Sedimentology and reservoir characterization of a shallow-marine to continental transition

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- a case study for Carbon Capture and Storage purposes

Camilla Alterskjær

A thesis submitted for the degree of Master of Science in Geology

60 credits

Department of Geosciences

Faculty of Mathematics and Natural Sciences UNIVERSITY OF OSLO

September 2021

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2021

Sedimentology and reservoir characterization of a shallow-marine

to continental transition - a case study for Carbon Capture and Storage purposes Camilla Alterskjær

https://www.duo.uio.no/

Printed: Reprosentralen, University of Oslo

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Abstract

Outcrop analogs can provide more information about a depositional environment than standard subsurface datasets, which can be used to better understand the sedimentological character of units below seismic resolution. For example, such outcrop data have been used for an ancient shallow marine to continental transitioning analog. The implication of correlating the possible reservoir beds was detected utilizing technical and sedimentological approaches to distinguish the vertical and lateral variability. This information could be used to distinguish heterogeneities of the reservoir unit and implemented for CO₂ sequestration purposes. Modern analogs are added to acquire more information about the prospective depositional environment because such depositional environments are deposited in close proximity to one another and each exhibits a distinct reservoir architecture.

Outcrop data from the Little Grand Wash Fault in Utah, USA, was utilized to create two depositional environment correlations in order to detect heterogeneities in probable reservoir depositional units in shallow marine to continental environments. Further in- vestigation of modern analogs within these conditions has raised plausible consequences within correlation and depositional architecture of such depositional environments that are deposited in close proximity to each other. This study suggests that the selection of an appropriate correlation method is essential to provide information on the depositional environments and their corresponding possible reservoir units.

Keywords: Shallow marine, arid continental, reservoir characterization, sedimentology, outcrop data, correlation panel, depositional environments, Utah, Little Grand Wash Fault, CO2 sequestration

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I want to express my gratitude and sincere appreciation to my main supervisor, Ivar Midtkandal, for your encouragement, motivation, and guidance throughout this process.

Thank you for all of our discussions, the challenges you have given me, and last but not least, your time. I am sincerely grateful. Also, a big thank you to my co-supervisor, Valentin Zuchuat, for all of our discussions, patience, and guidance throughout this process. It has been highly appreciated. A special thanks go to Alvar Braathen for your help and discussion with cross-sections and input on structural geology for my thesis.

It’s been a valuable experience working with my supervisors who have wanted to help me along the way, becoming the best geologist I can be, as well as finding new ways of approaching this thesis under these special circumstances. I couldn’t have asked for better supervisors. I would also like to thank all the people in the COTEC-project for the help provided. Thanks to Elizabeth Petrie from Western Colorado University for your help with providing new data.

A special thanks go to all of my fellow students and friends at the Geosciences, UiO.

You have made this time enjoyable, and I am sincerely grateful for all the help you have given me. Also, thanks to all of my friends and family for your encouragement and support, and always believing in me throughout this time.

Camilla Alterskjær

Oslo, Norway. September 1st, 2021

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Preface

This masters thesis was submitted to the Department of Geosciences at Univer- sity of Oslo (UiO) as a part of the Master of Science in Geosciences (ECTS 120) following the Petroleum Geosciences program. The main supervisor for the thesis was Associate Professor Ivar Midtkandal, Postdoctoral fellow Valentin Zuchuat, and Professor Alvar Braathen.

The data provided in this study are based on previous fieldwork provided from the COTEC-project along with available literature. A field trip to the area was scheduled for autumn 2020, however, it was canceled due to covid-19 travel re- strictions. As a result, facies descriptions and associations are based upon field pictures, sediment logs, Google Earth Pro, virtual outcrop models provided by colleagues of the COTEC-project, and previously published and unpublished research. Several of the logged beds are not supported by field pictures, or structures within the beds are not observable. As a result, it’s critical to remember that these interpretations are based on limited data.

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The four major environments of continental deposits are lacustrine, fluvial, desert, and glaciers (Boggs Jr, 2014). Despite the fact that they are classified into different environments, numerous processes can be found in a single depositional environment, resulting in a more complex depositional succession. These four environments are highly studied individually (e.g., Brodzikowski and van Loon, 1990; North and Prosser, 1993; Anadonet al., 2009), whereas the transition areas from one environment to another has not been as widely studied in the published literature and require additional research.

Separately, shallow marine (Brett, 1995; Siddiquiet al., 2017) and arid environments are thoroughly examined. The sedimentological expression and depositional character of eolian sediments have already been discussed in depth in the literature, and then placed in context with the sedimentary environment (McNight, 1940; Im- lay, 1948; Goudie et al., 1999). In recent years, the external elements that affect the depositional environment for eolian deposits have received increased attention (Pye and Lancaster, 2009).

In the context of CO2 storage sites, it is essential to understand the shallow marine to continental transition setting as these ancient deposits contain suitable reservoir units for injection and storage, with local or regional seals present. Un- derstanding the architectural elements within a reservoir unit is important for CO2

sequestration purposes, where the reservoir unit is desiraby a heterogeneous reservoir (Gershenzon et al., 2015). The heterogenic distribution of the reservoir is key for the spread and migration of the CO2 plume within the reservoir unit (Sundal et al., 2013). To detect such differences within similar depositional units, sedimentary approaches have to be included to provide insight into the depositional environments. To detect such heterogeneities within a potential storage site, sedimentological approaches are prevalent (Ritzi et al., 2016). The lateral and vertical variability within the storage units has to be distinguished to detect the formations’ heterogeneity and the connectivity within the storage units. These lateral and vertical variations are crucial for reservoir characterization within a shallow marine to continental transition. Since the deposits of such environments are deposited in the vicinity of each other, the depositional expression is similar and

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CHAPTER 1. INTRODUCTION

could be interfingering. These kind of features can be detected using well known sedimentological approaches (Walker, 1992), such as facies analysis and correlation panels, raising interpretations on the depositional environment in the studied area.

Finding possible reservoir storage sites, modeling, and correlation of an outcrop analog provide more information than traditional subsurface datasets as these give a deterministic architectural framework of a specific location, rather than giv- ing a wider understanding of the heterogenetic facies distribution of the studied area (Fabuel-Perez et al., 2010). Several approaches can be used to analyse the data provided in an outcrop model, including the application of both theoretical/technical and sedimentological approaches to detect features within the strata and regional aspects. Limitations in the analysis of such datasets can be related to the limited amount of data in the surface and subsurface, the low resolution of the provided data, information gathered form correlation panels, and lack of three dimensional information (Fabuel-Perez et al., 2010). Seismic data usually only reflect the large-scale reservoir architectures and smaller scale features that are of importance to understand the heterogenity of a reservoir unit for CO2 storage purposes can be missing in instances where these are below the seismic resolution.

Seismic acquisition only detects vertical and horizontal architectures no smaller than several tens of meters (Rarity et al., 2014) whilst the features of relevant reservoir units could be down to cm scale. Information on these smaller scale features and the implications of the studied system can be derived from outcrop analysis techniques (e.g., sediment logs, geological maps, and cross-sections) where this can not be provided by seismic data (Rarity et al., 2014). The inherent lim- itation in outcrop data is the lack of three dimensional geological features of the studied area, where the spatial extent of the reservoir architecture is harder to predict (Rarity et al., 2014). Hence, information from the outcrop analysis can be implemented into modern analogs to gain a wider understanding of the three dimensional depositional environment.

Shallow marine to continental transitions in arid environments are detectable in modern analogs that can be applied to the corresponding depositional units in ancient deposits where insight is limited by the available data. In such modern environments, the depositional character of the sediments is similar to what is observed within outcrop or well data with smaller differences in the bedding, which can be crucial for the detectability of the reservoir units. Since these deposits also occur in small areas where the distance from the eolian environment to the open sea is short, the deposited units within these environments are either gradational or could be interfingering. The transition between arid continental (eolian) sedimentation to shallow-marine environments have been described by several other studies, but always in a different context to the focus of this study (Hanebuth et al., 2013; Wang et al., 2016a; Wang et al., 2016b).

Further research into ancient deposits is needed to locate suitable CO2 injection sites, especially if the area has been impacted by tectonic activity. For example,

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if faults are discovered in the vicinity, CO2 may migrate across the fault and seep out into the overburden. As a result, these repercussions must be identified prior to any possible injection.

Along the Little Grand Wash Fault in Utah, USA, an ancient analog with shallow marine to coastal arid environment transition is recognized and outcrop data has been utilized to detect and comprehend features below seismic resolution that are characteristic for these environments. The observations are further put in context with the CO2 seeps found along the Little Grand Wash Fault in Utah, as well as abandoned drill holes (Figure 1.1). Establishing uncertainties within an exposed onshore analog can provide valuable insight where the resolution of the seismic data poses a constraint. Hence, the Little Grand Wash Fault area has become a good analog for CO2 sequestration purposes in similar reservoir units below the overburden.

1.1 Previous work and field area

The COTEC research project examines an onshore analog in Utah (Little Grand Wash Fault). It aims at recognizing apparent hazards below seismic resolution that might occur in nowadays offshore CO2 storage. This includes seeps along faults and probable migration from the footwall to the hanging wall side in a fault.

In addition, the project aims to gather more knowledge on CO2 containment and monitoring techniques. This project is an extended project from the COPASS (CO2 seal bypass) and builds upon this research project from 2015 to 2018.

The WNW trending normal Little Grand Wash fault is situated in east-central Utah, USA, south of Green River and near the San Rafael Swell Monocline (Fig- ure 1.1). This study focuses specifically on exposed strata along the vicinity of Crystal Geyser, ca. 6.7 km south of Green River (Figure 1.1). The exposed formations in the footwall are mainly composed of Jurassic deposits, including the Entrada Sandstone, Curtis Formation, Summerville Formation, and Morrison For- mation. The upper member of the Morrison Formation, Brushy Basin Member, is mostly situated between the fault strands with small sections of Cedar Moun- tain Formation. In addition, Quaternary sediments and Cretaceous strata such as Mancos Shale and Cedar Mountain Formation are exposed in the hanging wall side of the fault (Figure 1.1). CO2 seeps along the fault trace can be detectable as precipitated travertine mounds (e.g., Pentecost, 2005), which evolves from CO2

dissolved within the groundwater (Evans et al., 2004; Kampman et al., 2013).

Three sedimentary logs previously collected from the footwall of the fault and 6 cross-sections perpendicular to the fault across both hanging wall and footwall have been made available for this study.

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CHAPTER 1. INTRODUCTION

Figure 1.1: To the left: overview map of Utah with highlighted locations and larger geological features. Modified after Peterson (1994). To the right: Geologic map from the study area with the location of well CO2W55 and Crystal Geyser. Small yellow clasts in between the fault strands highlights the travertine mounds precipitated from the fault. Q = Quaternary sediments, Kmt

= Mancos Shale, Kcm = Cedar Mountain, Jmb = Brushy Basin Member of Morrison Formation, Jms = Salt Wash Member of Morrison Formation, Jt = Tidwell Member of Morrison Formation, Js = Summerville Formation, Jc = Curtis Formation, Je = Entrada Sandstone. Modified after Petrie (2020).

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The following chapter comprises the tectonic history that has affected Utah, the relation of the tectonic events to the Little Grand Wash Fault, followed by the stratigraphy that covers the footwall and hanging wall side of the fault. Finally, the fault itself is defined and explained as stated by its geometry, tectonic history, and main elements.

2.1 Tectonic history

During the Triassic (251 — 201 Ma), the supercontinent Pangea started to break up and resulted in the opening of the Atlantic Ocean. In this period, North- and South America were also separated (Hintze and Kowallis, 2009) where North America started to drift northwards to latitudes between 30 to 60 degrees North (Fillmore, 2010; Figure 2.1). During the Triassic — Jurassic, Utah migrated from ca. 15^◦to ca. 40^◦North. On the western margin of North America, the Farallon oceanic plate was subducted, creating large volumes of igneous rocks (Christiansen et al., 1994) seen today as the Sierra Nevada volcanic arc (Fillmore, 2010). The continent and the Farallon oceanic plate have been the influencing factor for the Cordilleran Tectonics ever since. The Cordilleran orogenic belt constitutes numerous orogenic episodes, such as the Laramide and Sevier orogenies (DeCelles, 2004).

Several eastward-moving tectonic events since the Mesozoic have contributed to form today’s landscape of Utah (Hintze and Kowallis, 2009).

The Middle Jurassic Elko orogeny (Bajocian — Late Oxfordian, 170 Ma — ca.

157 Ma) (Figure 2.2; T. H. Anderson, 2015) had several alternating extensional and contractional tectonic events (C. H. Thorman and Peterson, 2003). The extent of the orogeny is from central Nevada to Western Utah (C. Thorman, 2011).

The Nevadan Orogeny (Late Jurassic, ca. 153 — 150 Ma; Hintze and Kowallis (2009)) was a brief event in the Late Oxfordian — Kimmeridgian (Schweickert et al., 1984; T. H. Anderson, 2015; Figure 2.2). This orogeny is seen today as granitic intrusions along the Utah-Idaho border (Hintze and Kowallis, 2009).

The Early Cretaceous Sevier Orogeny, which spanned from Paleocene to mid- Eocene, 130 Ma — ca. 45 Ma (Armstrong, 1968; Condon, 2003; Figure 2.2) was

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CHAPTER 2. GEOLOGICAL SETTING

Figure 2.1: Overview of the tectonic phases of the North American continent, and its latitude drift. Phase I: the beginning of plate tectonic in the Archean. Phase II: Uinta intracratonic extension in the Neoproterozoic. Phase III: the Hinge Line from Cambrian to Devonian. Phase IV: Paradox Basin from the Mississippian to Permian. Phase V: Cordilleran Arc from Triassic to Jurassic. Phase VI: Sevier Orogeny in the Cretaceous. From Zuchuat (2019;PhD dissertation), originally modified from Hintze and Kowallis (2009).

an episode of eastward-moving thin-skinned thrust sheets (Condon, 2003; Hintze and Kowallis, 2009). East of the orogeny, a sedimentary basin was developed made up by the sediment load. This sedimentary basin decreased indepth further east.

This orogenic event is one of the main contributors to preserving the Cretaceous strata, both in terms of sediment input and subsidence. It is estimated that this orogenic belt shortened North America in an east-west direction by approximately 100 kilometers (Fillmore, 2010).

The Laramide Orogeny happened from Late Cretaceous — Paleogene in ca. 75 Ma (Condon, 2003; Figure 2.2) is interpreted to have existed due to the subduction of the Farallon Plate beneath the continental plate as this changed to a lower angle and therefore affected the continent more landwards (Fillmore, 2010; Gérault et al., 2015). This led to multiple uplifts and downwarps (e.g., San Rafael Swell) and also reactivation of faults and compressional reverse faults (Hintze and Kowallis, 2009; Fillmore, 2010).

2.2 Basin configuration and stratigraphy

The stratigraphy in east-central Utah encompasses Carboniferous to Quaternary strata, of which the Lower Jurassic to Upper Cretaceous interval is of interest to this study. The Lower Jurassic strata Glen Canyon Group constitutes Wingate Sandstone, Kayenta Formation, and Navajo Sandstone, while the Middle Jurassic San Rafael Group consists of Entrada Sandstone, Curtis Formation, and Sum- merville Formation. Morrison Formation is overlying the San Rafael Group and is a major part of the exposed strata in the footwall of the Little Grand Wash Fault.

The depositional environments of several of these formations in southwestern Utah are presented in Figure 2.3. The Upper Carboniferous deposits are mainly exposed

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Figure 2.2: Overview of the different orogenies in western North America that have impacted the geology in Utah. Modified from C. H. Thorman and Peterson (2003).

in the hanging wall unit and comprise the Cedar Mountain Formation and Mancos Shale (Figure 2.4).

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2.2.1 Glen Canyon Group

The Glen Canyon Group is deposited in the Early Jurassic and consists of Wingate, Kayenta, and Navajo formations. Both the Wingate and Navajo formations are sandstone deposits, while the Kayenta Formation is a fluviatile unit.

Wingate Sandstone

The massive red sandstones of Wingate Sandstone were originally described by Dutton in 1885 and was deposited in the Early Jurassic in the Sinemurian as an eolian erg with intervals of sabkha deposits (Gilluly and Reeside Jr, 1928;

Peterson and Pipiringos, 1979; Fillmore, 2010). The formation is presented in the San Rafael Swell, northwestern Mexico, northeastern Arizona, southern Utah, and moves southeastwards into western Colorado (Gilluly and Reeside Jr, 1928). In the San Rafael Swell area, the formation is ranging between 110 and 122 m thick, and in the study area, CO2 gas and brine are detected at depths of 800 to 900 m (Gilluly and Reeside Jr, 1928; Kampman et al., 2014). The composition of the formation is based on large sandstone intervals with cross-bedding and thin undulating units subsequently representing the erg- and sabkha deposits (Gilluly and Reeside Jr, 1928; Fillmore, 2010). In addition, the "J-0 Unconformity" of Pipiringos and O’Sullivan (1978) is situated at the base of this formation, marking the transition from the Cretaceous to the Early Jurassic (Fillmore, 2010).

Kayenta Formation

The fluviatile Kayenta Formation was deposited in the Early Jurassic in the Plisen- bachian and Toarcian (Peterson and Pipiringos, 1979) and is composed of alternating mudstone and sandstone units described as fluvial channels and eolian deposits (Peterson and Pipiringos, 1979; Hintze and Kowallis, 2009; Fillmore, 2010). The rivers were flowing westwards from the Uncompahagne High in Colorado and were then emptied into a seaway in eastern Nevada (Fillmore, 2010). This formation is interfingering with the overlying Navajo Sandstone (Peterson and Pipiringos, 1979; Fillmore, 2010).

Navajo Sandstone

The Navajo Sandstone was deposited during the late Early Jurassic in the Pliensbachian- Toarcian (180 Ma) (Gilluly and Reeside Jr, 1928; Kocureket al., 2003). The pale- oerg thickens westward (Fillmore, 2010) from less than 100 m in western Colorado to more than 300 m in southern Utah (Dickinson and Gehrels, 2009). In the Utah- Idaho trough, it reaches up to 700 m in thickness and extends over 265 000 km² over five states of the Western Interior (Kocurek et al., 2003). This formation is considered the largest erg deposit ever to have existed (Rodrıéguez-López et al., 2014). It was deposited by the predominant winds blowing southwestward across

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most of the Colorado Plateau during the period of deposition (Peterson, 1988; Pe- terson and Turner-Peterson, 1989; Hintze and Kowallis, 2009; Fillmore, 2010) and represents a dry eolian system (Kocurek et al., 2003). The formation can be recognized by its cross-bedded eolian dune packages that can reach several tenths of meters in thickness. The grain size within the formation usually consists of quartz grains that are fine- to medium size, and these are generally well-rounded (Pe- terson and Pipiringos, 1979; Peterson, 1986, 1994; Fillmore, 2010). Throughout the formation, a few carbonate lenses occur, which were developed in small ponds on the lee side of the large dunes (Peterson, 1986, 1994; Fillmore, 2010). Within these limestone lenses, well-preserved freshwater fossils of invertebrates (ostracods and crustaceans), spores, and pollens were documented and analyzed, as well as bipedal dinosaur traces and early mammals (Fillmore, 2010; Boggs Jr, 2014). The Navajo Sandstone is one of the CO2-charged aquifers in the Little Grand Wash Fault area (Shipton et al., 2004; Kampman et al., 2013; Kampman et al., 2014).

The deposition of the Navajo Sandstone ended presumably when the Carmel Sea transgressed the area, making interdune deposits caused by the marine flooding (Kocurek and Dott Jr, 1983).

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2.2.2 San Rafael Group

San Rafael Group consists of the Carmel Formation, Entrada Sandstone, Curtis Formation, and Summerville Formation (Gilluly and Reeside Jr, 1928).

Carmel Formation

The Carmel Formation was deposited during the Middle Jurassic era (Peterson and Pipiringos, 1979; Doelling, 2001) during the Bathonian (170.1 to 171.4 Ma) (Carr-Crabaugh and Kocurek, 1998; Peterson, 1986; Doelling et al., 2013). The thickness is larger than 200 meters in the northwest and smaller than 30 meters on the east side of Henry Mountains basin (Doellinget al., 2013; Gilluly and Reeside Jr, 1928) and the extent is mostly in the southern and eastern Utah (Sprinkelet al., 2011). This formation is present in the entire Colorado Plateau and thins eastward from 50 m to 12 m (Peterson and Pipiringos, 1979; Doelling et al., 2013). The strata were deposited in a shallow-marine environment with hypersaline intertidal to supratidal conditions, leading to the precipitation of sabkha deposits (Crabaugh and Kocurek, 1993; Fillmore, 2010). In the western part of the Colorado Plateau, it mainly consists of limestone, gypsum, mudstone, and silty sandstone, while in the eastern area, it contains red mudstone and silty sandstone (Peterson, 1994). In the Little Grand Wash Fault area, this formation comprises two members deposited in two different transgressive-regressive cycles, Paria River Member and Winsor Member. In contrast, in the western areas, Carmel Formation holds four different members (Doellinget al., 2013). The formation can be interpreted as a cap rock for the Navajo Sandstone (Peterson and Turner-Peterson, 1989; Dockrill and Shipton, 2010; Kampman et al., 2013). Carmel Formation is marking the limits of the shallow seaway that was present on the eastern side of the Nevadan Orogeny due to the presence of limestone, gypsum, and mudstone (Fillmore, 2010).

Entrada Sandstone

The Entrada Sandstone was deposited during the Callovian (Middle Jurassic; Pe- terson, 1994; Doelling, 2001) and probably up until the early stage of the Ox- fordian (160.8 ± 0.4 Ma; Upper Jurassic; Dossett, 2014). In the Little Grand Wash Fault, the thickness is measured to 150 meters and is thinning towards the west and south to about 125 m (Kampman et al., 2013). This is the second- largest eolian sandstone deposit in North America where the sand came from the north with southward winds (Peterson and Turner-Peterson, 1989; Fillmore, 2010) and represented a wet eolian system that was influenced by a shallow water table (Crabaugh and Kocurek, 1993). There are subunits within this formation: the (informal nomenclature, but commonly used in the literature) earthy facies and the Slick Rock Member (Doelling, 2001). The earthy facies is characterized by red flat-bedded muddy sandstones that are very fine to fine-grained, and the Slick

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Rock Member of the Entrada Sandstone consists of meter to decametre scale red or white alternating cross-bedded sandstone and wavy-laminated silty sandstone (Peterson, 1988; A. J. Newellet al., 2019). The Slick Rock Member is forming the permeable paleoreservoir rock for CO2 fluids and is therefore of huge importance in the Little Grand Wash Fault area (A. J. Newellet al., 2019). Near Little Grand Wash Fault, the Entrada Sandstone displays a heterolithic stratigraphy, with iso- lated coastal dunes, which are aquifers, sandwiched between often-mottled, tight, finer-grained intervals (Kampman et al., 2013; Skurtveit et al., 2020).

Curtis Formation

The Curtis Formation (Gilluly and Reeside Jr, 1928) was deposited during the Late Jurassic in the Early Oxfordian age (161 to 159 Ma) (Imlay, 1948; Doelling, 2001; Wilcox and Currie, 2008). In the San Rafael Swell area, it is between 30 to 60 m thick where it thins out towards the Henry basin in the south and to the southeast towards the Green River (Caputo and Pryor, 1991). The base of the Curtis Formation is defined by the so-called "J-3 Unconformity" (Pipiringos and O’Sullivan, 1978), which name is misleading since it was recently demonstrated to be a diachronous and composite transgressive surface that developed as the Curtis Sea was flooding the Entrada coastal desert during the Oxfordian (ca. 160 Ma) (Zuchuat et al., 2019a, 2019b). It was deposited during a pulsative marine transgressive-regressive cycle (Peterson, 1994; Zuchuatet al., 2018; Zuchuatet al., 2019a). The Curtis Formation is characterized by greenish-gray sandstone, con- glomerates and mudstones, that display evidence of strong tidal influence at the time of deposition (Kreisa and Moila, 1986; Caputo and Pryor, 1991; Wilcox and Currie, 2008; Zuchuat et al., 2018; Zuchuat et al., 2019a), and the greenish color are mostly due to the presence of chlorite and glauconite (Gilluly and Reeside Jr, 1928; Imlay, 1948; Peterson, 1994). Zuchuatet al., 2018 divided it into three different informal units: lower, middle, and upper Curtis. The lower Curtis consists of upper shoreface to beach deposits overlain by subtidal mud-dominated heterolithic succession, which again grade into a sand-dominated subtidal flat. These two are interfingering with a more proximal and shallow sand-rich sub- to supratidal flat and a more distal tidal channel infill. The middle Curtis consists of the characteristic light green to white, very-fine- to fine-grained sandstone appearing as a complex of tidal channels, dunes, and tidal flats. The upper Curtis is a heterolithic subtidal to supratidal deposit together with the continental eolian dune of the Moab Member. Note that only the middle and upper part of the Curtis Formation are present in the study area along the Little Grand Wash Fault, except the Moab Member (Zuchuat et al., 2018).

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Summerville Formation

The Summerville Formation was first named by Gilluly and Reeside Jr, 1928 and was deposited in the early middle Oxfordian (ca. 157 Ma) (Wilcox and Currie, 2008). It was deposited in a marginal marine environment (e.g., hypersaline marine waters and coastal sabkhas) during the Oxfordian, as the Curtis seaway was regressing (Imlay, 1980; Caputo and Pryor, 1991; Fillmore, 2010). The formation can be up to 96 m thick (Peterson, 1988) and the strata are composed of thin-bedded alternating red and brown mudstone and sandstone with frequent precipitation of gypsum and anhydrite beds (Peterson, 1988; Fillmore, 2010). It has been divided into two different members: Chocolate member and Brick-red member by Peterson, 1988. The chocolate member is present in the Little Grand Wash Fault area while the Brick-red member is only present in the western part of the San Rafael Swell, where it was deposited mainly at mudflats and in fluvial environments (Peterson, 1988, 1994).

2.2.3 Morrison Formation

The lower division of the Morrison Formation is correlated with the activity of the Nevadan Orogeny (Peterson, 1986; DeCelles, 2004; Turner and Peterson, 2004).

The Salt Wash distributive fluvial system (DFS) comprises both the Tidwell Mem- ber and the Salt Wash Member of the Morrison Formation. Salt Wash DFS contains a single fluvial system where the distal facies of the Tidwell Member are underlying the proximal facies of the Salt Wash Member (Owen et al., 2015). In the footwall of Little Grand Wash Fault, all the members of the Morrison Forma- tion are present.

Tidwell Member

The Tidwell Member of Morrison Formation was deposited in the Late Jurassic in the Tithonian (Doelling, 2001) and has been dated to 154.75 ± 0.54 Ma, 154.82

± 0.58 Ma, 154 ± 1.4 Ma (Kowallis et al., 1998). This member was formerly a part of the Summerville Formation until Peterson (1988) identified Pipiringos and O’Sullivan (1978) the "J-5 Unconformity" at its base. Similarly to the "J-3 Uncon- formity", the "J-5 Unconformity" is not an unconformity but rather a conformable and time transgressive, as demonstrated by Holland and Wright (2020). The Tid- well Member of the Morrison Formation consists of fluvial and lacustrine facies, which have been described as grayish-green calcareous mudstone around the San Rafael Swell and red mudstone in the western part of the Henry basin (Peterson, 1988; Currie, 1997; Fillmore, 2010; Owenet al., 2015). It is interfingering with the overlying Salt Wash Member as it is a flood plain deposit to these stream channels (Fillmore, 2010; Owenet al., 2015).

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Salt Wash Member

The Salt Wash Member of the Morrison Formation overlay the Tidwell Member and was deposited in the Late Jurassic (Tithonian to Kimmeridgian) (Doelling, 2001). It extends across central Utah, west-central Colorado, northeast Arizona, and northwestern New Mexico (Mullens and Freeman, 1957). It is present in the Colorado Plateau as a coarse-grained fan-shaped fluvial system, including conglom- erate and sandstone deposits. The geometry and composition of the Salt Wash Member testify to the uplift of the areas to the west and southwest of today’s Utah as the Nevadan Orogeny was rising (Fillmore, 2010).

Brushy Basin Member

The mud-dominated Brushy Basin Member of Morrison Formation was deposited in the Late Jurassic (Kimmeridgian to early Tithonian) and has been dated to 152.2

±0.3 Ma in the lowest deposited ash bed, and 150.0±0.5 Ma (Kowalliset al., 1998;

Christiansen et al., 2015). It was deposited in lacustrine, mudflats, and alluvial environments (Peterson, 1994; Currie, 1997), where ashes from the western Sierra Nevada volcanic arc fell onto these environments depositing the largest upper part of the Brushy Basin Member. These are composed of smectitic clays received from the alteration of this volcanic ash, also called tephra (Christiansen et al., 2015).

2.2.4 Upper Cretaceous stratigraphic units

There are two Cretaceous formations located in the down-faulted side of the Little Grand Wash Fault; Cedar Mountain Formation and Mancos Shale.

Cedar Mountain Formation

The fluvial-dominated Cedar Mountain Formation was derived from the eastern part of the Sevier thrust belt flowing westwards across Utah, covering the Colorado Plateau. This formation is composed of two different depositional units; alluvial deposits and high-energy rivers, and floodplain deposits (Fillmore, 2010).

Mancos Shale

The deep-water-dominated Mancos Shale Formation indicates the greatest sea- level rise within the Cretaceous. The deposits are dark gray, organic-rich, and laminated shale, interfingering with thin sand- and siltstone layers and bentonite beds. This formation usually overlies the shallow marine Dakota Sandstone, but within this area, the Dakota Sandstone is not present at all times and it is therefore not included in this study (Fillmore, 2010).

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Figure 2.3: Paleogeographic figures displaying the depositional environments affecting the southwestern USA during the deposition of a) Kayenta Formation, b) Carmel Formation, c) Navajo Sandstone, d) Entrada Sandstone, e) Curtis Formation, and f) Salt wash Member of Morrison Formation. Utah is marked in all figures.

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2.3 Little Grand Wash Fault

The 61 km long fault is located in east-central Utah near the Crystal Geyser, approximately 6 km south of the Green River and 26 km west of San Rafael Swell (Figure 1.1) along with the northern end of Paradox Basin (Shipton et al., 2004;

Evans et al., 2004). It is a WNW trending normal fault downthrown to the south (Campbell and Baer, 1978; Shipton et al., 2004; Dockrill and Shipton, 2010), juxtaposing at the surface Jurassic strata in its footwall to Cretaceous formation in its hanging wall (Figure 2.4; Doelling, 2001). The dip is on average 70^◦ (Dockrill and Shipton, 2010) but can be up to 80^◦ in some areas (Shiptonet al., 2004). The throw was previously considered to reach about 180 to 260 m, (Shipton et al., 2004; Dockrill and Shipton, 2010) but new throw values measured from cross- sections reach roughly 300 m (Oye et al., March 1, 2021), which are similar to the values proposed by McNight (1940). Throw measurements are further discussed in subsection 6.1.3. The fault is segmented into two major semi-parallel fault strands (Shipton et al., 2004; Dockrill and Shipton, 2010) with separation up to 180-210 m (Shipton et al., 2004). Several minor faults accompany these fault strands with different dip angles and directions, creating a complex fault zone. These minor faults are mostly dip-slip with local oblique right and left-lateral movement and are more or less linked up, creating several structural terraces (Figure 2.4; Dockrill and Shipton, 2010).

It is not well understood when the faulting and its deformation happened. Still, it is suggested that it could be related to the uplift of the Green River Anticline, which is situated across the Green River. This anticline is interpreted to be associated with salt movement (Shipton et al., 2004; Dockrill and Shipton, 2010) which started in the Permian and was reactivated several times since then, potentially up until the Quaternary (Evans et al., 2004; Shipton et al., 2004; Dockrill and Shipton, 2010). Furthermore, the Cretaceous formations in the hanging wall are cut by the fault, indicating fault activity at least until this period in time. In addition, faults in the surrounding area have been investigated, suggesting activity until the Tertiary and Quaternary (Chan et al., 2000; Garden et al., 2001) which gives rise to an active period for this fault until then.

Crystal Geyser, located on the east side of the Green River, is an abandoned exploration well (Glen Ruby #1-X) drilled in 1935 that erupts cold water supersat- urated with CO2 with an interval of 4 to 12 hours, leading to the precipitation of rusty colored to white travertine at or near the surface (Doelling, 2001; Evanset al., 2004; Shipton et al., 2004; Dockrill and Shipton, 2010; Frery et al., 2017; Probst et al., 2018; Potter-McIntyre, 2019). Older travertine deposits (400 k.y.) are found where the Little Grand Wash Fault is transecting the fold axis of the Green River Anticline (Figure 2.4; Dockrill and Shipton, 2010; Burnside et al., 2013), where they precipitated following the pressure drops as CO2-rich brine migrating along the fault reached the near surface (Frery et al., 2017). The CO2-charged water is

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most probably erupting from the Lower Jurassic Wingate and Navajo sandstones aquifers (Shiptonet al., 2004; Dockrill and Shipton, 2010; Kampman et al., 2014;

Frery et al., 2017; Probst et al., 2018) and the source of the CO2 is suggested to mainly be contributed to thermal decarbonation of carbonates (Mayoet al., 1991) and also from a reaction between clays and carbonates in, e.g., Paradox Formation (Heath et al., 2009). Wilkinson et al. (2009) also proposes that 0-20% of the CO2

is developed in the mantle.

Figure 2.4: The upper figure represents a geologic map of the Little Grand Wash Fault (LGWF), showing drill hole CO2W55 and Crystal Geyser. The yellow clasts marked in the figure mark the travertine mound precipitated from the fault. The lower figure is a schematic cross-section from A to A’ marked in the geologic map. Abbreviations indicate Q = Quaternary sediments, Kmt = Mancos Shale, Kcm = Cedar Mountain, Jmb = Brushy Basin Member of Morrison Formation, Jms = Salt Wash Member of Morrison Formation, Jt = Tidwell Member of Morrison Formation, Js = Summerville Formation, Jc = Curtis Formation, Je = Entrada Sandstone. *Cross-section is not to scale.

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Methods applied in this study were used to gather results to be generate sedimentological model for reservoir analysis purposes and are presented in section 3.1 in this chapter. This includes logs, cross-sections, facies descriptions and associations, reservoir characteristics, lateral- and vertical extent, and variability. In addition, the relevant theoretical concept of a juxtaposition analysis is presented in section 3.2.

3.1 Sedimentological model for reservoir analysis

The components needed to make a sedimentological model are included in this study, such as facies descriptions, facies associations, reservoir and non-reservoir (net- and non-net-reservoir) characterization, cross-sections, and sedimentary logs.

How these were collected, interpreted, and made is described in this section.

3.1.1 Logging

The logs used in this study are presented in section 4.1 where Log A, B, and C are digitized using Adobe Illustrator for this study. Core logs from CO2W55 have been of much use, respectively, from the Entrada Sandstone (Figure 3.1), while the core logs from Navajo Sandstone and Carmel Formation have been of more use for the reservoir, non-reservoir, and seal analysis (section 5.5). Logs A, B, C, and CO2W55 were correlated using "J-3 Unconformity" as the datum (section 5.3). The horizontal distance between the logs was measured in Google Earth Pro at the "J-3 Unconformity" location. The outcrop model in LIME and Google Earth Pro had too low resolution to distinguish beds. Therefore, the entire correlation is based upon facies associations and field pictures. This dip measured from Google Earth Pro and virtual outcrop model was projected onto Correlation Panel A and used to correlate most of these beds. The largest dip was measured to approximately 9^◦and was more or less used for the entire correlation within this panel. Note that the Summerville Formation is only logged in total in Log C.

Hence, the height of this formation in Log A has been measured from the virtual

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CHAPTER 3. METHOD AND THEORY

Figure 3.1: Overview map with the location of the three logs (blue lines), Little Grand Wash Fault (black lines), travertine mounds (yellow spots), including the log from CO2W55, and Crystal Geyser. The length between the logs is put in red.

outcrop model and in Google Earth Pro from the top Curtis Formation to the "J-5 Unconformity".

There are several approaches towards making these correlation panels according to the nature of the study and the available data. However, since the aim of this study is to generate a sedimentological model, the insight of the depositional history and deposition of the units over time is the focus of these correlation panels (see section 5.3).

3.1.2 Cross-sections

Six N-S-directed cross-sections presented in section 5.4 are made from elevation profiles produced in Google Earth pro v. 2021 (Figure 3.2) and drawn in Adobe Illustrator. Including Google Earth pro v. 2021, different bedrock and interactive maps are used to distinguish the formation boundaries over the area, as well as an overview map of the fault from Petrie (2020). The thicknesses in the subsurface are taken from different literature (e.g., Peterson and Turner-Peterson, 1989

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;Doelling, 2001; Wilcox and Currie, 2008 ;Shipton et al., 2004) and put in Ta- ble 3.1. Interpretations on the fault lenses have previously been investigated and sampled from Bartlett Wash and the Moab Fault due to their presence on the surface (Braathen, 2020). These lenses are projected onto the cross-sections due to the similarity of the fault deformation and the composition of the formations within the Little Grand Wash Fault.

Figure 3.2: Overview figure of the six cross-sections created in N-S direction across the Little Grand Wash Fault.

Table 3.1: Formation thicknesses used in cross-sections.

Formation Thickness (m) Morrison Formation 135 Summerville Formation 47

Curtis Formation 7

Entrada Sandstone 150

Carmel Formation 70

Navajo Sandstone 150

Kayenta Formation 70

Wingate Sandstone 120

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3.1.3 Facies descriptions and facies associations

To determine the different facies and facies association, there are several techniques that can be applied (Walker, 1992). Grain size, structures (ripple marks, nodules/lenses, undulating, amalgamated beds, etc.), color, thickness, bed boundary (erosional, straight, etc.) are investigated within the beds to determine the right facies. Facies associations are determined when two or more facies are re- peated several times vertically. Finally, field photos and sediment logs are used to distinguish the depositional environment of the beds and group them into facies and facies associations.

3.1.4 Reservoir, non-reservoir, and seal descriptions

The reservoir and non-reservoir descriptions are based upon sediment logs and literature. These distinguished reservoirs, non-reservoir, and seal units within the subsurface were utilized for juxtaposition analysis to find the possible migration pathways (section 3.2; section 5.6).

3.1.5 The lateral and vertical extent

The lateral and vertical extent of the potential reservoir formations is examined.

The interactive and bedrock maps are studied in the surrounding area where the formations are present on the surface to get the scope of the subsurface formations.

A few drilled wells are examined to gain an overview of the vertical extent of subsurface formations in the study area (see section 5.8).

3.1.6 Lateral and vertical variability

Logs, facies, facies associations, and literature are applied to understand the lateral and vertical variability of the surface formations in the footwall of the Little Grand Wash Fault.

3.2 Fault Juxtaposition analysis

There are three different types of faults: normal-, reverse- and strike-slip faults. In a normal fault, the hanging-wall side will move downwards, upwards for a reverse fault, and laterally for a strike-slip. According to Pei et al. (2015) there are two types of fault seals: juxtaposition seals and fault rock seals (Figure 3.3). The relative movement of the hanging- and footwall are important in a juxtaposition analysis where units with different lithologies and petrophysical properties (e.g., different porosities, permeabilities, capillary entry pressure) lie beside each other and cause juxtaposition seals (Figure 3.3; Peiet al., 2015). This kind of analysis is important for both hydrocarbon migration and CO2 migration across faults, and also for the entrapment of these two respectively.

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Figure 3.3: Difference between (a) juxtaposition seal and (b) fault rock seal. Modified from Miocicet al.(2019).

A definition of a juxtaposition seal has been described by Allan (1989) and the analysis is used for sealing purposes. The formations are divided into how permeable the different units are, where sandstone units are expected to be more permeable than clay-rich units. There are two characteristic ways to investigate a stratigraphic juxtaposition of the hanging wall and footwall using either an Allan diagram (Figure 3.4; Figure 3.5; Allan, 1989) or a triangle juxtaposition diagram (Figure 3.6; Knipe et al., 1997).

Allan (1989) made a 3D overview model with three assumptions: a fault has no sealing properties, a fault is not an open conduit, and it is the fault juxtaposition that depends on the trapping and migration across a fault (Allan, 1989). The model represents cut-offs from footwall and hanging wall showing spill points and juxtaposition sealing across the fault (Figure 3.4; Allan, 1989).

Knipe et al. (1997) developed a triangle juxtaposition diagram to easier distinguish the different types of fault seals that can form based on the stratigraphic juxtapositions between the hanging wall and footwall.

Both Allan diagram (Figure 3.5) and triangle juxtaposition diagram (Fig- ure 3.6) from the Little Grand Wash Fault area are previously done by Dockrill and Shipton (2010). Approximately 200 different hydrocarbon and water wells, 22 wire-line logs, previous and new field data were used to build these models (Dock- rill and Shipton, 2010; and references therein). Within this study, the reservoir, non-reservoir, and seal analysis will be used to make the juxtaposition analysis.

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Figure 3.4: The principles of Allan Mapping. (a) Juxtaposition seal and migration paths across a fault in cross-section. (b) A 3D model of how the footwall and hanging wall units will juxtapose against each other. (c) The interaction of the units from the footwall and hanging wall in the fault is shown in 2D (Clarkeet al., 2005).

Figure 3.5: Allan diagram over Little Grand Wash Fault redrawn from Dockrill and Shipton (2010). The solid lines represent footwall intersections along both faults and dashed for the hanging wall. The colored zones indicate SGR values at reservoir juxtapositions. Vertical exag- geration x 6. Tc = Chinle Formation, Tm = Moenkopi Formation, Pw = White Rim Formation, Po = Organ Rock Shale

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Figure 3.6: Triangle Juxtaposition Diagram from the study area. Black areas indicate reservoir or seal juxtaposed against the seal, where seals are defined as V_shale>0.5, white shaded areas indicate maximum changes in down-dip throw. In contrast, colored areas represent (a) Shale Gouge Ratio and (b) Shale Smear Factor when the reservoir is juxtaposed against the reservoir.

The vertical blue lines indicate the largest throw on the Little Grand Wash Fault (LGWF) and Salt Wash Graben (SWG), while the vertical purple lines represent maximum surface throw on the Little Grand Wash Fault separated between the fault strands (Dockrill and Shipton, 2010).

Several other factors can control the migration routes and entrapment of hy- drocarbons and CO2 in a fault, such as smearing of clay along the fault. Such other factors have not been investigated in this study. An Allan Diagram is presented in this study and is represented in section 5.6 and further discussed in subsection 6.1.3.

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Data

All of the data provided in this study have been given from previous field trips in the area and were collected without the intention of providing someone else with data for their study. Field pictures taken from these field trips were a large contributor to understanding the different bedding and dividing the sediment logs into several facies and facies associations. The sediment logs (Log A, B, and C) and field pictures were collected from Valentin Zuchuat, where Log A and B have been digitized from field notes for this study. The CO2W55 well was drilled by Shell and has been described in Kampmanet al.(2014), but Valentin Zuchuat has updated this log in Skurtveit et al. (2020), where this publication of the log has been used.

4.1 Sediment logs and supporting stratigraphic informa- tion (pictures, photogrammetry, published data...)

The log from well CO2W55 is collected from Shell (Kampman et al., 2013; Fig- ure 4.3) while log B was collected in 2015, and log A and C were collected in 2019, all done by Valentin Zuchuat (Figure 4.4; Figure 4.5; Figure 4.6). Log A, B, and C are all found east of the Green River, where they are logged in the footwall side of the fault. CO2W55 log is situated west of the Green River in the hanging wall side of the fault (Figure 3.1). These logs were used to make a correlation panel (section 5.3).

4.1.1 CO2W55 logs

Navajo Sandstone

The log from well CO2W55 has recorded approximately 84 m with Navajo Sand- stone containing mostly cross-stratified sandstone beds and bleached sandstone beds Figure 4.1. It is composed of rather homogeneous grain sizes with almost only fine-grained sandstones across the entire formation at this locality.

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Carmel Formation

This 50 m long log collected in well CO2W55 from Carmel Formation contains heterogeneous beds with alternating sand and mud deposits Figure 4.2. The beds include medium, fine, very fine sandstones and silty and muddy deposits.

Entrada Sandstone

This log from well CO2W55 (Figure 3.1; Figure 4.3) is representing the Entrada Sandstone and is almost 87 m. It is previously interpreted and put into different facies and facies associations and is described in Skurtveitet al. (2020). The grain size is ranging from medium to fine to very-fine to silty to clay.

4.1.2 Log A

In Log A (Figure 3.1; Figure 4.4), the Entrada Sandstone, Curtis Formation, and Summerville Formation have been logged where the entire log is approximately 40 m. Entrada Sandstone is logged in the first 7.30 m and contains very fine to fine sandstone beds. Curtis Formation is logged for approximately 4.5 m and comprises mainly fine sandstone beds, with some intercalated mudstone beds. The uppermost 28 m is the Summerville Formation containing mostly very fine and fine sandstone alternating with siltstone beds.

4.1.3 Log B

In Log B (Figure 3.1; Figure 4.5), the Entrada Sandstone is the most logged formation, with Curtis Formation and Summerville Formation above. The entire log is 40.5 m, where the lowermost 28.75 m logged is the Entrada Sandstone consisting of medium, fine, very fine, silty to clay grains. This is followed by approximately 5 to 7 m with Curtis Formation containing very fine, silty, and muddy deposits. The uppermost approximately 5 to 7 m is the Summerville Formation, which contains mostly fine and very fine sandstone, with some upward coarsening beds going from muddy to very fine sandstone. Some of the beds constantly have muddy deposits.

4.1.4 Log C

Log C is 56.25 m and consists of a small section with Entrada Sandstone, a couple of meters with Curtis Formation, while the rest is the Summerville Formation (Figure 4.6). The first 1.75 m is the Entrada Sandstone containing very fine to fine sandstone beds. The next 7.25 m is the Curtis Formation containing very fine sandstone beds. The uppermost 47.25 m represents Summerville Formation, where the uppermost bed is the "J-5" unconformity and marks the boundary between the Summerville Formation and Morrison Formation. Most of the beds are fine sandstones alternating with either very fine sandstone or siltstone beds.

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CHAPTER 4. DATA

Figure 4.1: Log over Navajo Sandstone made from Shell’s well CO2W55 (Kampmanet al., 2013).

Degassing, oil staining, fracture density, and fracture orientation have been included in the figure.

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Figure 4.2: Log over Carmel Formation made from Shell’s well CO2W55 (Kampman et al., 2013). Degassing, oil staining, fracture density, and fracture orientation have been included in

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CHAPTER 4. DATA

Figure 4.3: Log CO2W55 shows only the Entrada Sandstone with facies associations and descriptions explained in Skurtveitet al.(2020).

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CHAPTER 4. DATA

Figure 4.5: Log B with formation boundaries between the Entrada Sandstone, Curtis Forma- tion, and Summerville Formation. The boundary between Curtis Formation and Summerville

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Figure 4.6: Log C with formation boundaries between Entrada Sandstone and Curtis Formation, and Curtis Formation to Summerville Formation.

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Results

This chapter includes all of the results that can be used to make a sedimentological model of the Little Grand Wash Fault. The sedimentological model includes cross- sections, facies descriptions (units in the sediment logs deposited within the same processes), facies associations (several units with multiple facies that occur within the same depositional system), reservoir/non-reservoir characterization, and lateral and vertical variability of reservoir units. The cross-sections are used to make a juxtaposition analysis of the Little Grand Wash Fault. They are represented within this section as a supplement to determine if the fault might be leaking and its importance to determine injection points together with the vertical and lateral extent of the formations and distinct beds from the logs.

5.1 Facies Descriptions

5.1.1 Facies A: Red sandstones with bleaching along with fractures Observed in: Entrada Sandstone (Log A and C), Curtis Formation (Log B), and Summerville Formation (Log B and C)

Description

The beds within Facies A consist of very fine to fine sandstone, with thickness ranging from approximately 0.5 m in Entrada Sandstone, a few centimeters in Curtis Formation, and approximately 1 m in Summerville Formation (Figure 5.1;

Figure 5.2). The beds display high degree of cementation and structureless or plane-parallel stratified to undulating with occasional unidirectional current ripples. Climbing ripples are observed in one of the units (Figure 5.2). Occasional angular shaped 0.5 cm to 1 cm chert nodules are observed in the bleached horizon of the bed (Figure 5.1b). The beds have a reddish color, and most of the beds occur with bleached fractures, while the rest are thin sandstone beds, interfingering between silty deposits. Two sets of different bleaching occurrences are observed in a few of the beds, where one of the bleaching events is seen as yellow bleached zonations, and the others are pale to white (Figure 5.1c).

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Interpretation

Very fine to fine sand and plane-parallel stratification together with current ripples and climbing ripples implies an environment towards the upper flow regime, where the structureless and hard cemented beds signify diagenesis. The thin sandstone layers deposited in Curtis Formation can be interpreted as short periods with aerial exposure. Chert nodules are formed as post-depositional features by fluid flow within the strata. The color of the beds is due to oxidation of iron by subaerial exposure is presumably a continental condition (Boggs Jr, 2014). Several of these beds have experienced fluid migration in the fractured areas where the bleached zoneations are identified. Bleaching in Navajo Sandstone is associated with reduction and removal of hematite (Chan et al., 2000). This reduction might be the reason for the bleaching along the fault within these beds in Entrada Sand- stone and Summerville Formation. Bleached beds can help evaluate reservoir and non-reservoir units as they provide information about the petrophysical properties of the unit. The fact that two sets of bleaching are recognized in these beds implies the occurrence of at least two bleaching episodes associated with the fluid flow along with the open fractures.

Figure 5.1: Field pictures from the respective section of log A from Entrada Sandstone with Facies A. a) An overview picture of different beds in Entrada Sandstone. Pictures b) and c) represent outlined beds with bleached layers in reddish material, where also the bed in picture c) has an additional yellow bleached horizon.

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CHAPTER 5. RESULTS

Figure 5.2: Bleached areas are outlined with dashed lines and arrows. Sections from sediment log C are represented on the right side of the field pictures with arrows towards the respective beds in the sediment log. a) Field picture and sediment log from Entrada Sandstone where both Facies A and B are represented, while b) represents the Summerville Formation with Facies B on the top, Facies A in the middle, and Facies C beneath.

5.1.2 Facies B: Plane-parallel stratified beds

Observed in: Entrada Sandstone (Log A, B, and C), Curtis Formation (Log A and B), and Summerville Formation (Log A, B, and C)

Description

These plane-parallel stratified beds are very fine to fine sandstone or siltstone with a minor amount of mud, with thickness’ varying between 5 cm to 1 m (Figure 5.2;

Figure 5.3). Several sedimentological features are detected, such as scattered

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unidirectional-current ripples and climbing ripples. Soft deformation structures and a few centimeters wide scattered sand lenses are detected in a few beds. The plane-parallel stratified siltstones are brown to reddish, while those composed of sand are light-colored in Entrada Sandstone and reddish in Summerville Forma- tion. A few beds are observed as green and pink. Several beds are bleached, have bleached horizons or patches, or are a part of a larger bleached unit. The plane- parallel stratified beds usually alternate with Facies A or Facies M (immature paleosol), and a few alternates with undulating sandstones.

Interpretation

The plane-parallel stratification of sandstone beds usually reflects high energy periods, while deposition of silty grains reflects a lower flow velocity than the sand (Hjulstrom, 1955). Climbing ripples are deposited when the sedimentation rate is higher than the migration since the flow energy decreases and the sediment is deposited at a high rate (Dalrymple and James, 2010). The detected unidirectional- current ripples from field photos do not have distinguishable foresets. Therefore, these can be interpreted as wind ripples because the wind frequently reworks the ripple’s stoss side, making the foreset hard to detect. Due to the deposition of both current ripples and climbing ripples, the energy within this period could not be too high as these features would not be deposited or would be eroded. The reddish color of the beds is due to oxidation of iron by subaerial exposure in probable continental conditions (Boggs Jr, 2014) where the green color of the bed can either be a form of diagenesis as reducing pore waters can change the color of the bed from red to green (Nichols, 2009), or the presence of glauconite in the bed implicate that it never was red in the first place. Occurrence of soft-sediment deformation and bleaching are all occurring within plane-parallel stratified very fine to fine sandstones. The soft-sediment deformation and the bleaching indicate the presence of fluids within the unit, where the soft-sediment deformation symbolizes fluid within the unit as the bed was deposited. These kinds of structures might also indicate rapid deposition (Tucker, 2011). In contrast, bleaching indicates fluids migrating through the bed after deposition. Both soft-sediment deformation and bleaching of the beds indicates post-depositional features.

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CHAPTER 5. RESULTS

Figure 5.3: Field picture from Entrada Sandstone and a section from sediment log B. The lower outlined unit represents facies B, while the upper outlined unit represents facies E. The mottling structures can be observed as white horizontal patches within the outlined bed of facies B.

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5.1.3 Facies C: Plane-parallel stratified to undulating siltstone

Observed in: Curtis Formation (Log B and log C) and Summerville Formation (Log C)

Description

In Facies C, the beds are composed of silt to very fine sand with plane-parallel stratification to undulating geometry (Figure 5.4). The vertical thickness ranges from 10 cm to 75 cm. All of the beds are reddish, where one of the units is bleached and has rare and scattered current ripples and an orange horizon with purple strain. Small bleached patches are observed beneath the orange horizon with the purple strain (Figure 5.4b). The facies are alternating with fine to coarse sandy units of facies A flaking out of the bed (Figure 5.4a).

Interpretation

Plane-parallel stratification to undulating geometry within silty grains represents an environment towards the upper flow regime. The flow is slow enough to deposit silty grains and high enough to make a plane-parallel stratified to an undulating sequence. Current ripples also indicate deposition within the lower flow regime (Hjulstrom, 1955). The purple strain in the orange horizon reflects paleosol deposit, substantiated with the bleached patches beneath presumably caused by organic acid percolating and small roots. The reddish color of the beds and the orange horizon with purple strain indicates deposition in an arid continental condition. The reddish color, the grain size, and orange horizon with purple strain can indicate wind in a quite damp environment as the primary depositional process of these beds, and the presence of occasional scattered current ripples might reflect a short-lived damp environment or a little pond.

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CHAPTER 5. RESULTS

Figure 5.4: Plane-parallel stratified to undulating siltstone beds. a) Displays an alternating sequence of plane-parallel stratified to undulating beds and facies A. Thin beds from facies A can be recognized flaking out of the cliff face. b) Figure of the orange horizon with purple strain within the plane-parallel stratified to undulating strata.

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5.1.4 Facies D: Undulating sandstone

Observed in: Entrada Sandstone (CO2W55 and Log B) and Summerville Forma- tion (Log C)

Description

Facies D consists of very fine to fine sandstone with either continuous undulated internal structured beds with a wavelength of approximately 1 cm or plane-parallel stratified to undulating beds (Figure 5.5; Figure 5.6). The bedsets range from a few centimeters to 1.5 m, where the internal undulating beds can range up to 15 cm, and the lateral extent of the entire bed is approximately 100 m. A few scattered unidirectional-current ripples and soft deformation structures are found within the beds (Figure 5.5), including a few millimeter thick blue patches, subround to round firmly cemented nodules with a diameter of >1 cm, sand lenses, and chert nodules (Figure 5.6). The chert nodules are not distinguishable in field photos. All of the beds are reddish in Entrada Sandstone and pale in Summerville Formation. These alternates with clay-rich siltstones, plane-parallel stratified beds, or mottled beds.

Interpretation

Internal undulation can either be explained as deformation from sediment load or supercritical flows. The unidirectional current ripples are formed from winds. At the same time, soft deformation structures are explained as fluid escape structures as the sediment load of the overburden compressed the bed and discharged the fluids. These beds are predicted to be deformed due to the rather low wavelength and the occurrence of soft deformation structures. Blue patches can have their occurrence from halite minerals, where sodium nanoparticles interact, forming this color (Calas et al., 2021). Chert nodules and cemented nodules testify to episodes of post-depositional fluid-flows within the strata, where the fluid may have cemented the nodules more than the enclosing sandstone. The Entrada Sandstone beds include wind-driven unidirectional-current ripples and soft-sediment deformation structures, implicating deposition from wind and is interpreted as loess deposits.

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CHAPTER 5. RESULTS

Figure 5.5: The figure represents a soft deformation structure found in Entrada Sandstone, highlighted within the black box. The sediment log is displayed on the right side with a facies column. This section is presumably an ancient stromatolite deposit.

Figure 5.6: Field picture displaying undulating sandstones alternating with amalgamated sandstones and thin beds of clay-rich siltstones. firmly cemented nodules can be recognized in the field picture as subrounded pale patches standing out of the cliff face.

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5.1.5 Facies E: Ripple laminated sandstone

Observed in: Entrada Sandstone (CO2W55 and Log B), Curtis Formation (Log A and Log B), and Summerville Formation (Log B and C)

Description

These beds consist of very fine to fine sandstones (Figure 5.7) ranging from approximately 0.5 to 1.5 m in Entrada Sandstone and 6 cm to 75 cm in Curtis and Summerville Formation. The units are composed of climbing ripples with a thickness of a maximum of 0.5 cm. Sedimentary features such as herringbone cross-stratification and rounded millimeter thick chert nodules are present in a few beds (Figure 5.7b). The beds are light-colored in Curtis and Summerville formations and reddish in Entrada Sandstone. The beds alternating with Facies B are 50-60 cm thick and bleached on the top of the beds (Figure 5.3) while the remaining beds do not alternate with any distinct facies.

Interpretation

All of these beds are composed of climbing ripples, which can indicate a higher sedimentation rate compared to the migration and produces steep angles of climb (Dalrymple and James, 2010). The formation of herringbone cross-stratification is due to current reversals and is often used as a tidal indicator. Interpretation of these deposits can either be within a wet interdune (Kamola and Chan, 1988), deposition on the dry flanks of dunes, or low-lying eolian sand sheets where dunes were absent (A. J. Newell et al., 2019).

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CHAPTER 5. RESULTS

Figure 5.7: Two different beds with rippled laminated sandstone. a) Ripple laminated sandstone bed highlighted with red lines where the bed is covered. A few ripples are highlighted in the figure.

b) Ripple-laminated sandstone composed of climbing ripples with highlighted chert nodules.

Sedimentology and reservoir characterization of a shallow-marine to continental transition - a case study for Carbon Capture and Storage purposes