鄂尔多斯盆地东南部延长组七段页岩发育特征及勘探潜力

鄂尔多斯盆地油气资源丰富,延长组七段(长七段)发育的优质烃源岩是该盆地页岩气的重点勘探层系。前期对盆地东南部长七段页岩发育特征缺乏系统分析,不能准确反映研究区页岩气勘探潜力。为此,以鄂尔多斯盆地东南部长七段页岩为研究对象,在页岩发育特征研究的基础上,综合采用岩相法和五项指标法,从页岩的生气潜力、储气潜力和开发潜力3个方面进行评价。岩相法用于评价储气潜力,通过页岩的总有机碳含量、脆性矿物(石英、长石和碳酸盐等)含量和黏土矿物相对含量,将长七段页岩划分为四大类,其中深色富有机质脆性页岩的开发潜力最高。五项指标法通过选用不同的五项指标组合,对生气潜力和开发潜力进行评价;其中,生气潜力评价指标为吸附气比例、有机质转化率、气体干燥系数、总有机碳含量和镜质组反射率;选取页岩的厚度、脆性矿物含量、地层压力系数、总有机碳含量和镜质组反射率五项指标分析页岩的开发潜力。综合2种方法获得的分析结果,优选出N3,N5,N6,N7和N10为研究区长七段页岩最有利的5个高勘探潜力层段。

Development characteristics and exploration potential of shale in Chang7 Member in southeast of Ordos Basin

Ordos Basin is rich in hydrocarbon resources,in which the organic-rich shale in Chang7 Member of Yanchang Formation is an important stratum for shale gas exploration.The previous studies lack systematic analysis of the shale in Chang7 Member in the southeast of Ordos Basin,which fail to accurately reflect the real exploration potential of shale.Based on the analysis of development characteristic,we take the shale in Chang7 Member in the southeast of Ordos Basin as the research object to evaluate its exploration potential from three aspects:gas generation potential,gas storage potential,and development potential by petrographic analysis and the five-index methods.The petrographic analysis is used to evalu?ate gas storage potential.In terms of total organic carbon content,content of brittle minerals(quartz,feldspar,carbonate,etc.),and relative content of clay minerals,the shale in Chang7 Member is divided into four categories,among which dark organic-rich brittle shale has the highest development potential.The five-index method is adopted to evaluate gas genera?tion potential and development potential through the combination of five indexes.The indexes for evaluating gas generation potential are gas absorption ratio,organic-matter conversion rate,gas drying coefficient,total organic carbon content,and vitrinite reflectance;those for development potential are shale thickness,content of brittle minerals,formation pressure coef?ficient,total organic carbon content,and vitrinite reflectance.Finally,the data obtained by the two methods are combined to select five horizons with the most favorable exploration potential of shale in Chang7 Member:N3,N5,N6,N7,and N10.