Geochemical characteristics of the fluid inclusions in the Gangxi Fault Belt, Huanghua Depression, Bohai Bay Basin, China

We studied the geochemical characteristics of the fluid inclusions in the Ordovician carbonates and the Oligocene Shahejie Formation sandstones from 15 wells in the Gangxi Fault Belt, Huanghua Depression. The fluid inclusions are all sec- ondary with gas/liquid ratio of 5%~10%. Base on Raman they are mainly composed of H2O, CO2 and CH4. The homogenization temperatures, combined with burial and geothermal history of the host rock, indicate that the fluid flows in the Shahejie Formation and the Ordovician carbonates were trapped in Neocene. Using a VG5400 mass spectrometer, the helium isotopic compositions were analyzed. Interpretation of results suggested a significant amount of mantle-derived helium mainly accumulating in the intersections of the NWW trending Xuzhuangzi and NE trending Gangxi faults. The maturity of hydrocarbon decreases from the intersection to the outside pointing out that the fluid related to the NWW trending Xuzhuangzi and NE trending Gangxi faults. These factors implied the fluid inclusions have a close relationship to the local tectonic setting. Gangxi Fault Belt experienced intensive Neo-tectonic activities in Cenozoic. Widespread faulted-depressions and strong volcanic eruptions manifested its tec- tonic status of extensional stress field. Mantle uplift caused the movement of magma that carried mantle-derived gases and deep heat flows, the deep-rooted tension faults provided the passages for the gases and heat flows to shallow crust levels.

黄骅坳陷港西断裂带流体包裹体的地球化学特征

通过对黄骅坳陷港西断裂带奥陶系灰岩和新近系沙河街组砂岩中11个钻井的岩心包裹体的特征,均一温度和组分等方面的分析,对其所反映的气体来源,形成环境,油气演化以及地质意义进行研究。研究区的包裹体均为次生成因包裹体,气液比在5%～10%之间,根据激光拉曼光谱技术分析组分主要为 H_2O,CO_2和 CH_4。利用均一温度,结合古地温和埋藏史,发现奥陶系灰岩和新近系沙河街组砂岩中包裹体中流体均捕获于新近纪。对氦同位素的分析发现包裹体中均有幔源氦的侵入,侵入的份额受到 NE 向港西断层和 NWW 向徐庄子断层的控制靠近断裂带的灰岩和砂岩中的包裹体含有还原性气体,由断层交汇中心向四周减少。包裹体中烷烃气的成熟度也与断层活动相关,具有从断层交汇中心向四周减小的相似特征。研究区内港西断层和徐庄子断层交汇处不仅是幔源气体上涌的有利通道,也是地热活动强烈的地区,有利于烷烃气的成熟。