四川盆地雷口坡组台内滩与台缘滩沉积特征差异及对储层的控制

Difference in depositional characteristics between intra-platform and marginal-platform shoals in Leikoupo Formation,Sichuan Basin and its impact on reservoirs

四川盆地在中三叠统雷口坡组沉积时期处于局限—蒸发台地—台地边缘沉积环境,勘探实践证明雷口坡组的储层发育台内滩和台缘滩两类颗粒滩,不同类型的颗粒滩储层具有明显分异。通过对两类颗粒滩特征及形成条件的深入分析,指出台缘环境浪基面影响深度最大可达20m,沉积物可容空间大,形成的单滩体厚度大,早期暴露几率小,较大的上覆地层静压易使颗粒呈格架支撑,喉道减小,有利于滩体内部粒间孔保存,储集空间以(溶扩)残余粒间孔为主;而由于台缘环境的遮挡,台内环境的浪基面影响深度一般为2～3m,颗粒滩在局部微地貌高地发育,厚度较小,暴露几率大,早期大气淡水可影响单旋回台内滩中上部,储集空间以粒内溶孔和铸模孔为主。沉积环境形成的物质基础是后期成岩演化与孔隙演化的关键,影响了颗粒滩储层最终的储集面貌。

The Leikoupo Formation in Sichuan Basin was deposited in a restricted evaporative platform or margin platform environment.Exploration practice has indicated that in the Leikoupo reservoir developed two kinds of grain shoals,i.e.intra-platform shoal and marginal-platform shoal,which are distinctly different.With thorough analyses on characteristics and formation conditions of these two shoals,the present paper showed that the marginal-platform shoal had a wave base up to 20 m in maximum and a large available space for sediments,forming shoals with big thickness for an individual one and less exposure.Greater static pressure of overlying formations resulted readily in a trellis support for grains and the decreased throat port,favoring the preservation of intergranular space within shoals and the formation of reservoir space dominated by residual intergranular pores（dissolved enlargement）.While the intra-platform shoal had a wave base ranging generally between 2～3 m due to a shelter of the marginal-platform environment and grain shoals developed in local micro-topographic highland with minor thickness and frequent exposure.Fresh water in the early atmosphere might influence the middle and upper parts of a mono-cyclic intra-platform shoal,resulting in the reservoir space dominated by intragranular karst and moldic pores.A material basis laid by environments is a key to diagenetic and porous evolutions at the late stage,exerting an effect on the final reservoir features of grain shoals.