XIE, XINONG1, LI SITIAN¹, and DONG WEILIANG^2
1China University of Geosciences
²China Offshore Oil Nanhai West Corp.

Abstract: Evidence of Hot Fluid Flow in Diapiric Area in Overpressured System of Yinggehai Basin, South China Sea

The overpressure system developed over a large part of Yinggehai basin. The diapir structures were well developed and covered most of the central part of the basin. More than 20 diapir structures can be grouped into five rows distributing along S-N direction, which might indicate a close relationship with the dextral activity of the Red River fault system.

Thermal process could be classified into two zones in vertical, i.e. convective and conductive. The depth of the surface between convective and conductive zones ranges from 1480m to 2500m, which indicate the paleo-overpressured surface and is different in different diapiric structure. Along the surface, there are very sharp changes in thermal parameter, such as vitrinite reflectance (R_o), Rock-Eval Tmax and transfer rate from smectite to illite. In convective zone, R_o values abruptly increase with a steep gradient or multiple step gradient, and significantly higher than that in conductive zone. The jumping transition in smectite content in I/S mixed layer indicates the action of hot fluid flow At the same way, there is anomaly in Rock-Eval Tmax. Moreover, evidence of fluid inclusions also shows the multiple hot fluid expulsion. According to the integrated analysis, these diapir structures underwent multiple fluid expulsion, and have been confirmed to have great potential in gas.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas