石油与天然气地质2025，Vol.46Issue(5)：1410-1429,20.DOI:10.11743/ogg20250503
鄂尔多斯盆地陕北地区延长组长8与长9油层组烃源岩分布与地球化学特征及页岩油资源潜力评价
Geochemical characteristics,distribution,and shale oil resource potential of source rocks in the 8th and 9th oil groups of the Yanchang Formation,northern Shaanxi,Ordos Basin
摘要
Abstract
Using data from core observations,geochemical analysis,logging,crude oil physical properties,and well tests,we investigate the geochemical characteristics and spatial distribution of hydrocarbon source rocks in the 8th and 9th oil groups of the Yanchang Formation(also referred to as the Chang 8 and Chang 9 oil groups,respectively)in northern Shaanxi,Ordos Basin.The implications of tight oil accumulation within the lower hydrocarbon play of the Yanchang Formation in the study area are explored,and shale oil resources in the area are calculated.The results indicate that the silty mudstones,mudstones,and shales of the Chang 8 and Chang 9 oil groups contain total organic carbon(TOC)content ranging from 1.0％to 16.0％(average:4.8％),suggesting that they represent source rocks with organic matter abundance of good to excellent level.The kerogen of the source rocks exhibits type index(TI)values ranging from 47 to 92(average:70)and 813Ckerogen values from-25.9‰ to-29.8‰(average:-27.8‰),indicating a predominance of type Ⅱ 1 kerogen.The source rocks show peak hydrocarbon pyrolysis temperature(Tmax)ranging from 444 ℃ to 470℃(average:45℃ 6)and Ro values from 0.72％to 1.56％(average:1.16％),indicating that the organic matter is primarily in the mature to highly mature stage.Effective source rocks with TOC content＞1.0％and Ro values＞0.70％are identified across all oil sub-groups of the Chang 8 and Chang 9 oil groups.Among them,the Lijiapan shale of the Chang 9 oil group represents the most favorable source rocks,followed by shales of the 2nd and 1st oil sub-groups of the Chang 8 oil group(also referred to as the Chang 82 and Chang 81 oil sub-groups,respectively),as well as the Chang 9 oil group.The Lijiapan shale of the Chang 9 oil group thickens progressively from Dingbian to Ganquan,with thicknesses ranging from 4.0 m to 17.0 m(average:7.5 m).Its primary depocenters are located in Ganquan and southern Ansai,where zones with shale thicknesses exceeding 10.0 m cover an area of approximately 3 574 km2.In the Ganquan area,the Lijiapan shale of the Chang 9 oil group shows a thickness of up to a maximum of more than 35.0 m.The source rocks of the Chang 8 oil group are extensively developed in the Zhidan,Ganquan,and Fuxian areas,with those of the Chang 81 and Chang 82 oil sub-groups showing maximum single-layer continuous thicknesses exceeding 10.0 m and 30.0 m,respectively.Vertically,four types of source rock assemblages are identified within the lower hydrocarbon play of the Yanchang Formation:the Zhangjiatan shale(type A),the Zhangjiatan shale+the Lijiapan shale(type B),the Zhangjiatan shale+source rocks at the base of the Chang 82 oil sub-group+the Lijiapan shale(type C),and the Zhangjiatan shale+source rocks in the middle Chang 8 oil group+the Lijiapan shale(type D).Since source rocks act as both oil source rocks and cap rocks,the tight oil reservoirs of the Chang 8 oil group with source rock assemblages of types B,C,and D manifest favorable oil sources and strong sealing performance,which contribute to high tested oil production rates.Effective source rocks are further subdivided based on the oil saturation index(OSI)values,free hydrocarbon content(S1),chloroform bitumen"A"content,saturated hydrocarbon content,and aromatic hydrocarbon content of source rocks,as well as experience in the exploration and exploitation of the Gulong shale oil in the Daqing oilfield and international analogues.Specifically,effective source rocks with OSI values of greater than 100 mg/g,70～100 mg/g,and less than 70 mg/g are categorized as resources with readily movable(class Ⅰ),potentially movable(class Ⅱ),and hardly movable(class Ⅲ)shale oil,respectively.Silty mudstones are found bearing class Ⅰ shale oil due to their high hydrocarbon generation capacity and better reservoir spaces than mudstones and shales.The classes Ⅰ,Ⅱ,and Ⅲ shale oil resources in the study area are calculated at 0.38 × 109t,0.75 × 109t,and 2.95 × 109 t,respectively.关键词
地球化学特征/烃源岩/致密油/页岩油/长8油层组/长9油层组/陕北地区/鄂尔多斯盆地Key words
geochemical characteristics/source rock/tight oil/shale oil/8th oil group of the Yanchang Formation(Chang 8 oil group)/Chang 9 oil group/northern Shaanxi/Ordos Basin分类
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曹磊,闫新智,李辉,吴伟涛,白玉彬,赵子龙..鄂尔多斯盆地陕北地区延长组长8与长9油层组烃源岩分布与地球化学特征及页岩油资源潜力评价[J].石油与天然气地质,2025,46(5):1410-1429,20.基金项目
国家自然科学基金青年基金项目(42202185) （42202185）
中国博士后科学基金项目(2022MD713801) （2022MD713801）
陕西省教育厅科技计划项目(22JK0505). （22JK0505）
