His work so completely occupied him that he didn’t have time to go out.

你看看划线部分是不是so + 副词。。。+that从句。被so强调的副词要在句子中作成分的。completely要修饰谓语动词，是修饰动词的下加状语，因此置于动词之前。如果将so completely移至him之后，则成了修饰性状语（方式状语），这样你就熟悉了，是吗？

His work occupied him so completely that he didn’t have time to go out.

其实，对so...that结构而言，二句是一样的。只不过副词completely一个是下加状语subjunct，一个是附加状语adjunct. 你不应该因为位置的不同就不认识so...that结构了。