塔里木盆地古城地区奥陶系滩相白云岩气藏特征及主控因素

Characteristics and main control factors of Ordovician shoal dolomite gas reservoir in Gucheng area,Tarim Basin,NW China

以地震、钻井和实验分析为基础,对塔里木盆地古城地区奥陶系鹰山组三段滩相白云岩气藏特征及成藏主控因素进行研究。结果表明,古城地区白云岩气藏类型为“滩-断双控”的岩性气藏,其形成主要受以下因素控制:①持续发育的古构造背景是天然气聚集的有利指向区;②台缘缓坡环境沉积的大面积中—高能颗粒滩是白云岩储集层形成的物质基础;③大气淡水淋滤、白云石化作用叠加断裂带流体溶蚀改造是优质白云岩储集层形成的关键因素;④天然气来源于古油藏裂解和烃源岩分散有机质生烃,北北东向走滑断裂是天然气垂向运移的优势通道;⑤鹰山组一、二段灰岩盖层为气藏形成提供了直接遮挡条件。在此基础上综合分析,指出古城地区鹰山组三段近南北向发育的3个颗粒滩带和北北东向展布的7条走滑断裂带共同控制了滩相白云岩气藏的发育。

Based on seismic,drilling data and experimental analysis,the characteristics and main controlling factors of shoal dolomite gas reservoir in the third member of Ordovician Yingshan Formation of Gucheng area,Tarim basin were examined.The study shows that the dolomite gas reservoir in Gucheng area is lithologic gas reservoir controlled by shoal and fault jointly,and its formation is mainly attributed to the following factors:(1)The continuously developing paleotectonic structure has been in the direction of gas migration and accumulation;(2)The large area of medium-high energy grain bank deposited in gentle slope environment is the material basis for the formation of dolomite reservoir;(3)Atmospheric water leaching and dolomitization and fluid dissolution in fault zone are the key factors for the formation of high-quality dolomite reservoir;(4)The natural gas comes from cracking of the ancient oil reservoir and hydrocarbon generation of dispersed organic matter in source rocks,and the NNE-trending strike-slip fault is the dominant channel for vertical migration of natural gas;(5)Limestone cap rocks in the first and second members of Yingshan Formation provide direct sealing for the formation of gas reservoir there.On the basis of comprehensive analysis,it is pointed out that the Gucheng area has three grain shoal zones in the third member of Yingshan Formation in nearly S-N direction,which together with seven strike-slip fault zones in NNE direction control the development of shoal dolomite gas reservoir.