In 2013, a great breakthrough of deep petroleum exploration was achieved in the Cambrian pre-salt intervals of Wells Zhongshen1(ZS1) and Zhongshen1C(ZS1C), Tazhong Uplift. However, the hydrocarbon discovery in the Cam...In 2013, a great breakthrough of deep petroleum exploration was achieved in the Cambrian pre-salt intervals of Wells Zhongshen1(ZS1) and Zhongshen1C(ZS1C), Tazhong Uplift. However, the hydrocarbon discovery in the Cambrian pre-salt intervals has triggered extensive controversy regarding the source of marine oils in the Tarim Basin. The geochemistry and origin of the Cambrian pre-salt hydrocarbons in Wells ZS1 and ZS1 C were investigated using GC, GC-MS and stable carbon isotope technique. These hydrocarbons can be easily distinguished into two genetic families based on their geochemical and carbon isotopic compositions. The oil and natural gases from the Awatage Formation of Well ZS1 are derived from Middle-Upper Ordovician source rocks. In contrast, the condensate and gases from the Xiaoerbulake Formation of Wells ZS1 and ZS1 C probably originate from Cambrian source rocks. The recent discovery of these hydrocarbons with two different sources in Wells ZS1 and ZS1 C suggests that both Middle-Upper Ordovician-sourced hydrocarbons and Cambrian-sourced petroleums are accumulated in the Tazhong Uplift, presenting a great exploration potential.展开更多
Since the discovery of the Tahe oilfield, it has been controversial on whether the main source rock is in the Cambrian or Middle-Upper Ordovician strata. In this paper, it is assumed that the crude oil from the Wells ...Since the discovery of the Tahe oilfield, it has been controversial on whether the main source rock is in the Cambrian or Middle-Upper Ordovician strata. In this paper, it is assumed that the crude oil from the Wells YM 2 and TD 2 was derived from the Middle-Upper Ordovician and Cambrian source rocks, respectively. We analyzed the biomarkers of the crude oil, asphalt-adsorbed hydrocarbon and saturated hydrocarbon in bitumen inclusions from the Lunnan and Hade areas in the North Uplift of the Tarim Basin. Results show that the ratios of tricyclic terpane C2~/C23 in the crude oil, asphalt-adsorbed hydrocarbon and saturated hydrocarbon in bitumen inclusions are less than 1.0, indicating that they might be from Upper Ordovician source rocks; the ratios of C28/（C27＋C28＋C29） steranes in the saturated hydrocarbon from reservoir bitumen and bitumen inclusions are higher than 25, suggesting that they might come from the Cambrian source rocks, however, the ratios of C28/（C27＋C28＋C29） steranes in oil from the North Uplift are less than 25, suggesting that they might be sourced from the Upper Ordovician source rocks. These findings demonstrate that the sources of crude oil in the Tarim Basin are complicated. The chemical composition and carbon isotopes of Ordovician reservoired oil in the Tarim Basin indicated that the crude oil in the North Uplift （including the Tahe oilfield） and Tazhong Depression was within mixture areas of crude oil from the Wells YM 2 and TD 2 as the end members of the Cambrian and Middle-Upper Ordovician sourced oils, respectively. This observation suggests that the crude oil in the Ordovician strata is a mixture of oils from the Cambrian and Ordovician source rocks, with increasing contribution from the Cambrian source rocks from the southern slope of the North Uplift to northern slope of the Central Uplift of the Tarim Basin. Considering the lithology and sedimentary facies data, the spatial distribution of the Cambrian, Middle-Lower Ordovician and Upper Ordovician source rocks was reconstructed on the basis of seismic reflection characteristics, and high-quality source rocks were revealed to be mainly located in the slope belt of the basin and were longitudinally developed over the maximum flooding surface during the progressive-regressive cycle. Affected by the transformation of the tectonic framework in the basin, the overlays of source rocks in different regions are different and the distribution of oil and gas was determined by the initial basin sedimentary structure and later reformation process. The northern slope of the Central Uplift-Shuntuo-Gucheng areas would be a recent important target for oil and gas exploration, since they have been near the slope area for a long time.展开更多
Patterns of septal insertion were analyzed in three species of Agetolites from the Upper Ordovician in Yushan County, Jiangxi Province of China. Agetolites is a peculiar coral possessing features of both tabulate （e....Patterns of septal insertion were analyzed in three species of Agetolites from the Upper Ordovician in Yushan County, Jiangxi Province of China. Agetolites is a peculiar coral possessing features of both tabulate （e.g., mural pores） and rugose corals （e.g., welldeveloped septa）. Septal patterns have long been considered to be indicative of the origin of corals, and the pattern of septal insertion in Agetolites has been known to be typical of rugosans. This study, however, reveals that the patterns in Ageto lites are rather random and cannot be an indication of its rugosan affinity. It is suggested that Agetolites probably has a closer phylogenetic relation with tabulates than with either rugosans or scleractinians. Two insertion patterns of the first six septa were detected （Types I and II）. Type I is interpreted as scleractinian pattern whereas Type II as typical pattern of rugosans. Types 1 and 2 are septal patterns of the second stage recognized in this study. Type 1 insertion occurs in six sectors located in the center of each interseptal space, suggesting scleractinian pattern of insertion. Type 2 insertion occurs in four sectors that are comparable with alar and counter sectors in rugose corals. Four patterns of the third （Types AD） and fourth stages （Types ad） of septal insertion have also been recognized in Agetolites. Type A only occurs in two adjacent sectors possibly due to the in completeness of septal development. Type B presents rugosan pattern. Types C and D resemble scleractinian pattern in most aspects. Types a, b, and c present no clear attribution to rugosan or scleractinian pattern probably due to the incompleteness of septal development whereas Type d is observable in rugose corals.展开更多
基金supported by the Science Foundation of China University of Petroleum,Beijing(Grant No.2462015YQ0101)
文摘In 2013, a great breakthrough of deep petroleum exploration was achieved in the Cambrian pre-salt intervals of Wells Zhongshen1(ZS1) and Zhongshen1C(ZS1C), Tazhong Uplift. However, the hydrocarbon discovery in the Cambrian pre-salt intervals has triggered extensive controversy regarding the source of marine oils in the Tarim Basin. The geochemistry and origin of the Cambrian pre-salt hydrocarbons in Wells ZS1 and ZS1 C were investigated using GC, GC-MS and stable carbon isotope technique. These hydrocarbons can be easily distinguished into two genetic families based on their geochemical and carbon isotopic compositions. The oil and natural gases from the Awatage Formation of Well ZS1 are derived from Middle-Upper Ordovician source rocks. In contrast, the condensate and gases from the Xiaoerbulake Formation of Wells ZS1 and ZS1 C probably originate from Cambrian source rocks. The recent discovery of these hydrocarbons with two different sources in Wells ZS1 and ZS1 C suggests that both Middle-Upper Ordovician-sourced hydrocarbons and Cambrian-sourced petroleums are accumulated in the Tazhong Uplift, presenting a great exploration potential.
基金supported by the National Natural Science Foundation of China(Grant Nos.41230312,41322016,41625009)the Key Project of China National Program for Fundamental Research and Development(Grant No. 2012CB214800)
文摘Since the discovery of the Tahe oilfield, it has been controversial on whether the main source rock is in the Cambrian or Middle-Upper Ordovician strata. In this paper, it is assumed that the crude oil from the Wells YM 2 and TD 2 was derived from the Middle-Upper Ordovician and Cambrian source rocks, respectively. We analyzed the biomarkers of the crude oil, asphalt-adsorbed hydrocarbon and saturated hydrocarbon in bitumen inclusions from the Lunnan and Hade areas in the North Uplift of the Tarim Basin. Results show that the ratios of tricyclic terpane C2~/C23 in the crude oil, asphalt-adsorbed hydrocarbon and saturated hydrocarbon in bitumen inclusions are less than 1.0, indicating that they might be from Upper Ordovician source rocks; the ratios of C28/（C27＋C28＋C29） steranes in the saturated hydrocarbon from reservoir bitumen and bitumen inclusions are higher than 25, suggesting that they might come from the Cambrian source rocks, however, the ratios of C28/（C27＋C28＋C29） steranes in oil from the North Uplift are less than 25, suggesting that they might be sourced from the Upper Ordovician source rocks. These findings demonstrate that the sources of crude oil in the Tarim Basin are complicated. The chemical composition and carbon isotopes of Ordovician reservoired oil in the Tarim Basin indicated that the crude oil in the North Uplift （including the Tahe oilfield） and Tazhong Depression was within mixture areas of crude oil from the Wells YM 2 and TD 2 as the end members of the Cambrian and Middle-Upper Ordovician sourced oils, respectively. This observation suggests that the crude oil in the Ordovician strata is a mixture of oils from the Cambrian and Ordovician source rocks, with increasing contribution from the Cambrian source rocks from the southern slope of the North Uplift to northern slope of the Central Uplift of the Tarim Basin. Considering the lithology and sedimentary facies data, the spatial distribution of the Cambrian, Middle-Lower Ordovician and Upper Ordovician source rocks was reconstructed on the basis of seismic reflection characteristics, and high-quality source rocks were revealed to be mainly located in the slope belt of the basin and were longitudinally developed over the maximum flooding surface during the progressive-regressive cycle. Affected by the transformation of the tectonic framework in the basin, the overlays of source rocks in different regions are different and the distribution of oil and gas was determined by the initial basin sedimentary structure and later reformation process. The northern slope of the Central Uplift-Shuntuo-Gucheng areas would be a recent important target for oil and gas exploration, since they have been near the slope area for a long time.
基金supported by the Invitation and Training of Outstanding Overseas Student Researcher Program by Korea Science and Engineering Foundation(Grant No.KOSEF 211-2007-1-C00047)Korea Research Foundation funded by the Korean Government(MOEHRD)to DJL(Grant No.KRF-2006-312-C00690)
文摘Patterns of septal insertion were analyzed in three species of Agetolites from the Upper Ordovician in Yushan County, Jiangxi Province of China. Agetolites is a peculiar coral possessing features of both tabulate （e.g., mural pores） and rugose corals （e.g., welldeveloped septa）. Septal patterns have long been considered to be indicative of the origin of corals, and the pattern of septal insertion in Agetolites has been known to be typical of rugosans. This study, however, reveals that the patterns in Ageto lites are rather random and cannot be an indication of its rugosan affinity. It is suggested that Agetolites probably has a closer phylogenetic relation with tabulates than with either rugosans or scleractinians. Two insertion patterns of the first six septa were detected （Types I and II）. Type I is interpreted as scleractinian pattern whereas Type II as typical pattern of rugosans. Types 1 and 2 are septal patterns of the second stage recognized in this study. Type 1 insertion occurs in six sectors located in the center of each interseptal space, suggesting scleractinian pattern of insertion. Type 2 insertion occurs in four sectors that are comparable with alar and counter sectors in rugose corals. Four patterns of the third （Types AD） and fourth stages （Types ad） of septal insertion have also been recognized in Agetolites. Type A only occurs in two adjacent sectors possibly due to the in completeness of septal development. Type B presents rugosan pattern. Types C and D resemble scleractinian pattern in most aspects. Types a, b, and c present no clear attribution to rugosan or scleractinian pattern probably due to the incompleteness of septal development whereas Type d is observable in rugose corals.
