川西新场气田上三叠统须二、须四段相对优质储层成因差异性分析

Contributing Factor Divergence Analysis of Relative High Quality Reservoir of Upper Triassic in the 2nd and 4th Member of Xujiahe Formation of Xinchang Gas Field in West Sichuan

川西新场地区须家河组储层埋藏深度大、成岩作用复杂、致密化程度高,但在整体超致密背景下,局部仍发育较多的相对优质储层。相对优质储层在埋深较大的须二段,往往发育较多的原生孔隙,和相对次要的次生孔隙;而埋深较小的须四段储层,次生孔隙占绝对优势,原生孔隙发育较少。造成这一现象的主要原因是须二、须四段原生孔隙保存和次生孔隙发育机制上的差异。须二段储层中较多刚性颗粒的存在和较为发育的包膜绿泥石是原生孔隙得到较好保存的主要原因;而其较大的单砂层厚度和较少的泥岩发育则导致了有机酸性流体的注入量较少,长石溶蚀有限。须四段塑性岩屑含量明显较高,储层原生孔隙在压实作用下几乎消失殆尽,但较薄的单砂层厚度和较多泥岩的叠置发育使长石在有机酸性流体作用下得到了充分溶蚀;这是须四段储层次生孔隙相对发育、长石含量很低、同时还有自生高岭石沉淀的主要原因。

Major relative high quality reservoirs are locally developed in the context of the entire super densified Xujiahe Formation in Xinchang in west Sichuan.They have a great burial depth,complicate diagenesis,and high density.The relative high quality reservoir is in the 2nd member of Xujiahe Formation with a big burial depth,which developed more primary pores than secondary pores;while the 4th member of Xujiahe Formation with small burial depth developed more secondary pores than primary pores.The main reason of this appearance is the divergent mechanisms of the primary pore conservation and secondary pore development of the 2nd and 4th member of Xujiahe Formation.Theexistence of the relatively developed encapsulating chlorite and the harsh particulates led to the well conservation of the primary pores in the 2nd member of Xujiahe Formation;while the single thick sand and the undeveloped mudstone layer cause the poor influx of organic acid fluid,so that the feldspar corrosion is limited.As for the 4th member of Xujiahe Formation,the plasticity of the rocks is relatively high;this,in turn,resulted in the disappearance of the primary pores under the diagenetic compaction,while the secondary pores are relatively popular with minor authigenic kaolinite sedimentated,multiple thin single sand and mudstone developed,and sufficient feldspar corroded by organic acid fluid.