柴北缘冷湖地区古近系路乐河组成岩作用及有利成岩相研究

Diagenesis and Favorable Diagenetic Facies of Paleogene Lulehe Formation Sandstone in Lenghu Region

通过钻井岩心、铸体薄片、扫描电镜及测录井资料,对柴达木盆地北缘冷湖地区古近系路乐河组的成岩作用特征、成岩相类型及其有利成岩相进行了系统研究。结果表明:研究区储层成分成熟度和结构成熟度均较低,成岩作用类型复杂多样,主要发育压实作用、胶结作用、交代作用和溶蚀作用,成岩演化主体进入中成岩阶段B期。综合考虑各种成岩现象及特征、孔隙类型及沉积微相特征,将研究区储层成岩相划分为强压实致密成岩相、碳酸盐胶结成岩相、绿泥石薄膜胶结-粒间孔成岩相、不稳定组分溶蚀-次生孔成岩相4类。优质储集层的分布与成岩相类型关系密切,压实致密成岩相和碳酸盐胶结成岩相的储层物性普遍较差,多为致密储层,集中分布于扇三角洲平原河道翼、扇三角洲水下分流河道边部,而主要发育于扇三角洲前缘水下分流河道、河口坝中上部较厚砂体中的绿泥石薄膜胶结-粒间孔成岩相和不稳定组分溶蚀-次生孔成岩相的原生孔隙或次生孔隙发育,储层物性较好,利于油气富集,为研究区储层的有利成岩相。

Using drilling core observation, casting thin sections identification, scanning electron microscopy （SEM） and combining with logging and mud logging data, this study carries out a systematically research on the characteristics of diagenesis, type of diagenetic facies and favorable diagenetic facies of Paleogene Lulehe Formation sandstone in Lenghu region of the northern Qaidam Basin. The results show that reser- voir compositional maturity and textural maturity are low, and the reservoir has experienced complicated diagenesis, mainly including compaction, cementation, replacement and dissolution. The reservoir in the study area is mainly at the middle diagentic stage B period. This paper classifies 4 diagenetic facies belts, including dense strong compaction diagenetic facies, carbonate cement diagenetic facies, chlorite coat ce- mentation-intergranular pore diagenetic facies~ and unstable comoponents dissolution secondary pore diage- netic facies by comparing all kinds of diagenetic phenomena and features, pore types and sedimentary mi- crofacies. The distribution of high quality reservoir has a close relationship with diagenetic facies. The res- ervoir property of dense strong compaction diagenetic facies and carbonate cement diagenetic facies are gen- erally poor, mostly which are tight sandstones with low permeability mainly distributing in flank of fan delta plain river and the edge of fan delta distributary channel. However, chlorite coat cementation interg- ranular pore diagenetie facies and unstable comoponents dissolution secondary pore diagenetic facies mainly developing in the thick subaqueous distributary channel, the middle and the upper part in the mouth bar sand body of the fan delta front are enrichment for oil and gas reservoirs and are the favorable diagenetic facies in the study area due to the better reservoir property from primary pore and secondary pore develop- ment.