鄂尔多斯盆地陇东地区铝土岩天然气勘探突破与油气地质意义探索

Breakthrough in the exploration of bauxite gas reservoir in Longdong area of the Ordos Basin and its petroleum geological implications

近期,中国石油长庆油田公司在鄂尔多斯盆地西南部陇东探区古生界部署的L47井获得67.38×10^(4)m^(3)/d的高产工业气流,标志着该区铝土岩天然气勘探获重大突破。为了进一步明确铝土岩天然气勘探开发潜力,在铝土岩岩心、野外露头、录井、测井、分析化验资料的基础上,系统研究分析了储层、烃源岩及圈闭的特征,探索了铝土岩天然气的成藏控制因素,并对盆地西南部古生界铝土岩天然气勘探潜力做出评价。研究结果表明:①鄂尔多斯盆地铝土岩天然气勘探突破得益于源内非常规勘探思路的转变,为该盆地天然气勘探开辟了新领域;②铝土岩储层的主要储集空间类型为溶蚀孔,储层受沉积古环境和古地貌控制,潟湖环境中沉积厚层的铝土岩成矿物质,古地貌低部位,有利于优质铝土岩储层的发育;③上古生界煤系烃源岩为主要的气源岩,它与古生界铝土岩储层直接或间接接触,源储配置关系良好;④气藏的主要圈闭类型为岩性圈闭,在燕山期盆地东部构造抬升背景下,铝土岩储层上倾方向存在岩性相变有效遮挡条件。结论认为,铝土岩天然气勘探突破不仅为长庆油田天然气增储上产增添了“底气”,还对华北其他地区铝土岩天然气勘探具有重要的启示意义。

Recently,high-yield industrial gas flow is produced at a rate of 67.38×10^(4)m^(3)/d by Well L47 which is deployed by PetroChina Changqing Oilfield Company in the Paleozoic in Longdong exploration area of the southwestern Ordos Basin,marking a great breakthrough in the exploration of bauxite gas reservoirs in this area.In order to further clarify the exploration and development potential of bauxite gas reservoirs,this paper systematically analyzes the reservoir characteristics,source rocks and traps based on the data of bauxite cores,field outcrops,mud logging,wireline logging and assay.In addition,the factors controlling the formation of bauxite gas reservoirs are explored,and the exploration potential of Paleozoic bauxite gas reservoirs in the southwestern Ordos Basin is evaluated.And the following research results are obtained.First,the breakthrough in the exploration of this bauxite gas reservoir in the Ordos Basin benefits from the change of the intra-source unconventional exploration idea,which starts a new field of gas exploration in the Ordos Basin.Second,this bauxite reservoir is controlled by sedimentary paleoenvironment and paleogeomorphology and its reservoir space is dominated by dissolution pores.Thick layers of bauxite diagenetic mineral are deposited in the environment of lagoon.There are favorable conditions for the development of high-quality bauxite reservoirs in the low position of paleogeomorphology.Third,the Upper Paleozoic coal-measure source rocks are the main gas source rocks,which are in direct or indirect contact with the Paleozoic bauxite reservoir,so a good source-reservoir configuration relationship is formed.Fourth,the main trap type of gas reservoir is lithologic trap.In the background of tectonic uplift in the eastern Ordos Basin in the Yanshanian period,there is an effective barrier of lithofacies change in the updip direction of the bauxite reservoir.In conclusion,the breakthrough in the exploration of bauxite reservoir not only makes Changqing Oilfield more confident in natural gas reserve and production increase,but it is also of important implications for the exploration of bauxite gas reservoirs in other areas of North China.