Genetic types and sources of natural gas in deep water areas in South Gabon Sub-basin

doi:10.3969/j.issn.1672-7703.2017.02.008

Abstract

Abstract: The natural gas in the deepwater L Gasfeld in the South Gabon Sub-basin is characterized by abnormally heavy carbon isotopic compositions, with δ¹³C₁ and δ¹³C₂ ranging from -32.8‰ to -28.4‰ and from -25.8‰ to -23.4‰, respectively. According to the ethane carbon isotope criterion of natural gas, the natural gas in the L gasfeld is classifed as coal-type gas. The investigation on regional source rocks and hydrocarbon resources shows that this area is geologically unqualifed for the formation of large coal-type gas felds, since sapropel type oil source rocks are mainly developed while humic gas source rocks are poorly developed. Carbon isotope analysis reveals that abnormally heavy carbon isotopic composition occurs during the Cretaceous Barremian Stage in the Gabon Basin and its neighboring areas, especially in the Melania Formation lacustrine good source rocks. This is similar with abnormally heavy ethane carbon isotope of natural gas in the L gasfeld. Gas source analysis indicates that the natural gas in the L gasfeld is mainly derived from high-over maturity oil cracked gas which is generated by the Cretaceous sub-salt lacustrine source rocks. In particular, the lacustrine source rocks of Barremian Melania Formation are dominant.

Key words: genetic type of natural gas, gas source analysis, South Gabon Sub-basin, carbon isotope

CLC Number:

TE112.111

Lan Lei, Sun Yumei, Wang Ke. Genetic types and sources of natural gas in deep water areas in South Gabon Sub-basin[J]. China Petroleum Exploration, 2017, 22(2): 67-73.

References

[1] 戴金星.天然气碳氢同位素特征和各类天然气鉴别[J]．天然气地球科学，1993,4(2-3):1-40. Dai Jinxing. Character of carbon and hydrogen isotope of natural gas and their identification [J]. Natural Gas and Geoscience, 1993,4(2-3):1-40.
[2] 徐永昌.天然气成因理论及应用[M].北京:科学出版社，1994:97-106. Xu Yongchang. Formation and application of natural gas [M]. Beijing: Science Press, 1994:97-106.
[3] 秦雁群，梁英波，张光亚，巴丹，杨丽丽，吴鹏. 巴西东部海域深水盐上碎屑岩油气成藏条件与勘探方向[J].中国石油勘探，2015, 20(5):63-72. Qin Yanqun, Liang Yingbo, Zhang Guangya, Ba Dan, Yang Lili, Wu Peng. Hydrocarbon accumulation conditions and further exploration of post-salt clastic rock in Brazil’s eastern deepwater area [J]. China Petroleum Exploration, 2015,20(5):63-72.
[4] Burwood R, Leplat P, Mycke B, Paulet J. Rifted margin source rock deposition: a carbon isotope and biomarker study of a West African lower cretaceous “Lacustrine” section [J]. Organic Geochemistry, 1992,19(1-3):41-52.
[5] Gon?alves F T T. Organic and isotope geochemistry of the Early Cretaceous rift sequence in the Camamu Basin, Brazil: paleolimnological inferences and source rock models [J]. Organic Geochemistry, 2002,33(1):67-80.
[6] Harris N B, Freeman K H, Pancost R D, White TS, Mitchell G D. The character and origin of lacustrine source rocks in the Lower Cretaceous synrift section, Congo Basin, west Africa [J]. AAPG Bulletin, 2004,88(8):1163-1184.
[7] 黄兴文，胡孝林，于水，孙鹏超，刘新颖．南加蓬次盆盐下油气分布规律与成藏特征[J]．中国海上油气，2015,27(2):17-23． Huang Xingwen， Hu Xiaolin, Yu Shui, Sun Pengchao, Liu Xinying. Hydrocarbon distribution and accumulation characteristics of pre-salt zones in South Gabon sub-basin [J]. China Offshore Oil and Gas, 2015,27(2):17-23．
[8] 郭念发，刘子煊.加蓬海岸盆地Salsich区块油气藏特征及勘探潜力[J].中国石油勘探，2015,20(2):82-90. Guo Nianfa，Liu Zixuan .Characteristics and exploration potential of oil and gas reservoir in Salsich Block, North Gabon Sub-basin [J].China Petroleum Exploration, 2015,20(2):82-90.
[9] 童晓光，关增淼．世界石油勘探开发图集（非洲地区分册）[M]．北京:石油工业出版社，2002． Tong Xiaoguang，Guan Zengmiao．Atlas of world petroleum exploration and development (Africa) [M]．Beijing: Petroleum Industry Press，2002．
[10] Chen Anqing，Jin Chong，Lou Zhanghua，Chen Hongde, Xu Shenglin, Huang Keke, et al． Salt tectonics and basin evolution in the Gabon Coastal basin，West Africa [J]．Journal of Earth Science，2013,24(6):903-917．
[11] Mounguengui M M, Lang J, Guiraud M, Jocktane O. Sedimentary dynamics and structural geology of pre-rift deposits of the interior basin of Gabon [J]. Journal of African Earth Sciences, 2002,35(2):315-329.
[12] 徐睿，奥立德.北加蓬次盆白垩系盐构造发育特征及成因分析[J].中国石油勘探，2016,21(5):70-74. Xu Rui, Ao Lide. Genesis and distribution of Cretaceous salt structures in North Gabon Subbasin [J]. China Petroleum Exploration, 2016,21(5):70-74.
[13] Brumboiu A O, Hawker D P, Norquay D A, Wolcott D K. Application of Semipermeable Membrane Technology in the Measurement of Hydrocarbon Gases in Drilling Fluids [M].California: Society of Petroleum Engineers, 2000.
[14] 孙玉梅，李友川，黄正吉．部分近海湖相烃源岩有机质异常碳同位素组成[J]．石油勘探与开发，2009,36(5):607-616. Sun Yumei, Li Youchuan, Huang Zhengji. Abnormal carbon isotopic compositions in organic matter of lacustrine source rocks close to sea [J]. Petroleum Exploration and Development, 2009,36(5):607-616.
[15] 黄第藩.陆相烃源岩有机质中碳同位素组成的分布特征[J].中国海上油气：地质，1993,7(4):1-5. Huang Difan. Distribution characteristics of carbon isotopic composition in organic matter in terrestrial source rocks [J]. China Offshore Oil and Gas (Geology), 1993,7(4):1-5.
[16] Schoell M. Stable isotopes in petroleum research [J]. Advances in Petroleum Geochemistry, 1984(1):215-245.
[17] 宋岩，徐永昌．天然气成因类型及其鉴别[J]．石油勘探与开发，2005,32(4):24-29． Song Yan, Xu Yongchang. Origin and identification of natural gases [J]. Petroleum Exploration and Development, 2005,32(4):24-29.
[18] 孙玉梅，孙涛，许志刚．东非海岸坦桑尼亚盆地烃源岩特征与油气来源[J]．中国海上油气，2016,28(1):1-7. Sun Yumei, Sun Tao, Xu Zhigang. Source rock characteristics and oil-gas origins in Tanzania basin, East Africa coast [J]. China Offshore Oil and Gas, 2016,28(1):1-7.