渭河新生代盆地基底组成及其油气地质意义

(1.中国地质调查局 西安地质调查中心,陕西 西安 710054; 2.中国矿业大学(北京)地球科学与测绘工程学院,北京 100083; 3.西安石油大学 地球科学与工程学院,陕西 西安 710065; 4.陕西省地质调查院,陕西 西安 710054)

渭河盆地; 天然气; 晚古生代; 煤系地层

Basement composition for Weihe Cenozoic Basin and its petroleum geological significance
LI Yu-hong 1,2,ZHANG Wen1,2,YUAN Bing-qiang 3,HAN Wei1,CHEN Gao-chao1,ZHANG Lin4

(Cureau of Xi'an Geological Survey,China Geological Survey,Xi'an 710054,China; 2.College of Geoscience and Surveying Engineering,China University of Mining and Technology,Beijing 100083,China; 3.School of Earth Sciences and Engineering,Xi'an Shiyou University,Xi'an 710065,China; 4.Shaanxi Institute of Geological Survey,Xi'an 710065,China)

Weihe Basin; natural gas; late paleozoic; coal-bearing strata

DOI: 10.13800/j.cnki.xakjdxxb.2018.0613

备注

为进一步评价因缺乏有效烃源岩而停顿多年的渭河盆地的油气地质前景,结合区域地质背景,通过二维地震反射特征、地热井伴生气及油气化探的CH4,CO2碳同位素数据和钻探成果综合分析,认为渭河盆地深部残留有晚古生代含煤地层:二维地震反射剖面揭示,渭河盆地深部发育类似鄂尔多斯盆地石炭系—二叠系煤系地层强反射特征(T9),对应于太原组9#,8#和山西组4#,3#主力煤层的反射; 地热井伴生气及油气化探样品中δ13C(CH4)在-24.5‰ ~-40.2‰之间,属于煤型热解—裂解气,大多数样品δ13 CCO2<-10‰,属有机成因气; 渭参[3]井揭示盆内存在二叠系石盒子组,推测下部存在山西组和太原组地层; 渭河盆地在晚古生代为大华北克拉通的一部分,沉积有煤系地层,三叠纪末期开始遭受一定的隆升剥蚀,至新生代渭河断陷盆地形成后,盆地周缘发生大规模隆升剥蚀,而渭河盆地内这一时期接受了巨厚沉积,前新生代地层(上古生代煤系地层等)得以保存和深埋,即不同构造单元演化的差异造成了其地层剥蚀和残留程度的差异。综合认为晚古生代煤系地层甚至更晚层位存在于渭河盆地西安凹陷、固市凹陷和咸渭凸起的部分区域。渭河盆地晚古生代含煤地层可作为油气及氦气载体气的气源岩,为渭河盆地油气及富氦天然气勘探提供了物质基础,同时可为鄂尔多斯周缘断陷盆地群油气资源调查提供借鉴。

In order to continue the oil and gas prospect evaluation is Weihe Basin which has been stopped for many years due to the lack of effective source rocks,here we present the 2D seismic reflection characteristics,carbon isotopes of CH4 and CO2 from associated gas of geothermal wells and oil and gas geochemical exploration,and drilling results.Combined with the regional geological background,Late Paleozoic coal-bearing strata(LPCS)are demonstrated to present in the deep of Weihe Basin:Seismic reflection profiles show that there are strong reflection features similar to C-P coal-bearing strata in Ordos Basin,corresponding to the main coal seam in Taiyuan Formation(No.9,8)and Shanxi Formation(No.4,3).For the associated gases in geothermal wells and samples of oil and gas geochemical exploration,δ13CH4ranges from -24.5‰ to -40.2‰,classified as coal-related pyrolysis and cracking gas; Majority of δ13 Cco2 lower than-10‰,classified as organic gas.WC3 well reveals the presence of Permian Shihezi Formation,suggesting the existence of Shanxi Formation and Taiyuan Formation.In Late Paleozoic,Weihe Basin was a part of Great North China Craton,depositing coal-bearing strata; Since the end of Triassic,the region experienced uplift and erosion to some extent; In Cenozoic,surroundings experienced large-scale uplift and erosion whereas the graben basin subjected to thick sediments,preserving the pre-Cenozoic strata(including the LPCS).And the different evolution of tectonic units results in their different erosion and preservation.It is concluded that the LPCS and even later layers exist in the the part ofXi'an depression,the Gushi depression and the Xianwei uplift.The LPCS of the Weihe Basin are the source rocks for hydrocarbon and helium carrier gas,which provide material basis for the exploration of hydrocarbon and rich helium natural gas in the Weihe Basin,further provide reference for the graben basins around Ordos Basin.