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盖层对气藏的保存极为重要，其封盖能力的优劣决定了气藏的“存亡”。盖层的宏观封闭性是指盖层厚度、岩性、纵横向分布等宏观特征所体现出来的封闭能力，是盖层封闭能力的最直接表现，也是控制大中型气田（藏）分布的主要因素之一。鄂尔多斯盆地中部上古生界石炭—二叠系煤系地层中天然气资源十分丰富，针对该层系的勘探工作可以为大气田提供重要的后备储量，改变气田储量丰度偏低的状况。应用模糊数学方法，对陕甘宁盆地中部上古生界８个层段的盖层宏观封闭性进行了评价。结合实钻资料分析表明，该区上古生界试气较好的井大部分在封闭性隶属度高值区内，对气层封盖起重要作用的是上古生界及其上的泥质岩；上二叠统上石盒子组的封闭隶属度值明显高于其他层段，并且对区域性天然气富集有控制作用。研究结果可揭示上古生界气藏的形成及分布规律。

A STUDY ON THE MACRO CLOSING PROPERTY OF THE CAP ROCKS OF UPPER PALEOZOIC GAS RESERVOIRS IN THE CENTRE OF SHAANGAN NING BASIN BY USE OF FUZZY MATHEMATICAL METHOD

??Cap rock is very important for preserving a gas reservoir and the "life-or-death"of the gas reservoir is depended upon whether the closing property of the cap rock is good or not.The macro closing property of the cap rock means the closing capacity embodied by the macro characteristics as the thickness and lithology of the cap rock and its vertical and horizontal distribution, etc., being the most direct expression of the closing capacity of the cap rock and being one of the main factors of controlling the distribution of large-and medium-sized gas fields/reservoirs.The natural gas resources are very abundant in the Carboniferous-Permian coal measure strata of the Upper Paleozoic in the centre of Eerduosi Basin.The exploration work aiming at the strata can provide significant backing reserves for the large gas field and change the condition of the lower reserve abundance.The macro closing property of the cap rocks in eight intervals of the Upper Paleozoic in the centre of Shaanganning Basin is evaluated by use of fuzzy mathematical method.In combination with the analysis of drilling data, it is shown that in this region, most of the wells with a good result of well testing are located at the high value areas of closing property subordinateness and the argillaceous rocks in the Upper Paleozoic and its overlying strata play an important role in sealing the gas reservoirs.The values of closing property subordinateness in the Upper Shihezi Formation of Upper Permian are much higher than those in the other intervals, which controls the regional natural gas accumulation.Thus, the formation and distribution laws of the Upper Paleozoic gas reservoirs are further revealed.