文章编号:1671-1505(2005)01-0034-11 文献标识码:A鄂尔多斯盆地西南地区上三叠统延长组沉积相及石油地质意义付金华1,2 郭正权2 邓秀芹21西北大学地质系,陕西西安 7100692中国石油长庆油田分公司勘探开发研究院,陕西西安 710021摘 要 鄂尔多斯盆地三叠系延长组主要发育东北和西南两大沉积体系,东北的河流三角洲体系已为大量的勘探研究资料所证实,而西南体系因受勘探程度限制,目前研究不够。
本文通过最新钻探成果,结合盆地西南部露头资料,确立盆地西南地区三叠系延长组为冲积扇-扇三角洲沉积体系,发育冲积扇、扇三角洲、湖泊(浊积)相。
冲积扇以西南缘平凉崆峒山和水河剖面为代表,扇三角洲及湖泊(浊积)相为区内钻井剖面所证实。
长6—长8为区内主力油层组,地层保存完整,钻探程度相对较高。
扇三角洲前缘砂体类型以水下分流河道为主,局部发育河口坝。
浊积体以厚层块状为主。
长8亚期为扇三角洲前缘亚相最发育期,横向形成自西南向东北延伸的三支前缘砂体带,是石油聚集的重要区带;长7亚期随着湖盆沉降,周边抬升强烈,湖岸较陡,大量发育浊积体系;长6亚期湖退导致扇三角洲再次发育,但规模较长8亚期小。
扇三角洲前缘砂体单层厚度大,砂岩粒度较粗,颗粒分选及物性好,是石油富集的最有利相带。
关键词 鄂尔多斯盆地 上三叠统 沉积相 冲积扇 扇三角洲 浊积第一作者简介 付金华,男,1963年生,1982年毕业于江汉石油学院勘探系,现为西北大学在读博士,长庆油田分公司勘探开发研究院教授级高工,主要从事油气勘探地质研究。
Sedimentary facies of the Yanchang Form ation of Upper T riassicand petroleum geological implication in southw estern Ordos B asinFu Jinhua 1,2 Guo Zhengquan 2 Deng Xiuqin 21Depart ment of Geology ,Northwest U niversity ,Xi ’an 710069,S haanxi2Research Institute of Pet roleum Ex ploration and Development ,Changqing Oilf ield Com pany ,Pet roChina ,Xi ’an 710021,S haanxiAbstract In the Yanchang Formation of Triassic in the Ordos Basin mainly two sedimentary sys 2tems are developed :the northeastern and southwestern systems 1It has been proved that the northeast 2ern sedimentary system is a river delta system through abundant research data 1However ,the south 2western system is little studied as there has been only limited efforts in exploration 1Based on the latest drilling and outcrop data ,it has been concluded that the southwestern sedimentary system in the Or 2dos Basin is an alluvial fan 2fan delta system and the alluvial fan ,fan delta and lake facies or turbidite facies were developed 1The alluvial fan is typical in the sections of Pingliang K ongdongshan and Ruishuihe River 1The fan delta and lake facies or turbidite facies are proved by observation on the drilling sections in the study area 1The main reservoirs include the intervals Chang 6to Chang 8and the第7卷 第1期2005年 2月古地理学报JOURNAL OF PALAEO GEO GRAPHYVol 17 No 11Feb 1 2005strata are preserved integration with relatively high intensity of drilling efforts1The subaqueous dis2 tributary channel is the main type of the fan delta front while the channel mouth bar is developed local2 ly1The turbidite sandstone is mainly thick2bedded1Fan delta front subfacies was best developed during the Chang8Subage1Three delta front sandbody belts are formed from southwest to northeast and they are the important areas where hydrocarbon accumulates1The turbidite system was well developed in the Chang7Subage because the lake basin subsided,the periphery was uplifted strongly and the lakeshore was very steep1The fan delta was developed again because the lake regression occurred during the Chang6Subage,but the scale was smaller than that of the Chang8Subage1The fan delta front sandbody is the most advantageous zone of petroleum accumulation because of its great thickness, coarse grainsize,well sorting and good physical properties1K ey w ords Ordos Basin,Upper Triassic,sedimentary facies,alluvial fan,fan delta,turbidite About the f irst author Fu Jinhua,born in1963,was graduated from the Department of Explo2 ration in Jianghan Petroleum Institute1Now he is a senior engineer at the Research Institute of Explo2 ration and Development of Changqing Oilfield Company,PetroChina and is mainly engaged in the geo2 logical research for petroleum exploration11 前 言鄂尔多斯盆地是我国典型的克拉通沉积盆地。
在经历了早古生代浅海台地和晚古生代的近海湖盆发育之后,段,尤其是晚三叠世延长期,是湖盆发展的全盛期,湖盆底形呈西陡东缓的箕状,在东北、西南两大物源控制下,形成了以东北河流三角洲、西南扇三角洲为代表的两大沉积体系(何义中等,2001;张春生等,2000;魏红红等,2002;宋凯等,2003)。
按沉积旋回将延长组自上而下分为10个油层组,依次为长1到长10(表1),其沉积特征反映了湖盆形成、发展和消亡的演化全过程。
长9、长7、长4+5亚期是湖盆演化中的三大湖侵期,尤其是长7亚期,湖侵达到鼎盛期,沉积了盆地中生界最好的烃源岩。
三大湖侵期之间是岸进期,以长8、长6、长3亚期为代表,形成了重要储集层系。
盆地东北及中部广大地区经过多年综合研究和勘探证实,主要为一套河流相和三角洲相沉积,而盆地西南陇东地区(图1)延长组,因勘探程度较低而缺少系统的沉积相研究。
本文通过盆地西南缘崆峒山、水河、策底坡等露头,结合区内100余口钻井剖面、岩心、测井等资料对延长组特别是长8到长6的沉积相进行了细致的划分,并探讨沉积相的分布演化河三角洲(宋凯等,2002;武富礼等,2004),又区别于辫状河三角洲(武富礼等,2004)和水下扇Ξ。
图1 研究区构造位置图Fig11 The tectonic location of the study area第7卷 第1期付金华等:鄂尔多斯盆地西南地区上三叠统延长组沉积相及石油地质意义35表1 延长组地层简表Table1 The stratigraphy of the Y anchang Formation地 层系统组油层组厚度/m岩 性三 叠 系上三叠统延长组长10～240 暗色泥岩、泥质粉砂岩、粉细砂岩不等厚互层,夹碳质泥岩及煤线长2120～150 灰绿色、浅灰色细砂岩夹暗色泥岩长390～110 浅灰、灰褐色细砂岩夹暗色泥岩长4+580～100 浅灰色粉细砂岩与暗色泥岩互层长6120～150 褐灰色块状细砂岩夹灰黑色泥岩,泥质粉砂岩、粉细砂岩互层夹薄层凝灰岩长780～100 暗色泥岩、碳质泥岩、油页岩夹薄层粉细砂岩长870～85 暗色泥岩、砂质泥岩夹灰色粉细砂岩长990～120 暗色泥岩、页岩夹灰色粉细砂岩长10280～350 灰色厚层块状中细砂岩、粗砂岩,麻斑结构中三叠统纸 坊 组 灰紫色泥岩、砂质泥岩与紫红色中细砂岩互层2 沉积相特征根据各种沉积相识别特征(冯增昭等,1994;焦养泉等,1998;魏红红等,1999)以及陆相湖盆主要沉积体系划分方案(裘亦楠和肖劲修,1982;中国石油学会石油地质委员会编译,1986;杨小萍和陈丽华,2001),并结合钻井、测井资料及3条周缘露头剖面资料,对盆地西南地区的沉积相进行分析,并划分出冲积扇、扇三角洲、湖泊浊积相等类型。