鄂尔多斯盆地东部下奥陶统马家沟组盐下含气系统特征与勘探潜力  

Characteristics and exploration potential of subsalt gas-bearing system in Majiagou Formation of Middle Ordovician in the eastern Ordos Basin

作　　者：周进高 李明瑞[3] 吴东旭 于洲 张杰[1,2] 张涛[3] 李维岭 丁振纯 ZHOU Jingao;LI Mingrui;WU Dongxu;YU Zhou;ZHANG Jie;ZHANG Tao;LI Weiling;DING Zhenchun(PetroChina Hangzhou Research Institute of Geology,Hangzhou,Zhejiang 310023,China;CNPC Key Laboratory of Carbonate Reservoir,Hangzhou,Zhejiang 310023,China;PetroChina Changqing Oilfield Company,Xi'an,Shaanxi 710018,China)

机构地区：[1]中国石油杭州地质研究院 [2]中国石油集团公司碳酸盐岩储层重点实验室 [3]中国石油长庆油田公司

出　　处：《天然气工业》2023年第3期34-45,共12页Natural Gas Industry

基　　金：国家科技重大专项“寒武系—中新元古界碳酸盐岩规模储层形成与分布研究”(编号:2016ZX05004-002);中国石油天然气集团有限公司上游领域基础性前瞻性项目“残留型海相盆地构造—岩相古地理重建技术研究”(编号:2021DJ0501);中国石油长庆油田公司重大专项“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:技2021-90)。

摘　　要：奥陶系下统马家沟组是鄂尔多斯盆地下古生界重要产气层位,目前已在马家沟组盐上风化壳领域获得了近万亿立方米的天然气地质储量,且盐上组合研究成果丰富,认识较为统一。但是,马家沟组盐下组合含气系统研究不足和认识分歧较大,已严重制约了该区盐下天然气的勘探。为此,从天然气地球化学特征出发,利用地质、地球物理和地球化学手段,对盐下含气系统进行了系统研究;结合盐下天然气来源、烃源岩规模和储层特征以及圈闭成藏要素评价,明确了马家沟组盐下天然气成藏的有利条件和富集区带。研究结果表明:(1)马家沟组盐下天然气的甲烷、乙烷碳同位素偏轻,具有典型油型气特征,其烃源岩可能为马家沟组高频层序相关的薄层海相烃源岩,岩性主要为暗色泥质白云岩和微生物白云岩,具备规模供烃能力;(2)盐下发育多套丘滩和丘坪粉晶白云岩储层,沿台内低隆规模分布,源储盖组合反映盐下具备自生自储成藏条件,疏导断层、侧向封堵是成藏关键要素;(3)榆林—横山和神木—米脂地区是盐下天然气有利富集区带。结论认为,马家沟组盐下含气系统和天然气富集区带新认识的提出有效地支撑了米探1井的天然气勘探突破,对鄂尔多斯盆地深层天然气深化勘探具有重要指导意义。The Majiagou Formation of Lower Ordovician is an important gas-producing horizon of Lower Paleozoic in the Ordos Basin.So far,nearly trillions of cubic meters of natural gas geological reserves have been obtained in the field of Majiagou Formation supra-salt weathering crust.Moreover,the research results of supra-salt assemblage are rich and the understandings are accordant.However,the insufficient research and divergent understanding on the gas-bearing system of Majiagou Formation sub-salt assemblage seriously restrict the exploration of sub-salt natural gas in this area.Based on the geochemical characteristics of natural gas,this paper systematically researches the sub-salt gas bearing system by means of geology,geophysics and geochemistry.Then,the favorable accumulation conditions and enrichment zones of Majiagou Formation sub-salt natural gas reservoirs are determined by analyzing the sub-salt natural gas origin,the source rock scale and reservoir characteristics and by evaluating trap accumulation factors.And the following research results are obtained.First,the Majiagou Formation sub-salt natural gas is relatively light in carbon isotopes of methane and ethane,presenting the typical characteristics of oil-type gas.The hydrocarbon source rock may be acted by the thin marine source rock related to the high-frequency sequence of Majiagou Formation,which is lithologically dominated by dark argillaceous dolomite and microbial dolomite and has the capacity of large-scale hydrocarbon supply.Second,multiple sets of mound beach and mound flat powder crystal dolomite reservoirs are developed under the salt,and distributed along the low uplift in the platform in a large scale.The source-reservoir-cap assemblage reflects the hydrocarbon accumulation conditions of self-generation and self-storage under the salt,and the key factors of hydrocarbon accumulation are dredging faults and lateral sealing.Third,Yulin-Hengshan and Shenmu-Mizhi areas are favorable enrichment zones of sub-salt natural gas.In conclusion,the new und

关 键 词：鄂尔多斯盆地 下奥陶统 马家沟组 油型气 烃源岩 含气系统 勘探潜力 米探1井 

分 类 号：P618.13[天文地球—矿床学]