黄骅坳陷新生代构造活动对无机成因CO_2气藏控制作用的研究

Cenozoic Tectonic Control on the Abiogenic CO_2 Gas Deposits, Huanghua Depression

通过研究黄骅坳陷新生代的构造活动 ,对黄骅坳陷无机成因二氧化碳气藏的形成与分布特征进行分析 ,发现黄骅坳陷无机成因CO2 成藏与断裂和岩浆活动密切相关。新生代的NE—NEE向的伸展断裂为幔源型二氧化碳提供了良好的通道 ,尤其是在这些NE—NEE向伸展断裂与NW向断裂的交汇处 ,有利于二氧化碳的运移和聚集 ;同时这些伸展断裂往往是地热较高的区域 ,有利于热变质成因二氧化碳的生成 ;岩浆作用不仅可以直接释放来自幔源的二氧化碳气体 ,而且岩浆作用带来的地热也可以促进碳酸盐岩的热变质作用 ,释放二氧化碳。同时 。

Carbon dioxide is a nonhydrocarbon gas with high economic value and bright prospects in application. In the Huanghua Depression many high-content abiogenic CO_2 deposits were explored since 1960's. Through analysing the distribution characteristics of abiogenic CO_2 deposits and their relationship with Cenozoic tectonic activities, it is revealed that typical abiogenic CO_2 is distributed along the fault belt and fault intersection zones, and most of the deposits are distributed in the middle-northern Huanghua Depression. Areas with long term faulting, strong magmatism, and high geothermal gradients favor the generation and discharge of abiogenic gas. Deep faults, as pathways for mantle magma, may provide favorable pathways for the migration of mantle gas during extension. However, these NW-NWW trending faults, such as Haihe, Xuzhuangzi and Bogezhuang, are strike-slip faults in Cenozoic and the openness condition is bad. Only in the case when deep faults are intersected by NE or NEE trending extensional faults they could become favorable sites for discharge of abiogenic gases. For example, high-content abiogenic CO_2 deposits were explored in the intersections of the Xuzhuangzi and Gangxi faults. Further more, the intersections are also favorable locations for the ascent of deep heat flow. The heat of fault belts stems either from deep flow or dynamic metamorphism of carbonate rocks. Cenozoic magmatic activities not only released mantle origin CO_2, but also provided heat source for metamorphism of carbonate rocks. Cenozoic magmatic rocks in this area were originated from the partial melting of upper mantle. Faulting and regional spreading promoted the generation of magma and its intrusion into the crust. These magmatic rocks are distributed along NE-NEE trending faults. Magmatism ceased in the south of Huanghua Depression following the third stage of Shahejie Period, where only weak showings of abiogenic gas in the Cenozoic formation are known. However, in the middle-northern Huanghua Depression basalts occurred from the Shahejie Period to the Neogene and favored the discharge of abiogenic gases. The Cenozoic migration of the faulting and magmatism in Huanghua depression has close relationship with the distribution characteristics of abiogenic CO_2. Most of the aboigenic CO_2 is distributed in the middle-northern part. The faulting and magmatism in the middle-northern part of Huanghua Depression were most active between Shahejie and Dongying Period. The interval between the opening and closing of the faults is short, which is good for the reservation of CO_2.