鄂尔多斯盆地奥陶系盐下储层中固体沥青的发现及其对天然气成藏的启示  

Discovery of solid bitumen in the Ordovician pre-salt reservoirs of the Ordos Basin and its implications for natural gas accumulation

作　　者：杨泽光 王爱国[1,2] 范立勇 马占荣[5] 罗晓容[1,2] 朱楠[1,2] 郭凯 张洁 YANG Zeguang;WANG Aiguo;FAN Liyong;MA Zhanrong;LUO Xiaorong;ZHU Nan;GUO Kai;ZHANG Jie(Department of Geology,Northwest University,Xi'an,Shaanxi 710069,China;State Key Laboratory of Continental Dynamics,Northwest University,Xi'an,Shaanxi 710069,China;National Engineering Laboratory of Low Permeability Oil and Gas Field Exploration and Development,Xi'an,Shaanxi 710018,China;Exploration and Development Research Institute,PetroChina Changqing Oilfield Company,Xi'an,Shaanxi 710018,China;Exploration Department,PetroChina Changqing Oilfield Company,Xi'an,Shaanxi 710018,China)

机构地区：[1]西北大学地质学系 [2]西北大学大陆动力学国家重点实验室 [3]低渗透油气田勘探开发国家工程实验室 [4]中国石油长庆油田公司勘探开发研究院 [5]中国石油长庆油田公司勘探事业部

出　　处：《天然气工业》2024年第2期68-80,共13页Natural Gas Industry

基　　金：中国石油长庆油田公司科技攻关项目“鄂尔多斯盆地中元古界—奥陶系构造沉积演化、成源机制与勘探新领域”(编号:ZDZX2021-05)。

摘　　要：近期,鄂尔多斯盆地奥陶系盐下地层取得了天然气重大勘探突破和新进展,已成为天然气勘探的重点新领域。但是,该领域天然气成因、资源潜力等关键成藏问题尚不清楚。为此,以鄂尔多斯盆地中东部奥陶系马家沟组五段7亚段—马家沟组四段(以下简称马五7亚段—马四段)为研究对象,通过岩心与显微镜观察,发现盐下储层中存在固体沥青,并明确了沥青的产状和地球化学特征,最后结合天然气地球化学分析,探讨了盐下地层中天然气(以下简称盐下天然气)的成因和资源潜力。研究结果表明:(1)奥陶系盐下储层中存在大量固体沥青,透射光显微镜观察沥青呈花状、片状、团块状、薄膜状或条带状赋存于白云岩和石灰岩的孔、缝、缝合线和沥青包裹体内,固体沥青的质量百分数介于0.07%~0.55%(平均值为0.17%),等效镜质体反射率介于1.75%~1.97%,碳同位素值介于-28.4‰~-27.7‰;(2)盐下天然气干燥系数介于0.95~1.00,为典型的干气,天然气的甲烷、乙烷和丙烷碳同位素值分别介于-44.8‰~-32.4‰、-31.1‰~-22.6‰和-28.8‰~-19.7‰,具有甲烷碳同位素偏轻、乙烷与丙烷碳同位素偏重的异常特征;(3)奥陶系盐下储层中的固体沥青和天然气均为石油热裂解成因,石油来自于马家沟组或更古老的地层,石油裂解发生在早白垩世中—晚期;(4)盐下天然气遭受了不同程度的硫酸盐热化学还原作用的改造,其中乌审旗地区改造程度较强,天然气中H2S含量高,最高可达13.31%。结论认为,马五7亚段—马四段天然气预测储量约为1.00×1012 m3,该盆地奥陶系盐下天然气勘探潜力巨大。Recently,with the significant breakthrough and new progress of natural gas exploration,the Ordovician pre-salt reservoirs in the Ordos Basin have become an important new field of natural gas exploration.However,the critical issues related to hydrocarbon accumulation in this field have not been understood yet,such as the origin and resource potential of natural gas.In this paper,core observation and microscopic analysis are carried out with the 7th Submember of the 5th Member of Ordovician Majiagou Formation and the 4th Member of Majiagou Formation(hereinafter referred to as Ma 57 Submember-Ma 4 Member) in the central and eastern Ordos basin as the research object.It shows the existence of solid bitumen in the pre-salt reservoir and clarifies the occurrence and geochemical characteristics of solid bitumen.And combined with natural gas geochemical analysis,the origin and resource potential of natural gas in pre-salt reservoirs(hereinafter referred to as pre-salt natural gas) are discussed.And the following research results are obtained.First,there is a large amount of solid bitumen in the Ordovician pre-salt reservoirs.Solid bitumen is observed by transmitted light microscope in the form of flowers,flakes,clumps,thin films or strips in pores,fractures,sutures,and bitumen inclusions of dolomite and limestone.The mass percentage of solid bitumen ranges from 0.07% to 0.55%(average 0.17%),the equivalent vitrinite reflectance ranges from 1.75%to 1.97%,and the carbon isotope value ranges from-28.4‰ to-27.7‰.Second,the drying coefficient of pre-salt natural gas ranges from 0.95 to 1.00,making it a typical dry gas.The carbon isotope values of methane,ethane and propane in natural gas range from-44.8‰ to-32.4‰,from-31.1‰ to-22.6‰,and from-28.8‰ to-19.7‰,respectively,presenting the abnormal characteristics of negative drift of methane carbon isotopes and positive drift of ethane and propane carbon isotopes.Third,both solid bitumen and natural gas in the Ordovician pre-salt reservoirs are the products of oil c

关 键 词：鄂尔多斯盆地 奥陶系 盐下地层 固体沥青 天然气成因 原油裂解 

分 类 号：P618.13[天文地球—矿床学]