{"title":"北达科他州威利斯顿盆地泥盆纪-密西西比时期巴肯岩层的有机岩石学和地球化学","authors":"Zain Abdi, Susan M. Rimmer","doi":"10.1016/j.coal.2023.104420","DOIUrl":null,"url":null,"abstract":"<div><p><span>The Devonian–Mississippian (D–M) black shales<span> of the Bakken Formation are of interest as a hydrocarbon source due to their high total organic carbon<span> (TOC; 2.2–17.4%) content. The Upper and Lower Members of the Bakken Fm. are shallow marine (100–150 m) sequences. Thirty samples were selected for maceral identification, kerogen typing, and solid bitumen reflectance (SBR</span></span></span><sub>o</sub><span><span><span>) based on TOC content and down-core spacing. The shales contain alginite, bituminite, abundant solid bitumen (SB), and minor amounts of </span>inertinite. Solid bitumen increases in quantity with increasing </span>thermal maturity<span>. Pyrolysis (85 samples) provided S1 (avg. 8.0 mg HC/g rock), S2 (avg. 24.3 mg HC/g rock), hydrogen index (HI; avg. 201 mg HC/g TOC), oxygen index (OI; avg. 7 mg CO</span></span><sub>2</sub>/g TOC), and R<sub>o</sub> (0.60–1.03%) calculated from T<sub>max</sub>. Plots of HI vs. OI and HI vs. T<sub>max</sub> (°C) were used to assess kerogen type but are not consistently in agreement with the petrographic assessment. Some samples from more thermally mature cores plot as Type III (vitrinite) kerogen instead of Type II (alginite and bituminite) kerogen, the latter confirmed through petrographic observations of lower maturation samples. This is largely due to increased SB in more thermally mature samples (R<sub>o</sub> = 0.83–1.03%), as SB is known to have a lower HI content than Type II kerogen. Petrographic data show more alginite and bituminite (19–55%) in the thermally less mature samples (R<sub>o</sub> = 0.60–0.83%) compared to more dispersed SB (67–86%) and less alginite and bituminite (<1%) in the more thermally mature samples (R<sub>o</sub> = 0.89–1.01%).</p><p><span>Early research on the Bakken Fm. reported lower than expected vitrinite reflectance<span> values and attributed them to vitrinite “suppression”. The scarcity of vitrinite and abundance of SB suggest that early work likely reported reflectance on SB. Recent attempts to assess the thermal maturity of the Bakken black shales have converted SBR</span></span><sub>o</sub> to vitrinite reflectance equivalence (V<sub>RE</sub>). However, there are multiple SB populations present in these shales and it is not always clear which SB populations were included, possibly contributing to error. In the current study, only smooth, homogenous SB was measured (0.68–1.14% SBR<sub>o</sub>) and V<sub>RE</sub><span> values calculated (0.54–1.49%) to assess thermal maturity from the basin margin to the depocenter<span>; inclusion of measurements on granular, heterogeneous SB (14–21 vol%), which are ∼53% lower than those for smooth, homogenous SB (3–12 vol%), results in lower mean reflectances, especially in more mature samples. Vitrinite reflectance equivalent data calculated using the D–M New Albany Shale equation of Liu et al. (2019) agrees with liptinite fluorescence and Rock-Eval R</span></span><sub>o</sub>, whereas V<sub>RE</sub> based on the D–M Woodford Shale equation of Cardott and Comer (2021) does not. This suggests the importance of applying V<sub>RE</sub> equations from similar formations both in terms of thermal history, as well as kerogen type and age. Results from SBR<sub>o</sub>, Rock-Eval R<sub>o</sub>, V<sub>RE</sub><span>, and observations of alginite fluorescence indicate that samples from the current study range from the early oil window into the condensate, wet gas zone.</span></p></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":null,"pages":null},"PeriodicalIF":5.6000,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Organic petrology and geochemistry of the Devonian-Mississippian bakken formation, Williston Basin, North Dakota\",\"authors\":\"Zain Abdi, Susan M. Rimmer\",\"doi\":\"10.1016/j.coal.2023.104420\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p><span>The Devonian–Mississippian (D–M) black shales<span> of the Bakken Formation are of interest as a hydrocarbon source due to their high total organic carbon<span> (TOC; 2.2–17.4%) content. The Upper and Lower Members of the Bakken Fm. are shallow marine (100–150 m) sequences. Thirty samples were selected for maceral identification, kerogen typing, and solid bitumen reflectance (SBR</span></span></span><sub>o</sub><span><span><span>) based on TOC content and down-core spacing. The shales contain alginite, bituminite, abundant solid bitumen (SB), and minor amounts of </span>inertinite. Solid bitumen increases in quantity with increasing </span>thermal maturity<span>. Pyrolysis (85 samples) provided S1 (avg. 8.0 mg HC/g rock), S2 (avg. 24.3 mg HC/g rock), hydrogen index (HI; avg. 201 mg HC/g TOC), oxygen index (OI; avg. 7 mg CO</span></span><sub>2</sub>/g TOC), and R<sub>o</sub> (0.60–1.03%) calculated from T<sub>max</sub>. Plots of HI vs. OI and HI vs. T<sub>max</sub> (°C) were used to assess kerogen type but are not consistently in agreement with the petrographic assessment. Some samples from more thermally mature cores plot as Type III (vitrinite) kerogen instead of Type II (alginite and bituminite) kerogen, the latter confirmed through petrographic observations of lower maturation samples. This is largely due to increased SB in more thermally mature samples (R<sub>o</sub> = 0.83–1.03%), as SB is known to have a lower HI content than Type II kerogen. Petrographic data show more alginite and bituminite (19–55%) in the thermally less mature samples (R<sub>o</sub> = 0.60–0.83%) compared to more dispersed SB (67–86%) and less alginite and bituminite (<1%) in the more thermally mature samples (R<sub>o</sub> = 0.89–1.01%).</p><p><span>Early research on the Bakken Fm. reported lower than expected vitrinite reflectance<span> values and attributed them to vitrinite “suppression”. The scarcity of vitrinite and abundance of SB suggest that early work likely reported reflectance on SB. Recent attempts to assess the thermal maturity of the Bakken black shales have converted SBR</span></span><sub>o</sub> to vitrinite reflectance equivalence (V<sub>RE</sub>). However, there are multiple SB populations present in these shales and it is not always clear which SB populations were included, possibly contributing to error. In the current study, only smooth, homogenous SB was measured (0.68–1.14% SBR<sub>o</sub>) and V<sub>RE</sub><span> values calculated (0.54–1.49%) to assess thermal maturity from the basin margin to the depocenter<span>; inclusion of measurements on granular, heterogeneous SB (14–21 vol%), which are ∼53% lower than those for smooth, homogenous SB (3–12 vol%), results in lower mean reflectances, especially in more mature samples. Vitrinite reflectance equivalent data calculated using the D–M New Albany Shale equation of Liu et al. (2019) agrees with liptinite fluorescence and Rock-Eval R</span></span><sub>o</sub>, whereas V<sub>RE</sub> based on the D–M Woodford Shale equation of Cardott and Comer (2021) does not. This suggests the importance of applying V<sub>RE</sub> equations from similar formations both in terms of thermal history, as well as kerogen type and age. Results from SBR<sub>o</sub>, Rock-Eval R<sub>o</sub>, V<sub>RE</sub><span>, and observations of alginite fluorescence indicate that samples from the current study range from the early oil window into the condensate, wet gas zone.</span></p></div>\",\"PeriodicalId\":13864,\"journal\":{\"name\":\"International Journal of Coal Geology\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":5.6000,\"publicationDate\":\"2023-12-13\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"International Journal of Coal Geology\",\"FirstCategoryId\":\"5\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0166516223002380\",\"RegionNum\":2,\"RegionCategory\":\"工程技术\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"ENERGY & FUELS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"International Journal of Coal Geology","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0166516223002380","RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ENERGY & FUELS","Score":null,"Total":0}
Organic petrology and geochemistry of the Devonian-Mississippian bakken formation, Williston Basin, North Dakota
The Devonian–Mississippian (D–M) black shales of the Bakken Formation are of interest as a hydrocarbon source due to their high total organic carbon (TOC; 2.2–17.4%) content. The Upper and Lower Members of the Bakken Fm. are shallow marine (100–150 m) sequences. Thirty samples were selected for maceral identification, kerogen typing, and solid bitumen reflectance (SBRo) based on TOC content and down-core spacing. The shales contain alginite, bituminite, abundant solid bitumen (SB), and minor amounts of inertinite. Solid bitumen increases in quantity with increasing thermal maturity. Pyrolysis (85 samples) provided S1 (avg. 8.0 mg HC/g rock), S2 (avg. 24.3 mg HC/g rock), hydrogen index (HI; avg. 201 mg HC/g TOC), oxygen index (OI; avg. 7 mg CO2/g TOC), and Ro (0.60–1.03%) calculated from Tmax. Plots of HI vs. OI and HI vs. Tmax (°C) were used to assess kerogen type but are not consistently in agreement with the petrographic assessment. Some samples from more thermally mature cores plot as Type III (vitrinite) kerogen instead of Type II (alginite and bituminite) kerogen, the latter confirmed through petrographic observations of lower maturation samples. This is largely due to increased SB in more thermally mature samples (Ro = 0.83–1.03%), as SB is known to have a lower HI content than Type II kerogen. Petrographic data show more alginite and bituminite (19–55%) in the thermally less mature samples (Ro = 0.60–0.83%) compared to more dispersed SB (67–86%) and less alginite and bituminite (<1%) in the more thermally mature samples (Ro = 0.89–1.01%).
Early research on the Bakken Fm. reported lower than expected vitrinite reflectance values and attributed them to vitrinite “suppression”. The scarcity of vitrinite and abundance of SB suggest that early work likely reported reflectance on SB. Recent attempts to assess the thermal maturity of the Bakken black shales have converted SBRo to vitrinite reflectance equivalence (VRE). However, there are multiple SB populations present in these shales and it is not always clear which SB populations were included, possibly contributing to error. In the current study, only smooth, homogenous SB was measured (0.68–1.14% SBRo) and VRE values calculated (0.54–1.49%) to assess thermal maturity from the basin margin to the depocenter; inclusion of measurements on granular, heterogeneous SB (14–21 vol%), which are ∼53% lower than those for smooth, homogenous SB (3–12 vol%), results in lower mean reflectances, especially in more mature samples. Vitrinite reflectance equivalent data calculated using the D–M New Albany Shale equation of Liu et al. (2019) agrees with liptinite fluorescence and Rock-Eval Ro, whereas VRE based on the D–M Woodford Shale equation of Cardott and Comer (2021) does not. This suggests the importance of applying VRE equations from similar formations both in terms of thermal history, as well as kerogen type and age. Results from SBRo, Rock-Eval Ro, VRE, and observations of alginite fluorescence indicate that samples from the current study range from the early oil window into the condensate, wet gas zone.
期刊介绍:
The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.