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Heather Lareau - One of the best experts on this subject based on the ideXlab platform.

  • bitumen geochemistry and producibility in the upper cretaceous Niobrara formation Shale oil play
    AAPG Bulletin, 2021
    Co-Authors: Yuanjia Han Brian Horsfield Nicolaj Mahlstedt, Heather Lareau
    Abstract:

    In the Upper Cretaceous Niobrara Formation Shale oil play, considerable oil fractions are produced directly from C14+ bitumen-in-place, e.g., extractable organic matter (EOM). This report provides new insights on the geochemistry and producibility of C14+ bitumen by integrating the full process of generation, retention, conversion, expulsion, and production, as a whole, in the Niobrara Shale oil system. Hydrocarbons are found not to be generated primarily from kerogen, but rather from the secondary conversion of polar compounds. Maturation is essentially the underlying driving force that determines the geochemistry of C14+ bitumen in source rocks. However, the in-situ cracking of C14+ bitumen does not occur in chalk reservoirs at the maturity stage investigated (430–465 °C TmaxE). Instead of maturation, the geochemistry of C14+ bitumen present in reservoirs is principally determined by migration and associated fractionation. The intraformational migration has fractionated the generated oil into a higher saturated fluid and, therefore, C14+ bitumen accumulated in chalk reservoirs is more producible than that retained in source rocks. In comparison, the bulk fractionation effect associated with production is not as pronounced as that of expulsion. Therefore, the bulk compositions of chalk bitumen strongly resemble those of crude oils. Among the least mobile nitrogen-, sulfur-, and oxygen- containing (NSO) compounds, N1 species are nevertheless partitioned into crude oils during production, and the molecular weight exhibits a less apparent effect on their producibility than chemical affinity, i.e., aromaticity and aliphaticity. Accordingly, a relative enrichment of C5+ heavier carbazoles into crude oils rather than the lighter C1-5 carbazoles was documented.

  • factors controlling source and reservoir characteristics in the Niobrara Shale oil system denver basin
    AAPG Bulletin, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, David J Curry, Richard Wirth, Heather Lareau
    Abstract:

    This paper clarifies the controls of oil retention in the Niobrara Formation, Denver Basin, in the western United States. Sweet spots have been recognized using a total of 98 core samples from 5 wells with maturities covering the oil window. Oil retention in the source rock samples (carbonate content 30 wt. %) is controlled by carbonate content, which is positively related to the amount of retained oil. Petrographic features indicate that oil or bitumen is stored in porous calcite fossils (i.e., coccolith and foraminifera), which provide additional space for petroleum storage. Chalk samples (carbonate >85 wt. %) are characterized by anomalously low Tmax values caused by the influence of heavy petroleum or bitumen. The amount of this bitumen is higher than the initial petroleum potential of kerogen in A and B chalks and thus must have been emplaced here. The most likely sources are juxtaposed organic-rich marl layers. Thus, sweet spots occur where carbonate content is either low (high TOC) or high (low TOC), whereas production of petroleum from the pore space of presumably brittle chalk seems more attractive than production from organic- and clay-rich rocks.

  • intraformational migration of petroleum insights into the development of sweet spot in the cretaceous Niobrara Shale oil system denver basin
    Marine and Petroleum Geology, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Heather Lareau, Nicolaj Mahlstedt
    Abstract:

    Abstract The Cretaceous Niobrara Formation is one of the latest unconventional exploration targets in North America. In this paper, an overall Type-II marine organofacies with some variability is present within a core which consists of alternating marls and chalks, covering a maturity range of 0.8–1.0 %Rc (calculated vitrinite reflectance). Enhanced oil saturation index (OSI) values have previously been reported for the chalk, and here a positive trend (R2 = 0.92) between the OSI and the percentage of saturates in gross fractions is present. Thus, the saturate fraction gradually increases from 40% to above 60% as the OSI increases from 40 to 550 mg HC/g TOC (total organic carbon). Extremely high OSI values (>300 mg HC/g TOC) are characteristic of Niobrara chalks. Therefore, the chalk intervals represent primary sweet spots. Using a combined analytical approach, petroleum has been shown to migrate from the organic-rich marls into juxtaposed chalks, and that this has fractionated oils into higher quality liquids. Extractable organic matter in the chalks is clearly enriched in saturate hydrocarbons, while the NSO-containing polar compounds are preferentially retained in the Shale and marl units. Compared with the significant fractionation effects between these gross fractions, fractionation within a given compound class is nevertheless indistinct.

  • compositional fractionation of petroleum from reservoir to wellhead in the Niobrara Shale oil play
    International Journal of Coal Geology, 2018
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, Heather Lareau, David J Curry
    Abstract:

    Abstract Hydraulic fracturing is routinely used to stimulate unconventional reservoirs. In the Niobrara Shale oil play there are several fracking targets, but the actual stimulated rock volume is not well constrained. This means that allocating produced oil to specific reservoirs, in essence oil-reservoir correlation, is not straightforward. The data presented here support that the chalk units are the principal production zones in the Niobrara Shale oil play. Several lines of evidence, such as the presence of heavy-end n-alkanes (> n-C31), consistence in composition of gross fractions, the distribution of C27-28-29 diasteranes, as well as the pristane to phytane ratio, all suggest that oils were produced from the A- & B- chalks, particularly from the A-Chalk. During production, a selective partitioning of lighter hydrocarbons into the migrating fluids could nevertheless occur, in particular as regards the n-alkanes domain and their carbon isotopic compositions. Regarding the latter, a depletion of 13C in the produced oil's n-alkanes by more than three per mil relative to all of those core extracts was observed. This finding suggests that compound specific isotope analysis in both oil-reservoir and oil-source rock correlations cannot be taken at face value, i.e. by simple matching of values. Besides that, fractionation appears to result in the enrichment of rather aliphatic nitrogen-containing compounds in crude oils.

Yuanjia Han - One of the best experts on this subject based on the ideXlab platform.

  • factors controlling source and reservoir characteristics in the Niobrara Shale oil system denver basin
    AAPG Bulletin, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, David J Curry, Richard Wirth, Heather Lareau
    Abstract:

    This paper clarifies the controls of oil retention in the Niobrara Formation, Denver Basin, in the western United States. Sweet spots have been recognized using a total of 98 core samples from 5 wells with maturities covering the oil window. Oil retention in the source rock samples (carbonate content 30 wt. %) is controlled by carbonate content, which is positively related to the amount of retained oil. Petrographic features indicate that oil or bitumen is stored in porous calcite fossils (i.e., coccolith and foraminifera), which provide additional space for petroleum storage. Chalk samples (carbonate >85 wt. %) are characterized by anomalously low Tmax values caused by the influence of heavy petroleum or bitumen. The amount of this bitumen is higher than the initial petroleum potential of kerogen in A and B chalks and thus must have been emplaced here. The most likely sources are juxtaposed organic-rich marl layers. Thus, sweet spots occur where carbonate content is either low (high TOC) or high (low TOC), whereas production of petroleum from the pore space of presumably brittle chalk seems more attractive than production from organic- and clay-rich rocks.

  • intraformational migration of petroleum insights into the development of sweet spot in the cretaceous Niobrara Shale oil system denver basin
    Marine and Petroleum Geology, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Heather Lareau, Nicolaj Mahlstedt
    Abstract:

    Abstract The Cretaceous Niobrara Formation is one of the latest unconventional exploration targets in North America. In this paper, an overall Type-II marine organofacies with some variability is present within a core which consists of alternating marls and chalks, covering a maturity range of 0.8–1.0 %Rc (calculated vitrinite reflectance). Enhanced oil saturation index (OSI) values have previously been reported for the chalk, and here a positive trend (R2 = 0.92) between the OSI and the percentage of saturates in gross fractions is present. Thus, the saturate fraction gradually increases from 40% to above 60% as the OSI increases from 40 to 550 mg HC/g TOC (total organic carbon). Extremely high OSI values (>300 mg HC/g TOC) are characteristic of Niobrara chalks. Therefore, the chalk intervals represent primary sweet spots. Using a combined analytical approach, petroleum has been shown to migrate from the organic-rich marls into juxtaposed chalks, and that this has fractionated oils into higher quality liquids. Extractable organic matter in the chalks is clearly enriched in saturate hydrocarbons, while the NSO-containing polar compounds are preferentially retained in the Shale and marl units. Compared with the significant fractionation effects between these gross fractions, fractionation within a given compound class is nevertheless indistinct.

  • compositional fractionation of petroleum from reservoir to wellhead in the Niobrara Shale oil play
    International Journal of Coal Geology, 2018
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, Heather Lareau, David J Curry
    Abstract:

    Abstract Hydraulic fracturing is routinely used to stimulate unconventional reservoirs. In the Niobrara Shale oil play there are several fracking targets, but the actual stimulated rock volume is not well constrained. This means that allocating produced oil to specific reservoirs, in essence oil-reservoir correlation, is not straightforward. The data presented here support that the chalk units are the principal production zones in the Niobrara Shale oil play. Several lines of evidence, such as the presence of heavy-end n-alkanes (> n-C31), consistence in composition of gross fractions, the distribution of C27-28-29 diasteranes, as well as the pristane to phytane ratio, all suggest that oils were produced from the A- & B- chalks, particularly from the A-Chalk. During production, a selective partitioning of lighter hydrocarbons into the migrating fluids could nevertheless occur, in particular as regards the n-alkanes domain and their carbon isotopic compositions. Regarding the latter, a depletion of 13C in the produced oil's n-alkanes by more than three per mil relative to all of those core extracts was observed. This finding suggests that compound specific isotope analysis in both oil-reservoir and oil-source rock correlations cannot be taken at face value, i.e. by simple matching of values. Besides that, fractionation appears to result in the enrichment of rather aliphatic nitrogen-containing compounds in crude oils.

Nicolaj Mahlstedt - One of the best experts on this subject based on the ideXlab platform.

  • factors controlling source and reservoir characteristics in the Niobrara Shale oil system denver basin
    AAPG Bulletin, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, David J Curry, Richard Wirth, Heather Lareau
    Abstract:

    This paper clarifies the controls of oil retention in the Niobrara Formation, Denver Basin, in the western United States. Sweet spots have been recognized using a total of 98 core samples from 5 wells with maturities covering the oil window. Oil retention in the source rock samples (carbonate content 30 wt. %) is controlled by carbonate content, which is positively related to the amount of retained oil. Petrographic features indicate that oil or bitumen is stored in porous calcite fossils (i.e., coccolith and foraminifera), which provide additional space for petroleum storage. Chalk samples (carbonate >85 wt. %) are characterized by anomalously low Tmax values caused by the influence of heavy petroleum or bitumen. The amount of this bitumen is higher than the initial petroleum potential of kerogen in A and B chalks and thus must have been emplaced here. The most likely sources are juxtaposed organic-rich marl layers. Thus, sweet spots occur where carbonate content is either low (high TOC) or high (low TOC), whereas production of petroleum from the pore space of presumably brittle chalk seems more attractive than production from organic- and clay-rich rocks.

  • intraformational migration of petroleum insights into the development of sweet spot in the cretaceous Niobrara Shale oil system denver basin
    Marine and Petroleum Geology, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Heather Lareau, Nicolaj Mahlstedt
    Abstract:

    Abstract The Cretaceous Niobrara Formation is one of the latest unconventional exploration targets in North America. In this paper, an overall Type-II marine organofacies with some variability is present within a core which consists of alternating marls and chalks, covering a maturity range of 0.8–1.0 %Rc (calculated vitrinite reflectance). Enhanced oil saturation index (OSI) values have previously been reported for the chalk, and here a positive trend (R2 = 0.92) between the OSI and the percentage of saturates in gross fractions is present. Thus, the saturate fraction gradually increases from 40% to above 60% as the OSI increases from 40 to 550 mg HC/g TOC (total organic carbon). Extremely high OSI values (>300 mg HC/g TOC) are characteristic of Niobrara chalks. Therefore, the chalk intervals represent primary sweet spots. Using a combined analytical approach, petroleum has been shown to migrate from the organic-rich marls into juxtaposed chalks, and that this has fractionated oils into higher quality liquids. Extractable organic matter in the chalks is clearly enriched in saturate hydrocarbons, while the NSO-containing polar compounds are preferentially retained in the Shale and marl units. Compared with the significant fractionation effects between these gross fractions, fractionation within a given compound class is nevertheless indistinct.

  • compositional fractionation of petroleum from reservoir to wellhead in the Niobrara Shale oil play
    International Journal of Coal Geology, 2018
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, Heather Lareau, David J Curry
    Abstract:

    Abstract Hydraulic fracturing is routinely used to stimulate unconventional reservoirs. In the Niobrara Shale oil play there are several fracking targets, but the actual stimulated rock volume is not well constrained. This means that allocating produced oil to specific reservoirs, in essence oil-reservoir correlation, is not straightforward. The data presented here support that the chalk units are the principal production zones in the Niobrara Shale oil play. Several lines of evidence, such as the presence of heavy-end n-alkanes (> n-C31), consistence in composition of gross fractions, the distribution of C27-28-29 diasteranes, as well as the pristane to phytane ratio, all suggest that oils were produced from the A- & B- chalks, particularly from the A-Chalk. During production, a selective partitioning of lighter hydrocarbons into the migrating fluids could nevertheless occur, in particular as regards the n-alkanes domain and their carbon isotopic compositions. Regarding the latter, a depletion of 13C in the produced oil's n-alkanes by more than three per mil relative to all of those core extracts was observed. This finding suggests that compound specific isotope analysis in both oil-reservoir and oil-source rock correlations cannot be taken at face value, i.e. by simple matching of values. Besides that, fractionation appears to result in the enrichment of rather aliphatic nitrogen-containing compounds in crude oils.

Brian Horsfield - One of the best experts on this subject based on the ideXlab platform.

  • factors controlling source and reservoir characteristics in the Niobrara Shale oil system denver basin
    AAPG Bulletin, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, David J Curry, Richard Wirth, Heather Lareau
    Abstract:

    This paper clarifies the controls of oil retention in the Niobrara Formation, Denver Basin, in the western United States. Sweet spots have been recognized using a total of 98 core samples from 5 wells with maturities covering the oil window. Oil retention in the source rock samples (carbonate content 30 wt. %) is controlled by carbonate content, which is positively related to the amount of retained oil. Petrographic features indicate that oil or bitumen is stored in porous calcite fossils (i.e., coccolith and foraminifera), which provide additional space for petroleum storage. Chalk samples (carbonate >85 wt. %) are characterized by anomalously low Tmax values caused by the influence of heavy petroleum or bitumen. The amount of this bitumen is higher than the initial petroleum potential of kerogen in A and B chalks and thus must have been emplaced here. The most likely sources are juxtaposed organic-rich marl layers. Thus, sweet spots occur where carbonate content is either low (high TOC) or high (low TOC), whereas production of petroleum from the pore space of presumably brittle chalk seems more attractive than production from organic- and clay-rich rocks.

  • intraformational migration of petroleum insights into the development of sweet spot in the cretaceous Niobrara Shale oil system denver basin
    Marine and Petroleum Geology, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Heather Lareau, Nicolaj Mahlstedt
    Abstract:

    Abstract The Cretaceous Niobrara Formation is one of the latest unconventional exploration targets in North America. In this paper, an overall Type-II marine organofacies with some variability is present within a core which consists of alternating marls and chalks, covering a maturity range of 0.8–1.0 %Rc (calculated vitrinite reflectance). Enhanced oil saturation index (OSI) values have previously been reported for the chalk, and here a positive trend (R2 = 0.92) between the OSI and the percentage of saturates in gross fractions is present. Thus, the saturate fraction gradually increases from 40% to above 60% as the OSI increases from 40 to 550 mg HC/g TOC (total organic carbon). Extremely high OSI values (>300 mg HC/g TOC) are characteristic of Niobrara chalks. Therefore, the chalk intervals represent primary sweet spots. Using a combined analytical approach, petroleum has been shown to migrate from the organic-rich marls into juxtaposed chalks, and that this has fractionated oils into higher quality liquids. Extractable organic matter in the chalks is clearly enriched in saturate hydrocarbons, while the NSO-containing polar compounds are preferentially retained in the Shale and marl units. Compared with the significant fractionation effects between these gross fractions, fractionation within a given compound class is nevertheless indistinct.

  • compositional fractionation of petroleum from reservoir to wellhead in the Niobrara Shale oil play
    International Journal of Coal Geology, 2018
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, Heather Lareau, David J Curry
    Abstract:

    Abstract Hydraulic fracturing is routinely used to stimulate unconventional reservoirs. In the Niobrara Shale oil play there are several fracking targets, but the actual stimulated rock volume is not well constrained. This means that allocating produced oil to specific reservoirs, in essence oil-reservoir correlation, is not straightforward. The data presented here support that the chalk units are the principal production zones in the Niobrara Shale oil play. Several lines of evidence, such as the presence of heavy-end n-alkanes (> n-C31), consistence in composition of gross fractions, the distribution of C27-28-29 diasteranes, as well as the pristane to phytane ratio, all suggest that oils were produced from the A- & B- chalks, particularly from the A-Chalk. During production, a selective partitioning of lighter hydrocarbons into the migrating fluids could nevertheless occur, in particular as regards the n-alkanes domain and their carbon isotopic compositions. Regarding the latter, a depletion of 13C in the produced oil's n-alkanes by more than three per mil relative to all of those core extracts was observed. This finding suggests that compound specific isotope analysis in both oil-reservoir and oil-source rock correlations cannot be taken at face value, i.e. by simple matching of values. Besides that, fractionation appears to result in the enrichment of rather aliphatic nitrogen-containing compounds in crude oils.

David J Curry - One of the best experts on this subject based on the ideXlab platform.

  • factors controlling source and reservoir characteristics in the Niobrara Shale oil system denver basin
    AAPG Bulletin, 2019
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, David J Curry, Richard Wirth, Heather Lareau
    Abstract:

    This paper clarifies the controls of oil retention in the Niobrara Formation, Denver Basin, in the western United States. Sweet spots have been recognized using a total of 98 core samples from 5 wells with maturities covering the oil window. Oil retention in the source rock samples (carbonate content 30 wt. %) is controlled by carbonate content, which is positively related to the amount of retained oil. Petrographic features indicate that oil or bitumen is stored in porous calcite fossils (i.e., coccolith and foraminifera), which provide additional space for petroleum storage. Chalk samples (carbonate >85 wt. %) are characterized by anomalously low Tmax values caused by the influence of heavy petroleum or bitumen. The amount of this bitumen is higher than the initial petroleum potential of kerogen in A and B chalks and thus must have been emplaced here. The most likely sources are juxtaposed organic-rich marl layers. Thus, sweet spots occur where carbonate content is either low (high TOC) or high (low TOC), whereas production of petroleum from the pore space of presumably brittle chalk seems more attractive than production from organic- and clay-rich rocks.

  • compositional fractionation of petroleum from reservoir to wellhead in the Niobrara Shale oil play
    International Journal of Coal Geology, 2018
    Co-Authors: Yuanjia Han, Brian Horsfield, Nicolaj Mahlstedt, Heather Lareau, David J Curry
    Abstract:

    Abstract Hydraulic fracturing is routinely used to stimulate unconventional reservoirs. In the Niobrara Shale oil play there are several fracking targets, but the actual stimulated rock volume is not well constrained. This means that allocating produced oil to specific reservoirs, in essence oil-reservoir correlation, is not straightforward. The data presented here support that the chalk units are the principal production zones in the Niobrara Shale oil play. Several lines of evidence, such as the presence of heavy-end n-alkanes (> n-C31), consistence in composition of gross fractions, the distribution of C27-28-29 diasteranes, as well as the pristane to phytane ratio, all suggest that oils were produced from the A- & B- chalks, particularly from the A-Chalk. During production, a selective partitioning of lighter hydrocarbons into the migrating fluids could nevertheless occur, in particular as regards the n-alkanes domain and their carbon isotopic compositions. Regarding the latter, a depletion of 13C in the produced oil's n-alkanes by more than three per mil relative to all of those core extracts was observed. This finding suggests that compound specific isotope analysis in both oil-reservoir and oil-source rock correlations cannot be taken at face value, i.e. by simple matching of values. Besides that, fractionation appears to result in the enrichment of rather aliphatic nitrogen-containing compounds in crude oils.