Abstract: Mud-fluid diapir structures are developed in the Ledong-Lingshui sag in the Qiongdongnan Basin. Based on seismic interpretation result, the geometric morphology and genetic mechanism of the diapir structures in the Ledong-Lingshui sag and its periphery were analyzed, and the relation between the diapir structures and hydrocarbon accumulation was discussed. The development and evolution of the diapir structures in the Ledong-Lingshui sag is the result of the changes of regional tectonic stress feld and the formation of over pressure system. The over pressure system is the major factor controlling on the formation of the diapir structures. Two types of pressure relief modes control the types and distribution of the diapir structures; therefore,the diapir structures can be divided into two types:transportation and pressure relief through fractures, transportation and pressure relief through faults. The diapir structures formed by transportation and pressure relief through fracturesare chiefly distributed in banded style along the lower part of the central canyon channel, and the spatial coupling of the lower over pressure zone and the central canyon channel is the major element for forming this diapir belt. The diapir structures formed by transportation and pressure relief through faults are chiefly distributed along the faulted belts at northern and southern sides of the Ledong-Lingshui sag, and the centralized flowing and upwarping of plastic rock and fluid caused by the lower over pressure zone and the base fault activity are the major genesis of such diapir structures. The exploration practice in the Ledong-Lingshui sag indicates that the diapirs and faults are the major pathways for vertical hydrocarbon migration, the structural traps and lithological traps associated with diapirism are the favorable exploration targets that should be concerned in this area.

Key words: Ledong-Lingshui sag, mud-fluid diapir structure, over pressure system, diapirism, hydrocarbon accumulation