湖相致密储层有利层段的沉积与湖平面变化的耦合关系及其控制因素：以柴西尕斯地区上干柴沟组下段为例

Coupling relationship between sedimentation of favorable intervals and lake level change and its controlling factors in lacustrine tight reservoir: A case study of the Lower Shangganchaigou Formation in the Gasi area, western Qaidam Basin, China

关键词:  柴达木盆地  湖相致密储层  湖平面变化  有利层段  Fischer图解  自然伽马

Key words:  Qaidam basin  lacustrine tight reservoir  lake level change  favorable interval  Fischer plots  natural gamma-ray

摘要:

探讨有利层段的沉积与湖平面变化之间的关系，可以对湖相致密储层的勘探开发部署提供一定参考。以柴达木盆地西部尕斯地区上干柴沟组下段为例，利用自然伽马（GR）曲线资料，进行Fischer图解和铀含量（U）－有机碳（TOC）回归拟合法，重建渐新世沉积时期湖平面变化过程，结合磁化率资料，讨论了湖平面变化的气候控制作用。结果表明：（1）尕斯地区上干柴沟组下段泥质含量和TOC含量变化趋势一致，均反映其在沉积过程中经历了两次湖退和湖进过程，有利于烃源岩和储层的形成；（2）湖平面上升期形成的高水位沉积体系，对应于致密砂岩类储层中优质烃源岩的富集层段，能有效形成源－储共生配置；（3）渐新世湖平面变化受西风条件下的气候的控制，西风带来的水汽，形成相对湿润的气候条件，引起湖平面的上升，有利于烃源岩的形成，且与有利层段的沉积呈现耦合关系。

Abstract:

Exploring the relationship between favorable sedimentary intervals and the change of lake level can provide some reference for the exploration and development deployment of the lake-phase dense reservoir. In this study, taking the Oligocene Lower Shangganchaigou Formation in the Gasi area of the western Qaidam Basin as an example, Fischer diagrams and U-TOC regression fitting method were used to reconstruct the process of lake level change during the Oligocene sedimentary period using Natural gamma ray (GR) curve data, and the climate controlling factors of lake level change were discussed in combination with magnetic susceptibility data. The results show that: (1) The Fischer diagram of Lower Shangganchaigou Formation in the Gasi area is consistent with the trends of mud content and TOC content, all reflecting that it has undergone two lake retreat and lake advance processes during deposition, which are favorable for the formation of source rocks and reservoirs; (2) The high water level sedimentary system formed during the lacustrine rising period corresponds to the enrichment intervals of high-quality source rocks in tight sandstone reservoirs, which can effectively form a source-reservoir symbiotic configuration; (3) The change of lake level in the Oligocene was controlled by the climate under the westerly wind condition. The water vapor brought by the westerly wind formed relatively humid climate conditions and caused the rise of lake level, which was favorable for the formation of source rocks and presented a coupling relationship with the deposition of favorable intervals.