四川盆地马路背地区上三叠统须家河组致密砂岩储层成因分析

Origin Analysis of a Tight Sandstone Reservoir for the Xujiahe Formation of the Upper Triassic at the Malubei Area in the Sichuan Basin,China

马路背构造位于四川盆地东北部,该地区须家河组发育致密砂岩储层,却形成了“高产、稳产”的规模气藏。论文充分利用各种岩矿分析化验资料,从岩石学特征、成岩作用、孔隙演化等方面深入探讨了马路背地区须二段(T_(3)x^(2))致密砂岩储层的成因。结果表明:马路背地区须家河组以大巴山变质岩为母岩沉积了一套三角洲前缘中粒岩屑砂岩和石英砂岩;无论是石英砂岩还是岩屑砂岩,无论埋深大小,铸体薄片下孔隙均不发育,扫描电镜偶见微孔,物性很差;强烈的埋藏压实作用造成各种孔隙的缩小与消失;早燕山期(199~100 Ma)、中晚燕山期(100~65 Ma)、喜山期(65 Ma以来)等多期构造强挤压进一步造成孔隙减小和消失,构造压实减孔量大约4%;埋藏压实与构造强压实减孔的同时,产生了不同规模断层和裂缝(颗粒裂纹—粒间微裂缝—层间断层),沟通微孔,形成断层—裂缝—微孔隙组成的断缝储集体。这类储集体主要受构造应力大小控制,构造挤压最强的部位,裂缝最发育;其次受岩性和砂岩厚度控制,中—薄层石英砂岩中最发育。

A large-scale gas reservoir of high and stable production has been found in the upper Triassic Xujiahe Formation in the Malubei area,northeastern Sichuan Basin.Based on all kinds of test data,this paper discusses the origin of the tight sandstone reservoir in the second member of the Xujiahe Formation(T_(3)x^(2)),according to its petrological characteristics,diagenesis,and pore evolution.The results show that:(1)Lithic sandstone and quartz sandstone of delta front,whose parent rocks were derived from the metamorphic rocks of the Daba Shan,were deposited in the Xujiahe Formation at the Malubei area;(2)We cannot identify many pores from the casting slice and cores,and only a few micropores can be seen using a scanning electron microscope.This tight reservoir has poor physical properties,no matter whether it is quartz sandstone or lithic sandstone,at any burial depth or any grain size;(3)Strong burial compaction results in the reduction and disappearance of various pores;(4)The strong compressions during the early Yanshan tectonic(199-100 Ma),middle to late Yanshan tectonic(100-65 Ma),and Himalayan tectonic(since 65 Ma)stages further reduced the porosity about 4%;and(5)While the burial compaction and strong tectonic compaction reduced the pores,different scale faults and fractures(particle crack,intergranular micro fracture,and layer discontinuity)were also produced,connecting micropores and forming fault fracture reservoirs composed of faults,fractures,and micropores.This kind of reservoir is mainly controlled by the tectonic stress,while the position with the strongest tectonic compression has developed the most fractures.Secondly,it is controlled by the lithology and sandstone thickness,while most good reservoirs developed in middle to thin layer of the quartz sandstone.