川西坳陷中段西部雷四段气藏沉积层序及其对储层的控制

Sedimentary and sequence characteristics of Leikoupo formation's gas pool 4 in the western Sichuan basin and their control on reservoir development

为确定川西坳陷中段西部气藏的有利储层发育层段,利用薄片、岩心、测井、地震等资料,研究雷口坡组四段(简称雷四段)沉积层序,分析它对储层发育的控制。结果表明,雷四段可划分为一个完整的三级层序和三个四级层序,其中雷四上亚段对应上部四级层序,进一步划分为四个五级和多个六级高频层序,由向上变浅的高频沉积旋回组成;井间高频层序类型相似,横向一致性对比好,表明形成环境近似。雷四上亚段主要发育潮坪相的潮间带和潮下带亚相沉积,纵向上岩性变化频繁,横向上分布较为稳定;潮间带是储层发育的有利亚相,以Ⅱ、Ⅲ类储层为主,发育于上、下两个储层段中上部,对应五级和六级高频层序的中上部;高频层序反映的相对海平面变化控制潮间带有利岩相分布,影响后期成岩作用,是储层发育与空间展布的关键。

In order to determine the favorable reservoir development of gas reservoirs in the western part of the middle area west Sichuan depression,based on detailed observation of cores,thin section from well cores samples under microscope observation,combined with logging curves characteristics analysis and seismic data,sedimentary sequence characteristics from middle Triassic Leikoupo formation 4(Lei member 4)are investigated in the western part of the middle area west Sichuan depression.The control factors of reservoir development controlled by sedimentary sequence are analyzed.The research results show that Leikoupo formation can be divided into one third-order sequences and three fourth-order sequences,and Leikoupo formation 4upper sub-member are located at the uppermost fourth-order sequences and may be further divided into four fifth-order sequences and multiple sixth-order sequences.High frequency sequence has the characteristics of sedimentary assemblages obviously tapering upward.The high frequency sequence type is similar to the well and their horizontal comparison is good,which shows they were deposited in the similarity of sedimentary environment.The sedimentary environment mainly belongs to tidal flat deposits in the western part of the middle area west Sichuan depression and the tidal flat deposits mainly develop intertidal zone and subtidal zone sub-facies.The lithology of flat deposits varies in the vertical lithology and is more stable in horizontal orientation.The intertidal zone is advantageous sub-facies of reservoir development.Reservoirs generally are dominated by classⅡand classⅢreservoir.The favorable location of reservoirs development is mainly distributed in middle-upperpart of the upper reservoir and the lower reservoir,corresponding to the location in the middle and upper part of the five-order and six-orderl high frequency sequence,respectively.The favorable intertidal lithofacies distribution of reservoir development is controlled by high frequency sequence reflecting sea level change,which also has a certain impact to late diagenesis.The high frequency sequence is the key factor to affect reservoir development and spatial distribution.