豫西地区中、下二叠统沉积特征

DEPOSITIONAL FEATURES OF MID—LOWER PERMIAN IN WEST HENAN AREA

豫西地区中、下二叠统太原组、山西组、上石盒子组及下石盒子组煤成气资源丰富 ,但成煤环境纵向发育与横向变化较大 ,规律难于把握。因此 ,开展煤成气源岩沉积环境研究有利于该区煤成气资源的勘探与开发及合理的利用。通过露头、钻井、地震资料及分析、测试资料的综合研究认为 :本区中、下二叠统主要沉积了一套浅海碳酸盐岩 ,海湾—泻湖、潮坪、沼泽、障壁岛 (砂质滩、坝 )及三角洲相陆源碎屑岩和煤层。从总的沉积特征来看 ,下二叠统太原组、山西组基本上发育滨、浅海相碳酸盐岩、陆源碎屑岩和煤的混合沉积。上二叠统上、下石盒子组则以海陆交互相陆源碎屑沉积为主 ,三角洲及三角洲平原沼泽十分发育 ;沉积环境具有自下而上 ,自南东向北西方向由海相逐步过渡为陆相的基本特点。其煤成气源岩沉积环境以早二叠世山西期潮坪、泻湖过渡带之滨岸沼泽环境为最佳 ,其次为中二叠世下石盒子期三角洲平原沉积之平原沼泽环境。

There are abundant coal formed gas in the formations of Taiyuan,Shanxi,Upper and Lower Shihezi of Mid—Lower Permian in West Henan area.But it is difficult to predict the distribution pattern in exploration practice because the coal forming environments vary both vertically and laterally.Therefor,it is necessary to study the depositional environments of the coal formed gas source rock for the benefit of exploration and development.Through investigating the data of crop,seismic,drilling,core and logging,it is concluded that a set of shallow marine carbonate,terrigenous clastics and coal beds consisting of gulf—lagoon,tidal platform,swamp,bars and delta facies is mainly deposited in the area.In the light of overall features,A combined deposition of coastal and shallow marine carbonate,terrigenous clastics and coalbeds is developed in Taiyuan and Shanxi formations of Lower Permian;while terrigenous clastics with marine—continental facies are dominantly in Shihezi formation of Upper Permian,delta and deltaic plain swamp are very developed.The depositional environments have the basic characteristics of progressing upward and north westward from marine facies to continental facies.The best depositional environment of coal formed gas source rock is the coastal swamp on the transition zone between the tidal platform and the lagoon in Shanxi period,and the second is the plain swamp of the deltaic plain in Lower Shihezi period of Middle Permian.