Petroleum Systems and Geologic Assessment of Oil and Gas in the San Joaquin Basin Province, California Chapter 11 Source-Rock Geochemistry of the San Joaquin Basin Province, California By Kenneth E. Peters, Leslie B. Magoon, Zenon C. Valin, and Paul G. Lillis HIO for all source-rock units except the Tumey formation of Contents Atwill (1935). Abstract-----------------------------------------------------------------------------------1 Thick, organic-rich, oil-prone shales of the upper Mio- Introduction------------------------------------------------------------------------------ 1 cene Monterey Formation occur in the Tejon depocenter in Methods----------------------------------------------------------------------------------2 the southern part of the basin with somewhat less favorable Discussion--------------------------------------------------------------------------------3 occurrence in the Southern Buttonwillow depocenter to the Upper Miocene Antelope shale---------------------------------------------------3 north. Shales of the upper Miocene Monterey Formation Eocene Tumey formation-----------------------------------------------------------4 Eocene Kreyenhagen Formation--------------------------------------------------4 generated most of the petroleum in the San Joaquin Basin. Cretaceous-Paleocene Moreno Formation--------------------------------------5 Thick, organic-rich, oil-prone Kreyenhagen Formation source Conclusions----------------------------------------------------------------------------- -5 rock occurs in the Buttonwillow depocenters, but it is thin Acknowledgments-----------------------------------------------------------------------6 or absent in the Tejon depocenter. Moreno Formation source References Cited------------------------------------------------------------------------ 6 rock is absent from the Tejon and Southern Buttonwillow Figures------------------------------------------------------------------------------------ 9 Tables------------------------------------------------------------------------------------27 depocenters, but thick, organic-rich, oil-prone Moreno For- mation source rock occurs northwest of the Northern Button- willow depocenter adjacent to the southern edge of Coalinga field. Abstract Introduction Source-rock thickness and organic richness are impor- The purpose of this work is to determine the regional tant input parameters required for numerical modeling of extent, burial depth, thickness, and original organic richness the geohistory of petroleum systems. Present-day depth and of petroleum source rocks in the San Joaquin Basin Province thickness maps for the upper Miocene Monterey Formation, of California. These source rocks include the upper Miocene Eocene Tumey formation of Atwill (1935), Eocene Kreyen- Antelope shale of Graham and Williams (1985; hereafter called hagen Formation, and Cretaceous-Paleocene Moreno Forma- Antelope shale), shales of the Eocene Tumey formation of tion source rocks in the San Joaquin Basin were determined Atwill (1935; hereafter referred to as the Tumey formation), using formation tops data from 266 wells. Rock-Eval pyroly- shales of the Eocene Kreyenhagen Formation, and shales of sis and total organic carbon data (Rock-Eval/TOC) were the Cretaceous-Paleocene Moreno Formation. Figure 11.1 is collected for 1,505 rock samples from these source rocks in a generalized stratigraphic column for the San Joaquin Basin 70 wells. Averages of these data for each well penetration that identifies these principal petroleum source rocks, as well as were used to construct contour plots of original total organic principal reservoir rocks. Organic richness can be described by carbon (TOCo) and original hydrogen index (HIo) in the measures of the quantity (total organic carbon, TOC) and qual- source rock prior to thermal maturation resulting from burial. ity (Rock-Eval pyrolysis hydrogen index, HI) of organic matter Sufficient data were available to construct plots of TOCo and in samples of source rocks (Peters and Cassa, 1994). 2 Source-Rock Geochemistry of the San Joaquin Basin Province, California The formal names for petroleum systems consist of the others, this volume, chapter 8). Geological and geochemical source rock name, followed by a hyphen, the principal reser- evidence suggests that the Moreno Formation source rock voir name, and an indication of the certainty of the correlation accounts for the Oil City pool (Peters and others, 1994), but (Magoon and Dow, 1994). The symbols (?), (.), and (!) indi- an attempt to correlate the oil with pyrolyzed Moreno Forma- cate speculative, hypothetical, and known genetic relation- tion (Marca Shale Member) source rock was not convincing ships, respectively. Geochemical correlation, which might (Fonseca-Rivera, 1998). include biomarker and stable carbon isotopic comparison of source-rock extracts with crude oils (Magoon and Dow, 1994; Peters and others, 2005), is needed for a system to be termed Methods known (!). As suggested by Graham and Williams (1985) and Beyer and Bartow (1987), recent geochemical studies Figure 11.2 is an index map that shows the locations of show that the two principal source rocks for petroleum in the wells in the study area that had depth and thickness data; these San Joaquin Basin consist of the upper Miocene Antelope data were used to construct figures 11.4 through 11.10. Figure shale member of the Monterey Formation and shales of the 11.3 is an index map that shows locations of wells with Rock- middle to upper Eocene Kreyenhagen Formation (Kaplan and Eval pyrolysis and total organic carbon (TOC) data; these others, 1988; Peters and others, 1994; Lillis and Magoon, this data were used to construct figures 11.11 through 11.16. The volume, chapter 9). The Antelope-Stevens(!) petroleum system thickness, TOC, and Rock-Eval hydrogen index contour maps (described as the McLure-Tulare(!) north of the Bakersfield were created using ArcInfo® (Version 8.1.2), a commercial Arch) accounts for about 12.2 billion barrels of oil (BBO) and Geographic Information System (Environmental Systems 13.1 trillion cubic feet of gas (TCFG), while the Kreyenhagen- Research Institute, Redlands, California). Temblor(!) petroleum system accounts for about 1.8 BBO Source-rock burial depth (figs. 11.4 through 11.7) and and 3.0 TCFG in the basin (Magoon and others, this volume, thickness maps (figs. 11.8 through 11.10) were constructed chapter 8). using well log data from 266 wells correlated on six regional Crude oils from Antelope shale and Kreyenhagen Forma- cross sections published by the Pacific Section of the Ameri- tion source rocks are readily distinguished by their 13C-rich can Association of Petroleum Geologists (PS-AAPG, 1957a,b, (δ13C -22 to -25‰) and 13C-poor (δ13C -28 to -30‰) carbon 1958a,b, 1959, 1989). Using these data, the distribution, isotope compositions, respectively (Peters and others, 1994). depth, and thickness of the Antelope shale, Tumey formation, These differences reflect an abrupt change in the isotopic com- Kreyenhagen Formation, and Moreno Formation source rocks position of source-rock kerogen near the Paleogene-Neogene were constrained by 82, 71, 79, and 34 wells, respectively boundary. Marine algal kerogen is depleted in 13C compared (tables 11.1 through 11.4). The top and bottom of each source to that derived from terrigenous kerogen in Paleogene and rock were determined from the PS-AAPG cross sections older rocks, whereas it is enriched in 13C compared to ter- using the following general criteria and unit names. The top rigenous kerogen in Neogene and younger rocks (Arthur and of the Antelope shale was equated with the top McLure Shale others, 1985). Lillis and Magoon (this volume, chapter 9) Member of the Monterey Formation, the “N” point electri- show isotope and biomarker evidence that supports these two cal marker, or top Mohnian age units, depending on the cross major petroleum systems. These isotopic differences extend section location. The base of the Antelope shale was equated to the products of kerogen in oil field waters. For example, with the top Temblor Formation, top Devilwater Shale and short-chain C2-C5 organic acids generated from kerogen during Gould Shale intervals (both members of the Monterey Forma- burial migrate with oil field waters and have aliphatic carbon tion), or top of Luisian age units (fig. 11.1). The McDonald atoms with stable carbon isotope ratios that fall in the ranges Shale Member of the Monterey Formation was included in the -22.5 to -25.6‰ and -27.8 to -29.8‰, reflecting the two major Antelope shale interval. The Tumey formation lies at the top sources of crude oils in the basin (Antelope shale and Krey- of the Kreyenhagen Formation or at the base of the Refugian enhagen Formation source rocks, respectively) (Franks and age units. The top of the Tumey formation coincides with the others, 2001; Dias and others, 2002). base of the Cymric Shale Member of the Temblor Formation, The Tumey-Temblor(.) petroleum system accounts for 0.6 the Leda sand of Sullivan (1963), or the base of Zemorrian age BBO and 2.1 TCFG in the San Joaquin Basin (Magoon and units (fig. 11.1). The top of the Kreyenhagen Formation occurs others, this volume, chapter 8). Unlike the other petroleum below the Tumey formation or Oceanic sand of McMasters systems in this study, the Tumey-Temblor(.) petroleum system (1948). The bottom of the Kreyenhagen Formation coincides is hypothetical because no definitive geochemical correlations with the top of the Domengine Sandstone, Gatchell sand