Paul G. Lillis

Geochemistry of oils from the Junggar basin, northwest China

The Junggar basin of northwestern China is a structural basin containing a thick sequence of Paleozoic-Pleistocene rocks with estimated oil reserves of as much as 5 billion bbl. Analyses of 19 oil samples from nine producing fields and two oil-stained cores in the Junggar basin revealed the presence of at least five genetic oil types. The geochemistry of the oils indicates source organic matter deposited in fresh to brackish lake and marine environments, including coaly organic matter sources. The volumetrically most important oil type discovered to date is produced from Late Carboniferous-Middle Triassic reservoirs in the giant Karamay field and nearby fields located along the northwestern margin of the Junggar basin. Oil produced from the Mahu field, located downdip in a depression east of the Karamay field, is from a different source than Karamay oils. Unique oil types are also produced from an upper Permian reservoir at Jimusar field in the southeastern part of the basin, and from Tertiary (Oligocene) rocks at Dushanzi field and Lower Jurassic rocks at Qigu field, both located along the southern margin of the basin. Previous studies have demonstrated the presence of Upper Permian source rocks, and the possibility of Mesozoic or Tertiary sources has been proposed, but not tested by geochemical analysis, although analyses of some possible Jurassic coal source rocks have been reported. Our findings indicate that several effective source rocks are present in the basin, including local sources of Mesozoic or younger age for oil accumulations along the southern and southeastern margins of the basin. Future exploration or assessment of petroleum potential of the basin can be improved by considering the geological relationships among oil types, possible oil source rocks, and reservoirs.

Assessment of undiscovered oil and gas resources in the Ventura Basin Province, California, 2016

The U.S. Geological Survey (USGS) completed a geology-based assessment of undiscovered, technically recoverable conventional and continuous oil and gas resources in the part of the Ventura Basin Province that lies onshore or within State waters (within 3 miles of the shoreline) of California (fig. 1). Conventional oil and gas resources are those that have migrated upward into structural or stratigraphic traps from deep zones where the oil and gas is generated; water is present below the oil or gas. Continuous accumulations, in contrast, are those in which oil or gas is pervasively present in essentially all wells that penetrate them, that may not be structurally or stratigraphically trapped, and that typically lack oil-water or gas-water contacts. They are commonly produced with well-stimulation technology, such as hydraulic fracturing, referred to as “unconventional.” The same stimulation technology, however, is also used in many conventionally trapped accumulations. We estimated both the likely range of oil and gas volumes remaining to be discovered in accumulations similar to existing conventional oil and gas fields in the Ventura Basin Province (previously assessed by Keller [1995] as 1,060 million barrels of oil [MMBO], 1,900 billion cubic feet of gas [BCFG], and 60 million barrels of natural gas liquids [MMBNGL]), and the potential for oil and gas that might be present in a continuous accumulation at extreme depth in the floor of the basin.

Assessment of undiscovered continuous oil and gas resources in the Monterey Formation, Los Angeles Basin Province, California, 2015

U.S. Department of the Interior U.S. Geological Survey Fact Sheet 2016–3036 July 2016 Printed on recycled paper Oil AU. Conventionally trapped oil and gas fields with oil-water contacts were excluded from the areas of the AUs. Assessment unit boundaries outline the areas in which generation of oil began as the base of the organic-rich Monterey Formation rocks reached burial depths of about 9,000 to 12,000 ft. The Central and Eastern Los Angeles Monterey Continuous Oil AU is defined by the -12,000-foot structure contour near the base of the Monterey Formation, from the map of Wright (1991, fig. 10). The Western Shelf Los Angeles Monterey Continuous Oil AU includes the area west of the Newport-Inglewood fault zone where the base of the Monterey Formation is deeper than 9,000 feet, interpolated from Wright’s (1991) map. Geochemical evidence suggests that the top of this zone may be about 12,000 ft deep in the eastern part of the basin but is likely to be somewhat shallower, about 9,000 ft deep, west of the Newport-Inglewood fault zone where the organic matter in the rocks contains more sulfur, allowing it to generate oil with less heating. Figure 1. Map of the Los Angeles Basin Province in California with boundaries of the two assessments defined in this study. Introduction

Assessment of undiscovered biogenic gas resources, North-central Montana Province

In 2000 the U.S. Geological Survey (USGS) assessed the undiscovered biogenic (also known as microbial) continuous gas resource potential of the North-Central Montana Province in eastern Montana (fig. 1) as part of a national oil and gas assessment project. The assessment was based on the general geologic elements used to define a total petroleum system (TPS), including hydrocarbon source rocks (hydrocarbon generation and migra tion), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this geologic framework, the USGS defined the Cretaceous Judith River through Belle Fourche Biogenic Gas TPS and seven assessment units (AUs) within it, and quantitatively estimated the undiscovered continuous gas resources within each AU. Resource Summary