The origins of overpressure in the central Xihu depression have been accepted to result from disequilibrium compaction and hydrocarbon generation. This study uses organic matter correction of the log data in source rocks and five empirical methods (the multilogging combination method, Bowers’ method, the sonic velocity–density crossplot method, the porosity method, and the pressure inversion method) to understand the origins of overpressure in the central Xihu depression. Overpressure strata are mainly distributed in the following two areas: the (1) Pinghu Formation on the western slope of the central Xihu depression and (2) Pinghu Formation and lower part of the Huagang Formation in the western sag and the central inversion anticline belt. The areas contain two types of pressure profiles: normal pressure–overpressure and normal pressure–overpressure–normal pressure. At the western slope and the western sag, overpressure in source rock and nonsource rock was caused by hydrocarbon generation and pressure transfer, respectively. At the central inversion anticline belt, however, overpressure was caused by hydrocarbon generation and tectonic compression in source rock and by pressure transfer and tectonic compression in nonsource rock. We also propose criteria for confirming the combination of tectonic compression and hydrocarbon generation as the origin of overpressure, where the porosity distribution in the overpressured mudstone is consistent with the normal compaction trend or conforms to a higher level of normal compaction as the depth increases. In the sonic velocity–effective stress diagram, sonic velocity increases with decreasing effective stress, whereas density and sonic velocity both increase with increasing normal compaction in the density–sonic velocity diagram.

中文翻译：

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东海陆架盆地西湖坳陷中部超压成因

西湖坳陷中部超压的成因已被认为是不平衡压实和生烃的结果。本研究利用烃源岩测井数据的有机质校正和 5 种经验方法（多次测井组合法、Bowers 法、声速-密度交会法、孔隙度法和压力反演法）来了解西湖坳陷中部超压。超压地层主要分布在以下两个区域：（1）西湖凹陷中部西坡的平湖组；（2）西部凹陷和中央反转背斜带的平湖组和花港组下部。这些区域包含两种类型的压力剖面：常压-超压和常压-超压-常压。在西部斜坡和西部凹陷，烃源岩和非烃源岩的超压分别是由生烃和压力传递引起的。而在中央反转背斜带，超压是由烃源岩中的生烃和构造压缩以及非烃源岩中的压力传递和构造压缩引起的。我们还提出了确认构造压缩和生烃相结合作为超压起源的标准，其中超压泥岩中的孔隙度分布与正常压实趋势一致或随着深度的增加符合更高水平的正常压实。在声速-有效应力图中，