Abstract: Triassic Xujiahe Formation,in Jiannan area of Sichuan Basin,was deposited in a braided river deltaic-lacustrine depositional system. The rock types of reservoirs are lithic sandstone,feldspathic-lithic sandstone and lithic-quartz sandstone,which were developed in braided river delta. The reservoirs in this area are characterized in low porosity and low permeability, with the average values of 5.96％ and 0.044×10^-3μm² respectively, which is mainly caused by sedimentary environment and diagenesis. The reservoirs of Xujiahe Formation were mainly formed in deltaic-braided channel depositional system,and the braided channel changed frequently in side-direction. Thus the sandstone and mud poorly sorted and poorly rounded grains, and low compositional maturity and low texture maturity of sandstone,which was not in favor of the development of primary pores. During early diagenesis process,compaction caused 60%～85% primary porosity loss, while the following cementation further decreased the porosity of 12％～18％ which made the sandstone denser. In addition,the Xujiahe Formation of research area was lack of soluble substances,the content of feldspar and carbonate cement were low,which weakened the dissolution in the later stage. The dissolution increased porosity with an average of 1％,and maximum of 2.5％.

Key words: Sichuan Basin, Jiannan area, Xujiahe Formation, low porosity-low permeability, formation mechanism

摘要： 四川盆地建南地区三叠系须家河组为辫状河三角洲—湖泊沉积体系,其储集层的岩石类型为辫状河三角洲沉积的岩屑砂岩、长石质岩屑砂岩、岩屑质石英砂岩。储集层平均孔隙度5.96％,平均渗透率0.044×10^-3μm²,具有明显的低孔低渗特征。须家河组储集层主要形成于三角洲辫状河道沉积,辫状河侧向改道频繁,砂泥混杂,颗粒分选及磨圆均较差,砂岩成分成熟度和结构成熟度均较低,不利于原生孔隙的发育;在早期成岩过程中,压实作用损失大量原生孔隙,压实作用损失的孔隙度一般占孔隙损失的60％～85％。随后的胶结作用使得砂岩更加致密,胶结物使孔隙减少12％～18％;此外,研究区须家河组缺乏易溶解的物质成分,长石和碳酸盐胶结物的含量较低,致使后期溶蚀作用微弱,因溶蚀作用增加的孔隙度平均为1％,最高达2.5％。

关键词: 四川盆地, 建南地区, 须家河组, 低孔低渗, 形成机理

CLC Number: 

• P588.22A