四川盆地威远—高石梯地区二叠系栖霞阶层序地层特征及有利储层分布

Sequence stratigraphic characteristics and favorable reservoirs distribution of Permian Qixia Stage in Weiyuan-Gaoshiti area,Sichuan Basin

通过岩心、岩屑和测录井资料,对四川盆地威远—高石梯地区二叠系栖霞阶层序地层特征进行了综合分析,指明了有利储层分布及控制因素。研究结果表明:(1)威远—高石梯地区二叠系栖霞阶可识别出2个Ⅰ型层序界面(梁山组底界面和栖霞组顶界面)和2个Ⅱ型层序界面(栖一段顶界面和栖二b段顶界面),据此将栖霞阶划分为层序SQ1,SQ2和SQ3,分别对应梁山组+栖一段、栖二b段、栖二a段。(2)研究区栖霞阶层序格架和平面分布特征显示,底部地层(SQ1)具有向沉积前古地貌高地超覆的特征,中上部地层(SQ2和SQ3)由沉积期地貌高地不断向低处迁移,呈现出“底超、中上部迁移”的层序充填规律。(3)研究区SQ2和SQ3高位体系域沉积时期,古地貌高地和坡折带发育厚度大、横向连续性较好的丘滩复合体,奠定了储层发育的物质基础,该时期海平面频繁升降,丘滩复合体发生高频暴露岩溶作用,使得储集性能得到改善,叠加白云岩化作用后形成抗压溶骨架,有利储层发育。(4)沉积相和岩溶作用控制了白云岩薄储层的发育和分布,栖霞阶沉积期高地和坡折带为下一步勘探的潜力区。

Based on cores,cuttings and logging data,the sequence stratigraphic characteristics of Permian Qixia Stage in Weiyuan-Gaoshiti area of Sichuan Basin were comprehensively analyzed,and favorable reservoir distribution and controlling factors were pointed out.The results show that:(1)Two typeⅠsequence boundaries(bottom boundary of Liangshan Formation and top boundary of Qixia Formation)and two typeⅡsequence boundaries(top boundary of Qi 1 member and top boundary of Qi 2b member)were identified in Permian Qixia Stage in Weiyuan-Gaoshiti area.Accordingly,the Qixia Stage was divided into SQ1,SQ2 and SQ3,corresponding to Liangshan Formation and Qi 1 member,Qi 2b member and Qi 2a member,respectively.(2)The sequence filling framework and sequence plane distribution characteristics of Qixia Stage show that the bottom stratum(SQ1)has the characteristics of onlapping to the pre-depositional palaeogeomorphology highland,and the middle and upper strata(SQ2 and SQ3)continuously migrate from the sedimentary geomorphic highland to the lowland,showing the sequence filling pattern of onlapping at the bottom and migration at the middle-upper.(3)During the sedimentary period of SQ2 and SQ3 highstand systems tracts in the study area,mound-shoal complexes with large thickness and good lateral continuity were developed in the paleogeomorphology highlands and slope breaks,which laid material foundation for reservoir development.During that period,the sea level was in high-frequency change.The mound-shoal complexes high-frequency exposure karstification,improving the reservoir properties,and the pressure-soluble skeleton formed after the early dolomitization,which is beneficial to the development of the reservoir.(4)The development and distribution of thin dolomite reservoirs are controlled by sedimentary facies and karstification.The highlands and slope breaks in Qixia Stage are potential areas for next exploration.