四川盆地元坝地区茅口组高精度地震相分析

High-accuracy seismic facies analysis on Maokou Formation,Yuanba area,Sichuan Basin

为了精细描述四川盆地北部元坝地区中二叠统茅口组晚期沉积演化过程,明确茅口组晚期台地边缘高能浅滩展布和岩溶储层发育规律,以地震相为研究对象,通过实钻标定建立精细的地震等时格架,分析了研究区完钻井地震相与沉积相的对应关系,指出元坝地区茅口组高能浅滩叠合岩溶储层是油气勘探的有利方向,以高精度地震等时格架为约束的地震相分析方法是隐蔽性油气藏勘探发现的重要手段。研究结果表明:①元坝地区茅口组三段发育台地边缘高能滩沉积,呈北西向展布,前亚带为台地边缘丘滩带,地震剖面上呈丘状反射外形,厚度稳定,分布连续;后亚带为台地边缘浅滩带,地震剖面呈低频、断续、中强变振幅反射,为浅滩叠合岩溶缝洞带,两者均为油气勘探有利区。②等时格架内的波形分类是研究地层整体变化的有效手段,针对整个茅口组的波形分类结果准确地识别出了茅三段台缘展布和岩溶储层发育范围。③在明确相带的基础上,统计类属性能对元坝地区茅三段台缘浅滩叠合岩溶储层的横向变化进行精细刻画,较好地反映了储层物性的非均质性变化。

In order to precisely describe the sedimentary evolution in the Middle Permian Maokou period in Yuanba area,northern Sichuan Basin,and clarify the distribution of platform marginal high-energy shallow shoal and the development laws of karst reservoirs in this period,the seismic facies were taken as objectives to establish a fine seismic isochronal stratigraphic framework by means of drilling calibration.Then,the corresponding relationship between seismic facies and sedimentary facies was analyzed for drilled wells in the study area.Finally,it was pointed out that Maokou karst reservoirs superimposed with high-energy shallow shoal are the favorable oil and gas exploration targets,and the seismic facies analy⁃sis method constrained by high-accuracy seismic isochronal stratigraphic framework is the main means to explore and dis⁃cover subtle reservoirs.Results shows that(1)the deposits of platform marginal high-energy shallow shoal are developed in Maokou 3 Member in Yuanba area and distributed along northwest.Their frontal subzone is a platform marginal mound shoal zone,which is characterized by stable thickness and continuous distribution.And the reflection morphology in seis⁃mic profile is mound in shape.And their back subzone is a platform marginal shallow shoal zone,which presents the re⁃flection of low frequency,discontinuity,and moderate-strong variable amplitude.It is a karst fractured-vuggy zone superim⁃posed with shallow shoal.Both of them are favorable exploration targets;(2)waveform classification in the isochronal strati⁃graphic framework is an effective means to make clear the overall stratigraphic variation.And based on the classification results of the whole Maokou Formation,the distribution of marginal platform and the development scope of karst reservoirs of Maokou 3 Member are determined accurately;and(3)after determining facies belts,generic property statistics can de⁃scribe precisely the lateral variation of karst reservoirs superimposed with platform marginal shallow shoal in Maokou 3 Member,so as to reflect heterogeneous variation of physical properties better.