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  • 1
    Language: English
    In: Marine and Petroleum Geology, 2014, Vol.56, p.255(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.marpetgeo.2014.02.013 Byline: Barry Katz, Fang Lin Abstract: There has been a revival in hydrocarbon source rock characterization and development associated with growing interest in unconventional resources, where these fine-grained organic-rich rocks act as both source and reservoir. To-date, the exploration focus on shale reservoirs has been largely on marine systems. Lacustrine source rocks for conventional resources are geographically important, dominating regions such as China, Indonesia, and Brazil's resource-base. However, they have been generally untested for unconventional resources. There are a number of key differences in the nature of these hydrocarbon systems that should be considered when assessing whether lacustrine systems may represent future unconventional opportunities in areas where the conventional resource-base is dominated by lacustrine-sourced oil. Among the key differences between these depositional systems is the greater sensitivity to high frequency climatic variability within lacustrine systems. Lacustrine systems are highly sensitive to changes in the balance between precipitation and evaporation, which may lead to rapid changes in lake level, potentially exceeding 600 m. These changes in depositional conditions are geologically rapid and may occur over periods of thousands of years. Such changes can reduce the areal extent of potentially thick source rock intervals to only those portions of a basin where a permanent deep lake was present. Thus the core unconventional target area may be geographically limited compared with their marine counterpart. Although potentially areally limited, a review of many lacustrine source rocks suggests that their thicknesses are often significantly greater than marine source rocks. An examination of the more distal portions of lacustrine systems, where better source rock potential is present reveals that there is generally limited connectivity between source and conventional reservoir. In these settings, such as the Wind River basin (Waltman Shale), the hydrocarbons remain trapped within the shales, potentially leading to over-pressured hydrocarbon charged systems. Such conditions suggest that although areally limited, viable unconventional targets may exist, if suitable reservoir conditions are present. Finally, the character of the oils produced is different in these settings, with lacustrine oils being waxy and displaying different hydrocarbon generation and cracking kinetics. High wax oils display distinct flow characteristics, being more viscous, and may offer different production challenges than their non-waxy marine equivalents. Additionally, differences in their cracking kinetics may indicate that the timing of gas generation for shale gas plays may differ significantly from marine systems. Author Affiliation: Chevron Energy Technology Company (ETC), Houston, TX 77379, USA Article History: Received 29 October 2013; Revised 16 February 2014; Accepted 20 February 2014
    Keywords: Rain ; Shale Oils
    ISSN: 0264-8172
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Marine and Petroleum Geology, May 2018, Vol.93, pp.409-421
    Description: Petroleum migration modeling is widely used to assess petroleum charge and fluid phase risk in exploration and appraisal. There are three principal migration methods: Darcy flow, invasion percolation, and flowpath (or ray tracing). Each method relies on different assumptions and yields different outcomes. This paper analyzes the strengths and weaknesses of these methods as they are implemented in PetroMod , providing a practical guide as to how and when to apply each migration method. Flowpath is the most simplistic and computationally fastest method and should only be applied when a quick screening is required. Invasion percolation delivers satisfactory results for most geological settings, from structurally and stratigraphically simple to complex, but does not consider expulsion from the source rock properly. Darcy flow is the preferred method for unconventional resource assessments and supports maximum downward migration. A traditional modeling approach is to use two methods, applying Darcy flow to tight rocks and flowpath to highly permeable rocks. Another combined method can be used in such a way that Darcy flow is applied to the source rock and invasion percolation to the carrier and reservoir beds. The latter seems to deliver best results in most geological settings, while also providing more realistic results of secondary migration losses.
    Keywords: Petroleum Geology ; Petroleum ; Basin Modeling ; Migration ; Darcy ; Flowpath ; Invasion Percolation ; Engineering ; Geology
    ISSN: 0264-8172
    E-ISSN: 1873-4073
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  • 3
    Language: English
    In: Marine and Petroleum Geology, September 2014, Vol.56, pp.255-265
    Description: There has been a revival in hydrocarbon source rock characterization and development associated with growing interest in unconventional resources, where these fine-grained organic-rich rocks act as both source and reservoir. To-date, the exploration focus on shale reservoirs has been largely on marine systems. Lacustrine source rocks for conventional resources are geographically important, dominating regions such as China, Indonesia, and Brazil's resource-base. However, they have been generally untested for unconventional resources. There are a number of key differences in the nature of these hydrocarbon systems that should be considered when assessing whether lacustrine systems may represent future unconventional opportunities in areas where the conventional resource-base is dominated by lacustrine-sourced oil. Among the key differences between these depositional systems is the greater sensitivity to high frequency climatic variability within lacustrine systems. Lacustrine systems are highly sensitive to changes in the balance between precipitation and evaporation, which may lead to rapid changes in lake level, potentially exceeding 600 m. These changes in depositional conditions are geologically rapid and may occur over periods of thousands of years. Such changes can reduce the areal extent of potentially thick source rock intervals to only those portions of a basin where a permanent deep lake was present. Thus the core unconventional target area may be geographically limited compared with their marine counterpart. Although potentially areally limited, a review of many lacustrine source rocks suggests that their thicknesses are often significantly greater than marine source rocks. An examination of the more distal portions of lacustrine systems, where better source rock potential is present reveals that there is generally limited connectivity between source and conventional reservoir. In these settings, such as the Wind River basin (Waltman Shale), the hydrocarbons remain trapped within the shales, potentially leading to over-pressured hydrocarbon charged systems. Such conditions suggest that although areally limited, viable unconventional targets may exist, if suitable reservoir conditions are present. Finally, the character of the oils produced is different in these settings, with lacustrine oils being waxy and displaying different hydrocarbon generation and cracking kinetics. High wax oils display distinct flow characteristics, being more viscous, and may offer different production challenges than their non-waxy marine equivalents. Additionally, differences in their cracking kinetics may indicate that the timing of gas generation for shale gas plays may differ significantly from marine systems.
    Keywords: Cracking Kinetics ; Fracability ; Generation Kinetics ; Lake Level ; Shale Gas ; Shale Oil ; Waltman Shale ; Wind River Basin ; Engineering ; Geology
    ISSN: 0264-8172
    E-ISSN: 1873-4073
    Source: ScienceDirect Journals (Elsevier)
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  • 4
    Language: English
    In: Marine and Petroleum Geology, May 2016, Vol.73, pp.492-516
    Description: The radiation of land plants at the onset of the Devonian resulted in a change in the character of available biomass, which in turn, introduced changes to the nature of petroleum systems. This study examines the nature of pre-Devonian petroleum systems prior to this significant evolutionary event. Conventional hydrocarbon resources have been associated with pre-Devonian petroleum systems across the globe, including the Neoproterozoic–Infracambrian Huqf Supergroup of the Oman basin, the Riphean–Vendian sequences of East Siberia, the Cambrian of the Murzuq basin, the Ordovician of the Tarim basin, and the Silurian Qusaiba of Saudi Arabia. Although individual accumulations can be quite significant (e.g., Hassi Messaoud has ultimate recoverable reserves of ∼10 billion barrels), the relative importance of pre-Devonian-derived oils is thought to be limited compared to the global conventional resource-base. With growing interest in unconventional resources, the relative importance of these systems is expected to increase as resource plays such as the Ordovician Utica Shale of the Appalachian basin, the Cambrian of China, and possibly the Silurian of Central and Eastern Europe develop. The advanced ages of these systems result in some unique properties and amplify risks that exist in younger petroleum systems. Differences in the nature of the biomass contributing to pre-Devonian source rocks may give rise to oils that display unique geochemical characteristics. For example, there are some Precambrian oils where C steranes dominate even though land plants were absent. There are also Ordovician source rocks dominated by , a primitive prokaryote, which yield oils containing limited amounts of C components and nearly lack pristane and phytane. The potential for unconventional reservoirs in pre-Devonian systems may also be highly dependent upon the age of the system, as biological evolution influences the availability and nature of biogenic silica, an important factor controlling brittleness and fracability. Literature has shown that biogenic silica from different sources displays varying degrees of resistance to diagenesis, which allows the formation of a silica network and influences brittleness. For example, radiolaria present during the Cambrian are more resistant to diagenesis than diatoms, which did not evolve until the Jurassic. Risks associated with preservation of hydrocarbons are also amplified in pre-Devonian petroleum systems. Many such systems have been exposed to significant thermal stresses, resulting in the cracking of oil and wet gas. Others have had complex tectonic histories potentially resulting in the breaching of seals or changes in PVT conditions that can result in gas loss. Gas loss may also occur through diffusion from these older reservoirs as a result of long residence times.
    Keywords: Exploration Risk ; Unconventional Resources ; Hydrocarbon Preservation ; Hassi Messaoud ; Verkhnechonskoye ; Marmul ; Tahe ; Utica Shale ; Engineering ; Geology
    ISSN: 0264-8172
    E-ISSN: 1873-4073
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  • 5
    Language: English
    In: Marine and Petroleum Geology, 2002, Vol.19(6), pp.783-796
    Description: The South Caspian basin has been a major petroleum-producing province for more than a century. While the basin's oil has been the focus of a number of studies the region's gas has been largely understudied. This study examines 31 gas samples from 14 fields with the primary purpose of determining their mode(s) of formation and the role that microbial activity has had in their formation and alteration. The basin's natural gas accumulations display significant differences in both molecular and isotopic composition. Gas wetness ranges from less than 1% at Absheron to greater than 12% at Guneshli. Methane carbon isotopic composition ranges from-57 to-37[per mille sign] relative to the PDB standard. The stable carbon isotopic composition of the wet gas (C sub(2+)) components also displays a very broad range (e.g. C sub(2) ranges from-37 to- 20[per mille sign]; C sub(3) ranges from-31 to-10[per mille sign]; and nC sub(4) ranges from-30 to-11[per mille sign]). No strong depth-related trends were observed in any of the geochemical attributes. The absence of a trend implies that the gases have not been generated in situ but have migrated vertically, been altered, or represent a mixed product. Mixing is also suggested by the differences in the calculated thermal maturity levels between the C sub(2+) components and methane. In some accumulations (e.g. Karabagly) as much as 55% of the methane may have a biogenic origin. These data further indicate that among the gas samples studied those from Bakhar appear to be the most mature, with thermal maturity values consistent with the 'condensate-window'. In several fields, including Guneshli and Neftchala, the wet gas components display evidence for microbial alteration. This is largely manifested in anomalously heavy isotopic compositions of propane, n-butane, and n-pentane.
    Keywords: Biogenic Gas ; Thermal Maturity ; South Caspian Basin ; Stable Carbon Isotopes ; Engineering ; Geology
    ISSN: 0264-8172
    E-ISSN: 1873-4073
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