Impermeable formations, such as shales and siltstones, tend to be finer grained or of a mixed grain size, with smaller, fewer, or less interconnected pores.
不渗透的地层如页岩与粉砂岩。因颗粒很细或粗细颗粒混杂。只有较小，较少连通不好的孔隙。
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The alternative approach is simpler but does not provide as fine-grained control. Since the two approaches manage line buffering differently, they should not be mixed.