experimentally constrained. Through these experiments, it is determined that the greatest control on organic-rich shale evolution during thermal maturation is the initial microstructure of the thermally immature rock. In organic-rich shales consisting of an aligned siliciclastic matrix and dispersed lenticular organic bodies, hydrocarbon generation and expulsion forms aligned sets of microcracks that, when ﬁlled with ﬂuids, will be acoustically detectable as an increase in elastic anisotropy. Further, the development of these microcracks can result in signiﬁcant increases in the permeability of these samples. Subsequently, thermal maturation of such a laminar shale may be both acoustically detectable and indicate improved production rates. Contrastingly, in organic-rich micritic rocks or siltstones consisting of a weakly aligned matrix and disordered, amorphous organic bodies, microcracks do not align. Subsequently, there is no anisotropic signature of thermal maturation. However, an initial microstructure in which the organic matter occurs as a pore-ﬁlling phase results in severe velocity decreases and permeability increases as that pore-ﬁlling material is expelled from the system. As a result, regions of thermal maturity may be identiﬁable in weakly aligned rocks too, albeit by targeting low velocity zones rather than increases in elastic anisotropy.
I would like to begin by expressing my immense gratitude to my advisers: Tiziana Vanorio for accepting me into her group, supporting me during my time here, challenging and aiding me along the way, and, most importantly, allowing me to repeatedly break equipment in her laboratory; and Gary Mavko for bringing me to Stanford in the ﬁrst place and his remarkably entertaining conversations – for an ornithologist, that is. I would also like to thank Tapan Mukerji for teaching me the vast majority of my computer/programming knowledge and putting up with my early ineptitude in such projects. Finally, I would like to thank Stephan Graham for serving on my committee and correcting numerous issues of misused geologic terminology. Finally-ﬁnally, special thanks to all of the amazing staﬀ in the Department of Geophysics – Tara, Nancy, Fuad, Jared, Michelle, Claudia, Susan, and Vanessa – for being completely awesome and preventing me from being kicked out by forgetting to submit many, many pieces of paperwork.
I am indebted to the William R. and Sara Hart Kimball Stanford Graduate Fellowship for funding the majority of my time at Stanford University and the Stanford Rock Physics and Borehole Geophysics Project for funding the remainder. Furthermore, I am most grateful to ENI S.p.A. and Chevron for providing the majority of the samples studied in this thesis. Perhaps most of all, I am thankful for Tony Clark and his willingness/ability to repair all of the aforementioned broken equipment and his tireless work in designing, building, and maintaining the HTHP. A special thank you is due to my present and former oﬃce mates – Randi, Arjun, Qiang Fu, Dario, Amrita, Ammar, Tony, and Humberto – and all the students and postdocs that I have met in SRB and SRPL over the past 5+ years – Kevin, Richa, Ramil, Ratna, Danica, Piyapa, Adam, Nishank, Fabian, Stephanie, Kenichi, Yu Xia, Chisato, Yuki, Jane, Priyanka, Sabrina, Iris, Natt, Uri, Abrar, Abdullah, Pinar, Salma, Dulcie, and Krongrath (this research group is too big). It was a pleasure to work with, learn from, and have my patience tried by all of you.
vii I have made many lifelong friends during my time in California: Denys, who survived living with me for 3 years while eating theoretically fatal amounts of Jack in the Box, Kevin, who isn’t half bad for a Cardinals fan, Chris, who certainly isn’t the worst Englishman I’ve ever met, Matt for only knocking me oﬀ my bike once, and Nick and Dave who were clearly completely at peace with being inferior golfers to me. I’d be remiss if I didn’t thank Jason, Andreas, and Gader for contributing (likely minimally) to numerous trivia victories, and Ian, Nik, Suzanne, Rall, Sam, Brad, Ossian, Solomon, Jesse, Jens, and Alex for providing... let’s go with levity... along the way. There are likely several hundred other people who deserve to be mentioned here for putting up with my shenanigans for this long, I can only hope this sentence suﬃces.
Finally, I’d like to mention my loved ones. My parents who not only resisted all temptation to put me up for adoption or otherwise sell me, but also supported me deeply with their time and love, but most importantly a roof, warm food, and tuition. My siblings, Kip and Madzi, who, no matter how far I go in life, will always remind me about that one time(!) I slurred onstage.
And my dear Margot, who made up admirably for making me camp in the snows of Yosemite by listening to my (near) constant whining about lab work, shale, experimental science, numerical science, microscopes, lasers, geophysics in general, and a host of other minutiae.
5.1 Schematic ﬂowchart of the experimental workﬂow implemented for iterative shale characterization pre- and post-pyrolysis....................... 132
5.2 Mineralogical composition by weight of the Barnett Shale and Green River outcrop samples...................................... 133
5.3 Representative scanning electron microscopy images of the baseline, immature window microstructures of the Barnett and Green River samples......... 134
5.4 Photographs of the Barnett Shale samples in the immature, oil, and gas windows.135
5.5 Photographs of the horizontally cored Green River sample in the immature, oil, and gas windows.................................... 136
5.6 Time-lapse scanning electron microscopy images of the evolving microstructure of the Barnett and Green River samples between the immature and oil windows. 138
5.7 Time-lapse scanning electron microscopy images of the evolving microstructure of the Barnett and Green River samples between the oil and gas windows.... 139
5.8 Comparison of the eﬀective porosity and grain density values of the horizontal and vertical plugs as a function of thermal maturity................ 141
5.9 The baseline, thermally immature acoustic velocity and elastic anisotropy of the Barnett and Green River samples.......................... 143
6.1 A summary of the mineralogy, average crystallographic orientation, and geochemistry for each sample............................... 177
6.2 The eﬀective porosity and grain density of each permeability subsample..... 177
6.3 Geochemical summary of the Barnett Shale fragments provided by the University of Kiel.
6.4 Mass, volume, eﬀective porosity, and grain density at each stage of thermal maturity........................................ 179
6.5 Geochemical characterization of the pyrolyzed Barnett and Green River samples. 184
6.6 Grain volume, eﬀective porosity, and grain density in the gas window before and after being corrected for residual hydrocarbon content............... 185 6B.1 Permeability measurements and derived continuum permeability and eﬀective pore width values at 13.7 MPa eﬀective pressure for the Barnett Shale samples, pre- and post-pyrolysis................................ 204 6B.2 Permeability measurements and derived continuum permeability and eﬀective pore width values at 20.7 MPa eﬀective pressure for the Barnett Shale samples, pre- and post-pyrolysis................................ 205 6B.3 Permeability measurements and derived continuum permeability and eﬀective pore width values at 27.6 MPa eﬀective pressure for the Barnett Shale samples, pre- and post-pyrolysis................................ 206 6B.4 Permeability measurements and eﬀective pore width values at 1.4 MPa pore pressure, in the gas window, for the horizontally cored Green River sample... 207 6B.5 Permeability measurements and eﬀective pore width values at 1.4 MPa pore pressure, in the gas window, for the vertically cored Green River permeability subsample....................................... 207 6B.6 Permeability measurements and eﬀective pore width values at 1.4 MPa pore pressure, in the gas window, for the vertically cored Green River velocity subsample......................................... 207 6C.1 The numerically simulated continuum permeability and eﬀective pore width as a function of the porosity of the Barnett Shale digital rock geometries...... 208 6C.2 The numerically simulated continuum permeability values and eﬀective pore width as a function of the porosity of the ENI Phase 1 digital rock geometries. 209
1.1 Motivation and Objectives This thesis is concerned, broadly, with the relationship between experimentally obtained velocity and permeability values, microstructure, and thermal maturity for a suite of organic-rich
shales. The experimental analyses that compose this thesis are separable into two main groups: