鄂尔多斯盆地苏里格地区奥陶系马家沟组马五_(5)亚段沉积特征

Sedimentary characteristics of Ma 5_(5) sub-member of Ordovician Majiagou Formation in Sulige area,Ordos Basin

鄂尔多斯盆地苏里格地区奥陶系马家沟组马五5亚段勘探潜力巨大。通过岩心观察、薄片鉴定、扫描电镜分析和地球化学测试,结合地球物理技术,对苏里格地区奥陶系马家沟组马五_(5)亚段沉积特征进行了系统研究,探讨了其油气地质意义。研究结果表明:(1)苏里格地区奥陶系马家沟组马五_(5)亚段属于整体海侵、晚期海退沉积背景下的向东倾斜的碳酸盐岩台地相,发育开阔台地和局限台地等亚相,可根据成分细分为云坪、灰坪和台内滩、云灰坪、灰云坪等微相。(2)研究区平面上沉积环境呈典型条带状展布,西部地区沉积水体盐度偏高,具有局限台地特征;东部地区沉积水体盐度偏低,具有开阔台地特征。(3)研究区的局限台地与开阔台地内部的低洼区域,高密度富Mg海水汇聚,为白云岩发育的有利区。(4)局限/开阔云坪相、台内滩和含膏云坪微相主要发育各种白云岩储层,连片发育白云岩的西、北部地区是潜在的油气勘探接替领域。

The exploration potential of Ma 5_(5) sub-member of Ordovician Majiagou Formation in Sulige area of Ordos Basin is huge.Through core observation,thin section identification,scanning electron microscope and geochemical testing,combined with geophysical technologies,the sedimentary characteristics of Ma 5_(5) sub-member of Ordovician Majiagou Formation in Sulige area were studied,and its petroleum geological significance was discussed.The results show that:(1)The Ma 5_(5) sub-member of Ordovician Majiagou Formation in Sulige area belongs to carbonate platform facies which inclines to the east under the background of overall transgression and late regressions.Open platform and restricted platform subfacies are developed,which can be subdivided into dolomite flat,carbonate flat,and intraplatform shoal,dolomite-carbonate flat and carbonate-dolomite flat according to the composition.(2)In the plane,the sedimentary environment is typical banded distribution,the salinity of the sedimentary water in the western region is relatively high,with restricted platform characteristics,while the salinity of the sedimentary water in the eastern region is low and has the characteristics of open platform.(3)The low-lying areas within the restricted platform and the open platform in the study area,where high-density and Mg-rich seawater converges,are favorable areas for dolomite development.(4)The restricted/open dolomite flat,intraplatform shoal and gypsum-bearing dolomite flat microfacies mainly develop various kinds of dolomite reservoirs.The western and northern areas with contiguous dolomites are potential replacement areas for oil and gas exploration.