摘要
中国南方寒武系富有机质页岩具有很大的页岩气资源潜力,但不同地区的勘探效果差异较大。本文分析了近年来我国寒武系页岩含气性研究进展,讨论了寒武系页岩的储层特征、总有机碳(TOC)含量、孔隙度和构造保存条件等因素对页岩含气性的影响。中上扬子地区的寒武系富有机质页岩主要发育在绵阳—长宁裂陷槽、鄂西裂陷槽和湘黔渝深水陆棚—斜坡等沉积相区。寒武系页岩的孔隙度主要分布在1%~6%,孔隙以微孔和介孔占主导,总体以孤立密集发育的海绵状有机孔为主,区别于志留系龙马溪组页岩极为发育的气泡状有机孔。位于裂陷槽环境的寒武系筇竹寺组/水井沱组页岩的有机孔隙发育程度较好(有机质平均面孔率可达20%~50%),且无机孔也对总孔隙度有所贡献;页岩现今含气量为1.5~5.5 m^(3)/t,是理论总生成气量的10%~30%(最大甚至超过50%),反映页岩气保存条件总体较好。而位于深水陆棚—斜坡环境的寒武系牛蹄塘组页岩有机孔发育程度较差(有机质平均面孔率小于20%),页岩现今含气量基本小于1.0 m^(3)/t,不足理论总生成气量的10%,反映页岩气可能发生过大规模散失,页岩气保存条件较差。中上扬子地区寒武系富有机质页岩底部通常存在区域性的不整合面,在沉积之后也普遍经历过强烈的后期构造抬升作用,均可能造成油气的散失。相比之下,绵阳—长宁裂陷槽和鄂西裂陷槽环境下的寒武系页岩孔隙发育情况和构造保存条件相对较好,富有机质层段内发育的钙质页岩/泥灰岩夹层可能会限制油气在垂向上的运移和散失,为寒武系页岩气的保存创造了有利条件,应是寒武系页岩气勘探的重点目标,这也与我国目前的寒武系页岩气勘探实际相对应。
The Cambrian shale gas resource potential of southern China is expected to be enormous with its widely distributed high-maturity organic-rich shales;however,success in shale gas exploration is uneven across the region.In this paper,we analyze the current research progress in the study of Cambrian shale gas geology in southern China,and discuss the key factors that determine the shale gas content,including reservoir characteristics,total organic carbon(TOC)content,porosity as well as tectonic conditions for gas preservation.The organic-rich Cambrian shales of the middle-upper Yangtze regions are mainly distributed in the intracratonic troughs in the Mianyang Changning area and western Hubei,and in the deepwater shelf-slope area bordering Hunan,Guizhou and Chongqing.The porosity of Cambrian shales commonly ranges from 1%to 6%,and the pores are dominated by micropores and mesopores,mainly isolated,spongelike organic pores,which are very different from the widely-developed bobble-like organic pores in the Silurian Longmaxi shale.Organic pores are well developed in the Cambrian Qiongzhusi/Shuijingtuo shales of the troughs,with average organic porosity ranging between 20%50%,and inorganic pores are also abundant and contribute to the total porosity.The shale gas content ranges from 1.5 to 5.5 m^(3)/t,which is 10%30%(in some samples as high as~50%)of the estimated total gas generation,indicating favorable tectonic preservation conditions in the troughs.In contrast,organic pores are poorly developed in the Cambrian Niutitang shale of the deepwater shelf-slope area,with average organic porosity less than 20%.The shale gas content is below 1.0 m^(3)/t,or less than~10%of the estimated total gas generation,indicating poor preservation conditions and large-scale gas loss in the area.The gas loss might be caused by regional unconformities developed at the bottom of the organic-rich Cambrian shale formation as well as severe post-depositional tectonic uplift in the middle-upper Yangtze.However,interbedded carbonate-rich thin la
作者
张同伟
罗欢
孟康
ZHANG Tongwei;LUO Huan;MENG Kang(Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,Austin,TX 78713,USA;School of Earth Sciences/Key Laboratory of Mineral Resources in Western China(Gansu Province),Lanzhou University,Lanzhou 730000,China;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China)
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2023年第3期1-13,共13页
Earth Science Frontiers
基金
国家自然科学基金重点项目“中国南方寒武系页岩有机质、流体和孔隙演化耦合机制研究(41730421)”。
关键词
页岩气
含气性
寒武系
有机孔
构造保存条件
中国南方
shale gas
gas content
Cambrian
organic pores
tectonic preservation conditions
southern China
