依南地区下侏罗统砂岩储层致密化因素分析

Densification Origin of Lower Jurassic Tight Sandstone Reservoir in Yi'nan Area

为了明确库车坳陷依南地区下侏罗统致密砂岩储层致密化的控制因素,基于岩心观察、普通薄片和铸体薄片描述对比,剖析研究区东部、中部和西部下侏罗统致密砂岩储层的基本特征差异。在此基础上,通过相关性分析,从沉积条件、岩石学特征及成岩作用等几方面探讨储层致密化的控制因素。结果表明:相比研究区中部和西部地区,东部地区的储层埋藏深度更浅、压实程度较弱、泥质含量较低、长石岩屑砂岩含量更高、高岭石含量较高、伊利石含量相对较低、溶蚀孔隙含量较高、储层非均质性较弱,储层物性总体较好。沉积因素是研究区下侏罗统砂岩储层致密化的先决条件,沉积环境中泥质含量和地层埋藏深度与储层物性呈明显的负相关关系;岩石学特征是导致储层致密化的根本原因,长石含量和岩石粒度大小与储层物性具有正相关关系,黏土矿物(伊利石)、胶结物含量与储层物性呈负相关关系;成岩作用是储层致密化的关键因素,压实作用、黏土矿物、硅质和碳酸盐矿物的胶结作用以及黏土矿物和碳酸盐矿物的交代作用是导致储层物性变差的主要原因,而长石溶蚀作用在一定程度上改善了储层物性。

In order to clarify the controlling factors of reservoir densification of the lower Jurassic tight sandstone in Yi'nan area of Kuqa depression,the difference of the basic characteristics of the lower Jurassic tight sandstone reservoirs in the eastern,central and western of the study area are analyzed comparatively by core observation,common and cast thin section description.On this basis,the controlling factors of reservoir densification are discussed from the aspects of sedimentary conditions,petrological characteristics and diagenesis through correlation analysis.The results show that,compared with the central and western regions,the reservoir in the eastern region of the study area has shallower buried depth,weaker compaction degree,lower shale content,higher content of feldspar fragment sandstone and kaolinite,lower illite content,more dissolved pores,weaker reservoir heterogeneity,and it has better physical property.Sedimentary factors are the prerequisite for the densification of the lower Jurassic sandstone reservoir in the study area.The shale content and buried depth of reservoir in the sedimentary environment are negatively correlated with the reservoir physical properties.Petrological characteristics are the fundamental cause of reservoir densification.The content of feldspar and grain size of rock are positively correlated with reservoir physical properties,while the content of clay mineral(illite)and cement are negatively correlated with reservoir physical properties.Diagenesis is the key factor of reservoir densification.Compaction,cementation of clay minerals,siliceous and carbonate minerals and metasomatism of clay minerals and carbonate minerals are the main reasons for the deterioration of reservoir physical properties,while feldspar dissolution improves the reservoir physical properties to a certain extent.