Factors Controlling Source and Reservoir Characteristics in the Niobrara Shaleoil System, Denver Basin

Originally published as: Han, Y., Horsfield, B., Mahlstedt, N., Wirth, R., Curry, D. J., LaReau, H. (2019): Factors controlling source and reservoir characteristics in the Niobrara shaleoil system, Denver Basin. - AAPG Bulletin, 103, 9, pp. 2045—2072. DOI: http://doi.org/10.1306/0121191619717287 Q:1 Factors controlling source and AUTHORS Yuanjia Han ~ 1 German Research Centre reservoir characteristics in the for Geosciences (GFZ), Telegrafenberg, Potsdam, Germany; Key Laboratory of 2 Niobrara shale oil system, Tectonics and Petroleum Resources, China University of Geosciences, Wuhan, China; 3 Q:2 Denver Basin [email protected]; hanyj@cug. edu.cn 4 Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, Yuanjia Han is a junior professor at China 5 Richard Wirth, David J. Curry, and Heather LaReau University of Geosciences, focusing primarily on hydrocarbon retention and migration processes in unconventional shale systems. He obtained his B.S. and M.S. degrees from 6 ABSTRACT China University of Geosciences and a Ph.D. from the Technical University of Berlin, both 7 This paper clarifies the controls of oil retention in the Niobrara with specialization in integrated petroleum 8 Formation, Denver Basin, in the western United States. Sweet systems analysis. He is the corresponding author. 9 spots have been recognized using a total of 98 core samples from Brian Horsfield ~ 10 5 wells with maturities covering the oil window. Section on Organic Geochemistry, GFZ, Telegrafenberg, 11 Oil retention in the source rock samples (carbonate content Potsdam, Germany; [email protected] 12 <70 wt. %) is controlled by organic matter richness and thermal fi 13 Q:6 maturity. In general, the vaporizable hydrocarbon (HC) yield at Brian Hors eld was a full professor of organic geochemistry and hydrocarbon systems at the 14 nominal temperatures at 300°C (572°F) (Rock-Eval S )is 1 Technical University of Berlin, Germany, as 15 positively correlated to total organic carbon (TOC). With in- · well as leader of organic geochemistry at the 16 creasing maturity, the so-called oil saturation index (S1/TOC GFZ. He is a member of the German Academy fi 17 100) rst increases until a maximum retention capacity (100 mg of Science and Technology. He has more than 18 HC/g TOC) is exceeded at the temperature at the maximum rate 30 years of experience working with and 19 of petroleum generation by Rock-Eval pyrolysis (Tmax)ofap- for industry in upstream research and 20 proximately 445°C (~833°F) and subsequently decreases. The development. The evaluation of gas in place 21 depletion in oil retention capacity is believed to be associated and producibility in unconventional hydrocarbon systems of the United States, 22 with the appearance of organic nanopores. South Africa, China, Australia, and North Africa 23 Oil retention in samples with distinct reservoir potential > are key activities in his service and research at 24 (carbonate 30 wt. %) is controlled by carbonate content, which the present time. 25 Q:7 is positively related to the amount of retained oil (S1). Petro- 26 graphic features indicate that oil or bitumen is stored in porous Nicolaj Mahlstedt ~ Section on Organic 27 calcite fossils (i.e., coccolith and foraminifera), which provide Geochemistry, GFZ, Telegrafenberg, Potsdam, Germany; nicolaj.mahlstedt@gfz- 28 additional space for petroleum storage. Chalk samples (car- potsdam.de 29 bonate >85 wt. %) are characterized by anomalously low Tmax 30 values caused by the influence of heavy petroleum or bitumen. Nicolaj Mahlstedt is a postdoctoral researcher at the GFZ. He studied applied geosciences and Q:3 31 The amount of this bitumen is higher than the initial petroleum holds a diploma and Ph.D. from the Technical 32 potential of kerogen in A and B chalks and thus must have been University of Berlin. He conducted his Ph.D. 33 emplaced here. The most likely sources are juxtaposed organic- within the GFZ–Industry Partnership Program 34 rich marl layers. investigating high temperature methane generation. His major scientificinterests include petroleum system analysis, oil and gas retention processes, compositional kinetic Copyright ©2019. The American Association of Petroleum Geologists. All rights reserved. modeling, and the development of Manuscript received July 12, 2017; provisional acceptance November 14, 2017; revised manuscript geochemical screening tools. received January 9, 2018; revised manuscript provisional acceptance February 6, 2018; 2nd revised manuscript received February 8, 2018; final acceptance January 21, 2019. DOI:10.1306/0121191619717287 AAPG Bulletin, v. nn, no. nn (nn 2019), pp. 1–28 1 Richard Wirth ~ Section on Chemistry Thus, sweet spots occur where carbonate content is either 35 and Physics of Earth Materials, GFZ, low (high TOC)orhigh(lowTOC), whereas production of 36 Telegrafenberg, Potsdam, Germany; wirth@ petroleum from the pore space of presumably brittle chalk seems 37 gfz-potsdam.de more attractive than production from organic- and clay-rich 38 Richard Wirth is a senior research scientist and rocks. 39 laboratory supervisor at the GFZ. He studied mineralogy and electron microscopy and holds a diploma and Ph.D. from the University of Wurzburg.¨ His work is focused on the INTRODUCTION 40 application of advanced electron microscopy (transmission electron microscopy and Shale oil systems are organic-rich mudstone units in which a 41 focused ion beam). significant portion of the generated oil is retained in situ or has 42 migrated into juxtaposed organic-lean rocks (e.g., carbonates) 43 David J. Curry ~ Noble Energy, Inc., (Jarvie, 2012). The Upper Cretaceous Niobrara Formation fits 44 Houston, Texas; David.Curry@nblenergy. com this description perfectly, with a combination of interbedded 45 organic-rich mudstones and relative organic-lean chalks. 46 David J. Curry is a senior geochemical advisor The Niobrara strata were deposited in the Western Interior 47 with the Geoscience Technology Organization at Noble Energy. He received his Ph.D. from Seaway (WIS) during the late Turonian to early Campanian 48 – The University of Texas at Austin in 1981 with a (89 82 Ma) (Da Gama et al., 2014). During that time 49 specialty in organic geochemistry. Since then, (Figure 1A), the WIS stretched from the Arctic Ocean in the 50 he has worked in petroleum systems analysis north, extending through Canada and the United States, all the 51 (basin modeling and geochemistry) in both way to the Gulf of Mexico in the south (Kauffman, 1977). 52 research and exploration positions at several Rhythmic stratification of chalk-marl beds is characteristic of the 53 petroleum companies, including ExxonMobil, Niobrara Formation (Locklair and Sageman, 2008). Brought 54 Q:4 Conoco, Devon, HRT Petroleo, and Noble. about by the variation of siliciclastic input, the rhythmical bed- 55 His interests include nonmarine petroleum ding is believed to have been controlled by eustatic and climatic 56 systems; source-facies depositional processes; kinetics and generation, expulsion, and cycles (Pollastro, 2010). In the Denver Basin, periods of pre- 57 migration processes and their effects on yields vailing cold currents from the Arctic Ocean in the north resulted 58 and fluid properties; and the characterization in the deposition of marls (Luneau et al., 2011; Da Gama et al., 59 of geopolymers. 2014) in which terrestrial detritus was primarily sourced from the 60 western uplifts (Figure 1A). Thus, the Niobrara strata become 61 Heather LaReau ~ Noble Energy, Inc., Denver, Colorado; heatherthegeologist@ progressively siliciclastic to the north, west, and northwest 62 gmail.com; [email protected] (Pollastro, 2010). 63 Stratigraphically, the Niobrara Formation overlies the Carlile 64 Heather L. LaReau is currently the geoscience Q:5 manager for the West Business Unit within BP’s Shale and is overlain by the Sharon Springs Member of the Pierre 65 Lower 48. She received her M.Sc. degree Shale (Figure 1B). The lower limestone part is known as the Fort 66 from McMaster University in 2001 with a Hays Member, and the upper units, namely “A,” B,” and “C” 67 concentration in geoarchaeology, stratigraphy, chalk and marl intervals, are grouped together as the Smoky Hill 68 and radiometric dating methods. In 2007, Member. The chalks and marls are considered as the major hy- 69 she received her Ph.D. from the University drocarbon (HC) reservoirs (Sonnenberg and Weimer, 1993; 70 fl of Wyoming with a focus on uvial Jarvie, 2012; Welker et al., 2013) and source rocks (Landon et al., 71 sedimentology and stratigraphy 2001), respectively. The marls, formed under suboxic-to-anoxic 72 (characterizing avulsion processes in the bottom water conditions (Tanck, 1997; Da Gama et al., 2014), Q:8 73 rock record) throughout Rocky Mountain basins. Her industry career has been are characterized by relatively high contents of type II organic 74 based in Denver, Colorado, working matter (OM) (Luneau et al., 2011; Sonnenberg, 2011). Thermal 75 unconventional oil and gas assets, maturity of the kerogen ranges from immature (thermal stress 76 exploration, reservoir characterization, and equivalent <0.6% vitrinite reflectance [Ro]) in the eastern 77 geochemistry at EnCana, Noble Energy, flank of the Denver Basin to gas-condensate mature (1.4% Ro) 78 ’ and, most recently, BP s Lower 48. Her in the western Wattenberg gas field (Higley et al., 2003; 79 O’Neal, 2015). 80 2 Factors Controlling Source and Reservoir Characteristics in the Niobrara Play 81 Petroleum exploration activities in the Denver Basin date interests include

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