Observation of Catastrophic Degassing from Mantle-Crust in Yinggehai Basin, South China Sea

作     者：ChenHonghan JohnParnell GongZaisheng LiSitian 

作者机构：FacultyofEarthResourcesChinaUniversityofGeosciencesWuhan430074China DepartmentofGeology＆PetroleumGeologyUniversityofAberdeenAberdeenAB243UEUK ChinaNationalOffshoreOilCorp.Beijing100027China FacultyofEarthResourcesChinaUniversityofGeosciencesWuhan430074China 

出 版 物：《Journal of China University of Geosciences》 (中国地质大学学报（英文版）)

年 卷 期：2004年第15卷第3期

页      面：295-305页

核心收录：

学科分类：070904[理学-构造地质学] 0819[工学-矿业工程] 0709[理学-地质学] 081903[工学-安全技术及工程] 07[理学] 08[工学] 

基　　金：ThispaperisjointlysupportedbytheNationalNaturalScienceFoundationofChina (Nos.40 2 380 60and 40 372 0 68) 

主　　题：carbon dioxide and helium degassing from mantle and crust Yinggehai basin. 

摘      要：To lower the CO 2 risk for hydrocarbon exploration in the west continental shelf of Yinggehai basin, South China Sea, we do attempt not only to know the CO 2 origins, but also to make an understanding of the degassing processes from the mantle and crust. Based on the stable carbon isotope ratios of CO 2 alone, the organic and inorganic CO 2 can be successively distinguished, but the formation conditions and mixing processes for inorganic CO 2 are still not clear. The relationships between lg[R(= 3He/ 4He)/R a(=1.386×10 -6)] and CO 2 content (%), CO 2/ 3He and δ 13C CO 2 have been employed, respectively, to obtain that the CO 2 gases in the reservoirs can be classified into three categories: (1) organic CO 2 with very low contents but contaminated by mantle-derived helium; (2) inorganic CO 2 gases with lower to higher contents being mixtures of crustal CO 2 with mantle-derived CO 2, the mantle- contributed percentage being in the range of 0 %-27 %, and (3) mainly crust-derived inorganic CO 2 gases being characterized by high contents (more than 50 %) and indicating the crustal addition by metamorphism of rich-in carbon rocks in basement. Nevertheless, some CO 2/ 3He ratios of organic CO 2 fall into the range 10 8-10 10, which made us inquire whether the CO 2/ 3He=(1-10)×10 9 can be the unique signature of magmatic CO 2 or not. All the observation of plutonic activities, fluid inclusion measurements in gas reservoirs, pre-stack depth/time seismic sections and the satellite infrared remote photography taken from Yinggehai basin, South China Sea, during Chichi earthquake in Taiwan on September 21, 1999, supports that the degassing processes are in a discontinuous mode, which may be triggered by igneous intrusion or extrusion, or earthquakes. In the central diapir zone of the basin, at least 3 to 4 orders of discharge of across-formational thermal fluid flows through fractures can be determined in different scales. The mantle de