元坝深层礁滩气田基本特征与成藏主控因素

Basic characteristics of deep reef-bank reservoirs and major controlling factors of gas pools in the Yuanba Gas Field

四川盆地元坝气田主要气源岩为上二叠统龙潭组(吴家坪组),其生烃强度大,储层为上二叠统长兴组礁滩相白云岩,具有中低孔隙度、中低渗透率的特点,是一个受构造控制作用较小、以岩性圈闭为主,且埋藏深度大、高含硫化氢、常压、低地温梯度的大型气藏。东吴运动控制了晚二叠世沉积相与储层发育的位置,早中燕山运动控制了油气藏的形成,晚燕山运动以来的构造运动奠定了现今气藏的分布格局,适时发育的裂缝、大面积发育的礁滩相白云岩储层与烃源岩生烃高峰的有效匹配是气藏形成的关键。

The Upper Permian Longtan Fm(or Wujiaping Fm) is the major source rocks in the Yuanba Gas Field of the Sichuan Basin with strong hydrocarbon generation intensity.The dolomite reservoirs of reef-bank facies in the Upper Permian Changxing Fm have moderate-to-low permeability and porosity.More than that,gas reservoirs in this large-scale gas field are characterized by weak structural control,predominance of lihologic traps,large burial depths,high contents of H2S,normal pressures,and low geothermal gradients.The Dongwu movement controlled the Late Permian sedimentary faices and the location of reservoirs.The Early-Middle Yanshan movement controlled the formation of gas reservoirs.Tectonic movements since the Late Yanshan finalized the current distribution of gas reservoirs.The favorable timing of fracture development,development of the widely distributed dolomite reservoirs of reef-bank facies and peak hydrocarbon generation of source rocks is the key to gas accumulation.