摘要： 鄂尔多斯盆地奥陶系马家沟组四段(简称“马四段”)是下古生界天然气风险勘探的重点层位。文中基于岩心、薄片观察,结合地层对比、沉积结构描述等,并运用岩石结构组分测井解释和井震结合古地貌恢复等手段,对鄂尔多斯盆地马四段沉积时期古地貌、沉积特征和储集层展布进行了详细分析。结果表明: (1)受控于沉积期隆坳相间的古地貌格局,马四段发育大量台地内丘滩微相,其易于发生准同生溶蚀和白云石化作用,是储集层发育的有利相带;(2)马四段储集层以(藻)砂屑白云岩和粉—细晶白云岩为主,储集空间主要为粒间孔、晶间孔、溶蚀孔等;(3)纵向上,储集层主要分布于马四₂亚段和马四₁亚段;平面上,马四段储集层主要分布于台地内低凸起带和台缘带;(4)储集层的发育受控于3个因素,其中古隆起部位发育的有效丘滩体是储集层形成的物质基础,高频层序控制的准同生溶蚀作用是储集层形成的关键,白云石化是储集层后期保存的重要因素。马四段沉积时期碳酸盐岩台地内隆坳相间的古地貌控制了丘滩相带和白云岩储集层的展布,这一新认识为鄂尔多斯盆地下古生界天然气勘探提供了有力支撑,也为碳酸盐岩台地沉积储集层的研究提供了新思路。

关键词: 沉积微相, 白云岩储集层, 古地貌, 颗粒滩, 准同生溶蚀, 马家沟组, 鄂尔多斯盆地

Abstract: The Member 4 of Majiagou Formation(i.e. Ma₄ Member)of Ordovician in the Ordos Basin is the key target for risk exploration of natural gas in Lower Paleozoic. Based on the observation of core and thin section,the stratigraphic correlation,sedimentary structure description,well logging interpretation of rock structure and composition,and the combined well-seismic method for palaeogeomorphologic restoration,the palaeogeomorphology,sedimentary features and reservoir distribution of the Member 4 of Majiagou Formation in the Ordos Basin were analyzed in detail. Results show that: (1)Controlled by the palaeogeomorphologic pattern of uplift and depression in the depositional period,a lot of mound and bank microfacies developed in the Ma₄ Member and the penecontemporaneous dissolution and dolomitization were prone to occur,making it become the favorable sedimentary facies belt for reservoir development. (2)The reservoir of Ma₄ Member is mainly composed of(algal)arenaceous dolostone and silt-fine grain dolostone,and the reservoir space is mainly characterized as intergranular pores,intercrystal pores and dissolution pores. (3)The reservoirs are mainly distributed in Ma₄¹ and Ma₄² submembers,which are located at the low uplift belt in the platform and the platform margin belt. (4)The development of the reservoir is controlled by three factors.The mound-bank body developed in the palaeo-uplift is the material basis. The penecontemporaneous dissolution controlled by the high frequency sequence is the key to the formation of the reservoir,and dolomitization is an important factor for the preservation of the reservoir in the later period. The palaeogeomorphology of alternating uplift and depression in the carbonate platform during the Ma₄ depositional period controlled the distribution of mound-bank facies and dolomite reservoirs,which provided a strong support for gas exploration in the Lower Paleozoic,and also provides a new idea for the study of the sedimentary reservoir in the carbonate platform.

Key words: sedimentary microfacies, dolostone reservoir, palaeogeomorphology, grain beach, penecontemporaneous dissolution, Majiagou Formation, Ordos Basin

中图分类号: 

• P618.130.2+1